Part 2
The cold chain from carcass
to consumer
6
Primary chilling of red meat
6.1 Introduction
The increased application of temperature legislation in many countries,
coupled with economic requirements to maximise throughput, minimise
weight loss and operate refrigeration systems in the most efficient manner,
has created a very large demand for process design data on all aspects of
carcass chilling. Concurrently there has been a growing realisation of the
importance of chilling rate on meat saleability, in terms of drip potential
(see Chapter 2), appearance (see Chapter 4), and eating quality, particu-
larly texture (see Chapter 3).
EU temperature legislation governs the chilling of beef, pork and lamb
for the majority of abattoirs within the community. The only derogations
are for very small abattoirs and for retail shops cutting meat for direct
sale to the final consumer. The EC legislation does not define a chilling
time, only a maximum final meat temperature of 7 °C before transport or
cutting.
Abattoir management and refrigeration contractors require reliable
design data, relating processing variables to chilling time and weight loss,
so that they can specify and design carcass cooling systems to meet differ-
ing requirements.To optimise fully such systems, knowledge is also required
of the product heat load, and its variation with time, so that the refrigera-
tion machinery can be sized to achieve the required throughput.
It is also important that the industry is made aware of a growing number
of alternatives to conventional batch air chilling systems. Many of the alter-
native systems offer significant advantages in terms of increased through-
put, lower costs and increased product quality.
6.2 Conventional chilling
The majority of carcass meat is chilled in conventional chill rooms nomi-
nally operating at one or sometimes two conditions during the chilling cycle.
Most of the factors that control the chilling process are common to all
species and are covered in the following section on beef. Specific consid-
erations for sheepmeat, pork and offal are outlined in their respective
sections.
6.2.1 Beef
This section brings together design data on many aspects of the chilling of
beef sides. Effects of environmental, carcass and operational variables on
the rate of chilling and evaporative weight loss in single stage air chilling
systems are described in detail. Data are also presented on the rate of heat
release from sides that are encountered in these cooling operations. Using
conventional single stage chilling regimes it is evident that only relatively
light (<105 kg), lean beef sides can be cooled to 7 °C in the deep leg during
a 24 h operating cycle, whilst evaporative losses are of the order of 2%.
Despite the general absence of specific regulations for chilling time, the
time required to cool a side to a specified maximum temperature is the most
important commercial factor determining the cost and operation of a
cooling system. If sides cannot be chilled within 18h, which is the time avail-
able in one day, making allowance for loading, unloading and cleaning, they
will probably remain in chill for a further 24h. Chilling facilities will then
have to be twice as large, with considerably increased capital investment
and running costs. Some investigations on the continuous chilling of beef
(Drumm et al., 1992a,b) have been carried out but such systems are not
widely used.
Increasing attention is now being paid to the reduction in energy con-
sumption, but it has been shown that in commercial chilling operations the
cost of evaporative weight loss in beef sides (Collett and Gigiel, 1986) are
at least an order of magnitude higher than the energy costs.
Major investigations to provide such data have been carried out at
Food Refrigeration and Process Engineering Research Centre (FRPERC),
Langford (formerly the Meat Research Institute) (Bailey and Cox, 1976;
Cox and Bailey, 1978) and at the National Mechanical Engineering
Research Institute, Pretoria (Kerens and Visser, 1978; Kerens, 1981). Pub-
lished information from these investigations and others has been brought
together in this section together with some unpublished material.
6.2.1.1 Effect of environmental and carcass variables on cooling rate
Air temperature, air velocity, and to a limited extent, relative humidity, are
the environmental factors that affect the cooling time of beef sides. Cooling
rate will also be a function of the weight and fat cover of a given side.
100 Meat refrigeration
6.2.1.1.1 Air temperature
The results of the programme on beef chilling carried out at Langford
clearly show the importance of air temperature on cooling time (Bailey and
Cox, 1976). For ease of use the results of the investigations have been pre-
sented as four plots of the logarithm of temperature against time covering
a wide range of side weights (100–220 kg) and air velocities (0.5–3.0 ms
-1
).
Data for the slowest cooling area of the side, which was located by insert-
ing a probe into the centre of the thickest section of the leg, are shown in
Fig. 6.1 and can therefore be used to determine the environmental condi-
tions required to attain a desired cooling time when a maximum final tem-
perature has been specified. Potential surface freezing problems can then
be evaluated from the surface temperature plots (Figs. 6.2 and 6.3). These
in conjunction with the deep M. longissimus dorsi data (Fig. 6.4) also
identify toughening problems and the possible requirement for electrical
stimulation.
Cooling in air at a constant 4°C, compared with 0 °C, at 3m s
-1
will
increase the time to reach 7 °C in the deep leg of a 100kg side from 20.3 to
27.7 h (a 36% increase). At 0.5 ms
-1
, the time for a 220 kg side to reach 7 °C
will increase from 45.9 to 68.3 h (a 49% increase). In systems designed to
produce fully chilled sides, with average meat temperatures of 2–4 °C, the
requirement for low air temperatures becomes even more important
because of the small meat/air temperature difference at the end of the
process.
Primary chilling of red meat 101
38·538·538·5
353535
30
30
30
25
25
25
20
20
20
15
15
15
10
10
7
5
4
3
7
10
2
1
5
9
0 2 46 8 10 12 14 16 18 20 22 24 26 28 30 32 34
0·01
0·02
0·03
0·04
0·05
0·06
0·07
0·08
0·09
0·1
0·2
0·3
0·4
0·5
0·6
0·7
0·8
0·9
1·0
0·5
0·5
0·5
Y
1
1
23
2
1
0·5
3
2
1
3
23Air speed (m s
–1
)
Time post-mortem (h)
Deep long. dorsi temperature (
°
C)
Chiller
air
temperature
(°C)
840
Side weights
100
140
180
220
Approximate average for British abattoirs
kg
Fig. 6.1 Relationship between deep longissimus dorsi temperature and cooling
time for beef sides (source: Bailey and Cox, 1976).
38·5
35
30
25
20
15
10
7
5
4
3
2
1
38·5
35
30
25
20
15
10
7
5
38·5
35
30
25
20
15
10
9
0 8 16 24 32 40 48 56 64 72 80 88 96 104
0·01
0·02
0·03
0·04
0·05
0·06
0·07
0·08
0·09
0·1
0·2
0·3
0·4
0·5
0·6
0·7
0·8
0·9
1·0
0·5
0·5
0·5
Y
1
1
23
2
10·5
3
2
1
3
23
Air speed (m s
–1
)
Time post-mortem (h)
Deep leg temperature (
°
C)
Chiller
air
temperature
(°C)
840
Side weights kg
100
140
180
220
Approximate average for British abattoirs
Fig. 6.2 Relationship between deep leg temperature and cooling time for beef
sides (source: Bailey and Cox, 1976).
38·538·538·5
3535
30
30
25
25
20
20
15
15
10
7
10
35
30
25
20
15
10
7
5
4
3
2
1
5
9
0 2 468 10 12 14 16 18 20 22 24 26 28 30
0·01
0·02
0·03
0·04
0·05
0·06
0·07
0·08
0·09
0·1
0·2
0·3
0·4
0·5
0·6
0·7
0·8
0·9
1·0
0·5
0·5
0·5
Y
1
1
2
2
1
0·5
3
2
1
3
3
2
3
Air speed (m s
–1
)
Time post-mortem (h)
Surface long. dorsi temperature (
°
C)
Chiller
air
temperature
(°C)
840
Side weights kg
100
140
180
220
Approximate average for British abattoirs
Fig. 6.3 Relationship between surface longissimus dorsi temperature and cooling
time for beef sides (source: Bailey and Cox, 1976).
Provided air temperatures are chosen to avoid substantial surface freez-
ing it is quite feasible to determine the cooling time for any other air tem-
perature using Figs. 6.1 to 6.4. The fractional unaccomplished temperature
on the Y axis can be replaced by the meat temperature calculated by:
[6.1]
where t is the meat temperature, t
i
is the initial meat temperature and t
f
is
the air temperature.
The experimental data used to produce the figures were obtained in
powerful refrigeration systems where the initial temperature pull down
period was minimal. Commercial systems with long pull down periods take
considerably longer to cool because initial air temperatures are higher
than the required design figure.
6.2.1.1.2 Air velocity
Increasing the air velocity during chilling produces a substantial reduction
in chilling times at low air velocity but similar increases at higher velocities
have a much smaller effect (Table 6.1).
Ytttt=-()-()
fif
Primary chilling of red meat 103
38·538·538·5
3535 35
30
30
25
25
20
20
15
15
10
7
10
30
25
20
15
10
7
5
4
3
2
1
5
9
0816 24 32 40 48 56 64 72 80
0·01
0·02
0·03
0·04
0·05
0·06
0·07
0·08
0·09
0·1
0·2
0·3
0·4
0·5
0·6
0·7
0·8
0·9
1·0
0·5
0·5
0·5
Y
1
1
2
2
1
0·5
3
2
1
3
3
2
3Air speed (m s
–1
)
Time post-mortem (h)
Surface leg temperature (
°
C)
Chiller
air
temperature
(°C)
8 4 0
Side weights kg
100
140
180
220
Approximate average for British abattoirs
Fig. 6.4 Relationship between surface leg temperature and cooling time for beef
sides (source: Bailey and Cox, 1976).
The power required by the fans to move the air increases with the cube
of the velocity. A four-fold increase in air velocity from 0.5 to 2ms
-1
results
in a 4–7 h reduction in chilling time for a 140 kg side weight, but requires a
64-fold increase in fan power. Further increasing air velocity to 3 m s
-1
only achieves an extra 6–8% reduction in chilling time. In most practical
situations it is doubtful whether an air velocity greater than 1 m s
-1
can be
justified.
6.2.1.1.3 Relative humidity
A small number of investigations (Kerens and Visser, 1978) have shown
that decreased relative humidity (RH) results in slight reduction in chilling
time, apparently caused by increased evaporative cooling from the carcass
surface. However, unless water is added to the surface of the carcass, any
increase in the rate of evaporation will be directly reflected in a larger
weight loss. It is therefore difficult to envisage a commercial situation where
the installation of small, high temperature difference (TD) evaporators with
attendant lower relative humidities would be economically viable.
6.2.1.1.4 Side weight
The marked effect of side weight on chilling time (Table 6.2) is a clear
problem in chill room design and operation. In most practical situations it
is impossible to load chilling systems with batches of matched weight sides
or to remove sides in a weight-based order. A compromise must therefore
be made between overcooling the light-weight sides and undercooling
heavy sides. Overcooling can lead to excessive weight loss while under-
cooling can shorten shelf-life and overload the refrigeration systems of
transport vehicles. Subsequent slow cooling in transport vehicles results in
a further reduction in shelf-life.
6.2.1.1.5 Fat cover
It is difficult to separate the effect of fat cover from that of carcass weight.
Experimental investigations are hampered because light animals tend to be
104 Meat refrigeration
Table 6.1. Chilling time (in h) to a deep bone temperature of 10 °C in beef sides
of 105 and 140 kg in air at 0 °C, 95% relative humidity at air velocities from 0.5 to
3.0 m s
-1
Reference Side weight (kg) Air velocity (m s
-1
)
0.5 0.75 1.0 2.0 3.0
Kerens and Visser 105 19.5 18.5 18.0 16.0 14.8
(1978)
Kerens and Visser 140 24.1 22.8 21.8 19.7 18.5
(1978)
Bailey and Cox 140 27.2 – 25.0 22.1 20.0
(1976)
lean and heavy animals fat. Comparisons can thus only be made over a
limited weight range. In the Langford work (Bailey and Cox, 1976) using
140 kg sides in air at 0 °C, 0.5 m s
-1
, cooling times of the fattest carcasses were
as much as 20% above the average and the leanest 20% below. In South
Africa (Kerens and Visser, 1978) cooling times at 0°C, 0.75 m s
-1
for fat and
lean sides of 100 kg were 24.5 and 19.0h, respectively, and for 125 kg, 27 and
22 h, respectively.
6.2.1.2 Effect of environmental and carcass variables on weight loss
Weight loss is governed by the same variables that affect cooling rate but
with different relative importance.
6.2.1.2.1 Air temperature
The effect of air temperature on evaporative weight loss during chilling is
dependent upon the criteria used to define the end of the chilling process
(Fig. 6.5). When chilling for a set time (18h) weight loss increases as tem-
perature decreases. The opposite effect is found when chilling to a set
temperature (10 °C in deep leg) with weight loss decreasing as the air
temperature is lowered. However, the magnitude of the effect of air tem-
perature on weight loss is small, as a reduction in air temperature from 4
to 0°C produces a change of <0.1% (Fig. 6.5) under either criteria.
6.2.1.2.2 Air velocity
The effect of air velocity is similar to that of air temperature. An increase
from 0.5 to 3.0 m s
-1
made <0.1% difference to losses when sides were
chilled to a deep leg temperature of 10 °C. Increasing the air velocity from
0.75 to 3ms
-1
raised weight losses by up to 0.2% when measured over an
18 h chilling period (Fig. 6.5). In a longer chilling cycle, the effect would be
even more severe. Hence, there are considerable economic advantages to
be gained in systems where the air velocity is reduced after the majority of
the heat has been extracted from the carcasses (Gigiel and Peck, 1984).
From this time on, the rate of cooling is then determined by thermal con-
ductivity of the meat and not by the heat transfer coefficient at its surface.
In Australia, the Meat Research Corporation (1995) recommends the use
of infrared thermometry to automate this process. If the room is also
Primary chilling of red meat 105
Table 6.2 Chilling time (in h) to 7 °C in the deep leg of 50–220 kg beef sides in
air at 0 °C, 0.75 m s
-1
(source: Kerens and Visser, 1978) or 0 °C, 1.0 m s
-1
Conditions Side weight (kg)
50 75 100 140 180 220
0 °C, 0.75 m s
-1
13.0 17.6 21.6 27.4 – –
0 °C, 1.0 m s
-1
– – 25.6 30.9 36.0 42.1
Source: Bailey and Cox, 1976.
operated as a storage chill, for example over weekends, the need to operate
at low air velocities to reduce weight loss and subsequent surface dis-
colouration is even more important.
6.2.1.2.3 Relative humidity
Relative humidity has a greater effect on weight loss than either air tem-
perature (see previously) or velocity (Fig. 6.5). Reducing relative humidity
from 95 to 80% increased evaporative weight loss over an 18 h chilling cycle
at 0 °C by nearly 0.5%.
6.2.1.2.4 Side weight
Percentage evaporative weight loss decreases as side weight increases
(Table 6.3), the effect being marked at very low side weights (<100kg), but
far less so at and above the average side weight for the UK (135 kg).
6.2.1.2.5 Fat cover
It is clear from Fig. 6.5 that fat cover has a substantial effect on evapora-
tive weight loss during an 18h chilling period. In the worst circumstances a
very lean side with little or no fat cover can lose almost 1% more than sides
of similar weight with a thick even covering of fat.
106 Meat refrigeration
3.0
1.5
75 80 85 90 95
0.75
Air speed m s
–1
Relative humidity (%)
2.0
2.5
W
eight loss (%)
Fig. 6.5 Weight loss during 18 h chilling at an air temperature of 0 °C at different
velocities and relative humidities (source: James and Bailey, 1990).
6.2.1.2.6 Operational factors
Investigations have been carried out in a commercial chiller that was
designed to operate in either (1) a slow chilling mode to avoid cold short-
ening or (2) a rapid chilling mode for a quick turnover and reduced weight
loss. The work showed that operational factors are as important as techni-
cal specifications with respect to total weight loss (Gigiel et al., 1989b). Over
50% of the variance in weight loss was accounted for by the difference in
time that elapsed between death and hot weighing, whilst a further 11.8%
was related to the time that elapsed between hot weighing and loading the
beef side into the chiller.
6.2.1.3 Product loads
If specified cooling schedules are to be attained, refrigeration machinery
must be designed to meet the required heat extraction rate at all times
during the chilling cycle. Heat enters a beef chill room via open doors, via
personnel, through the insulation, from lights and cooling fans, and from
the cooling carcasses or sides. The product load is the major component of
the total heat to be extracted from a fully loaded chill room (Collett and
Gigiel, 1986).
The rate of heat release from a single side varies with time. It is at a peak
immediately after loading and then falls rapidly.The peak value is primarily
a function of the environmental conditions during chilling and is not sub-
stantially affected by side weights in the region of 120–140 kg (Kerens, 1981).
In commercial systems, the peak load imposed on the refrigeration plant is
also a function of the rate at which hot sides are introduced into the chill
room. Increasing air velocity, decreasing air temperature or shortening
loading time increases the peak heat load. There is a four-fold difference in
peak load between a chill room operating at 8°C, 0.5 ms
-1
loaded over 8 h
and the same room operating at 0 °C, 3 m s
-1
and loaded over 2 h.
The average product load can easily be calculated by dividing the total
enthalpy change during chilling by the chilling time. The ratios of peak to
average (Table 6.4) and actual to average heat loads (Table 6.5) can be used
both to determine compressor size and ascertain the heat loads during the
later stages of chilling, when compressor off-loading might be required.
Primary chilling of red meat 107
Table 6.3 Effect of side weight on evaporative weight
loss (%) after cooling for 18 and 42 h at 0 °C, 0.75 m s
-1
and 95% relative humidity
Chilling time Side weight (kg)
(h)
50 110 130 150 170
18 2.7 2.0 1.9 1.8 1.7
42 3.6 2.5 2.4 2.2 2.1
Source: Bailey and Cox, 1976.
Peak load data charts have also been produced in South Africa (Kerens,
1981) for two air temperatures (0 and 7 °C), an air velocity of 0.75 m s
-1
and
95% relative humidity. They are expressed in terms of peak heat loss rate
against a loading rate in cattle units per hour. A cattle unit is defined as a
whole carcass and the average whole carcass weight is 210kg. In a typical
South African situation a plant operating at 0°C, 0.75 m s
-1
would be loaded
over a 3 h period at a rate of 200 cattle units h
-1
. The peak heat loss rate
from the 600 carcasses would be 550 kW. It is stated that using three chill
rooms, each with a capacity of 200 carcasses (400 sides), the fan power
required would be 60 kW and the heat infiltration 105kW, of which 90 kW
infiltrates through the doors. Thus, the total peak load on the refrigeration
plant would be 715 kW.
6.2.1.4 Cost of chilling operation
Data were obtained from a survey of 14 commercial beef chilling systems
(Gigiel and Collett, 1990). They ranged in capacity from 18 000 to 93 000 kg
108 Meat refrigeration
Table 6.4 Ratio of the peak to the average rate of heat release from 140 kg beef
sides, for chiller cycle time of 24 h from 1 h post-mortem
Chiller conditions Peak to average ratio
Temperature Loading period
Air speed (m s
-1
)
(°C) (h) 0.5 1.0 2.0 3.0
0 2 3.4 3.3 4.3 4.0
4 2 4.1 3.7 4.3 4.3
0 4 2.9 2.8 3.0 3.0
4 4 3.1 2.7 3.2 3.1
0 6 2.5 2.5 2.5 2.6
4 6 2.7 2.3 2.8 2.7
0 8 2.3 2.5 2.3 2.4
4 8 2.6 2.3 2.4 2.5
Source: Cox and Bailey, 1978.
Table 6.5 Ratio of actual to average heat load ratios for 140 kg beef side in air
at 0 °C, 1.0 m s
-1
, for a chiller cycle time of 24 h from 1 h post-mortem
Time after start Heat load ratios at Time after start Heat load ratios at
of chill (h) end of period shown of chill (h) end of period shown
2 3.3 14 0.6
4 2.3 16 0.4
6 1.5 18 0.4
8 1.2 20 0.4
10 0.8 22 0.3
12 0.7
Source: Cox and Bailey, 1978.
(mean 30 625 kg) of beef in carcass form and in size from 216 to 1124 m
3
.
The energy data were broken down into a base demand and a product
demand (Table 6.6). Base demand is the energy required to maintain the
chiller at the desired temperature with the doors closed. Product demand
is the additional energy needed to reduce the temperature of the meat.
When carcasses are loaded into a chilling system the infiltration of warm
air through the open doors further adds to the load on the refrigeration
plant and this is included in the product load values.
The base demand will depend on the average ambient air temperature,
the level of insulation, the fan power and the control system used. Plant 1
achieved a zero-base demand in the winter because the control system cut
out the fans and compressor when the desired room temperature was
reached. The other plants were controlled such that all the evaporator fans
ran continuously, except during defrosts, resulting in considerable base
demands. To aid comparison, where chillers were not fully loaded, specific
energy consumption for full loading was calculated by multiplying product
demand per kilogram for a partially loaded chiller by its total capacity and
adding this to the base demand.
Approximately 48 h were required in the commercial chillers to meet the
EC requirement of a maximum carcass temperature of 7 °C (Table 6.7) and
side temperatures of up to 17.0 °C were measured on dispatch from one of
Primary chilling of red meat 109
Table 6.6 Average ambient air temperature over survey. The energy used per
kilogram of beef produced divided into the base demand and the product
demand, and *the total energy consumption per kg adjusted to allow for a full
chiller
Chiller Ambient air Base First Second *First *For 48 h
system temperature demand 24 h 24 h 24 h (kJ kg
-1
)
identity (°C) (kJ kg
-1
) (kJ kg
-1
)(kJkg
-1
)(kJkg
-1
)
number
1 4.0 0.0 63.0 5.8 63.0 68.8
2 14.0 35.0 43.0 15.0 78.0 128.0
3 7.5 26.0 62.6 – 86.0 –
4 0.0 15.0 48.0 3.0 63.0 81.0
5 14.0 38.0 42.0 36.0 80.0 154.0
6 19.0 33.0 62.3 5.3 86.0 115.0
7 21.0 56.7 22.6 5.6 67.0 116.0
8 11.0 44.0 42.0 9.0 86.0 139.0
9 0.0 32.0 30.0 14.0 62.0 108.0
10 4.0 26.0 31.8 7.9 52.0 80.0
11 18.0 40.0 62.8 45.8 102.0 187.0
12 10.5 24.0 53.0 – 77.0 –
13 14.0 40.0 47.7 18.8 86.0 143.0
14 18.0 44.0 53.0 9.0 97.0 150.0
Means 32.4 47.4 14.6 77.5 122.5
Source: Gigiel and Collett, 1990.
the chillers. Specific energy consumption for the first 24 h of chilling varied
from 57.8 to 78 kJ kg
-1
in the winter to 78 to 102.8 kJ kg
-1
in the summer.
Substantially less energy was required in the subsequent 24 h ranging from
3.0 to 45.8kJkg
-1
(average 14.1kJkg
-1
).
Weight losses ranged from 1.18 to 2.06% for the first day of chilling and
from 1.45 to 2.31% for 2 days. The cost of this loss was on average 20 times
the energy cost and therefore of greater economic importance. Plant 1 had
the lowest weight loss and energy consumption and achieved a maximum
meat temperature of 5.8 °C after 44 h. It can therefore be used as a target
for chill room design and operation. This target would require a maximum
energy consumption over 48 h of 44kJ kg
-1
in winter, 140 kJ kg
-1
in summer
and a maximum weight loss of 1.5%.
6.2.2 Lamb, mutton and goat chilling
Many conventional chilling systems for lamb carcasses fail to produce
optimal textural qualities or minimum weight losses. No publications have
been found on large scale systematic investigations of lamb chilling that are
similar to those that have been carried out on beef.
110 Meat refrigeration
Table 6.7 Average weight of sides, average air velocity over deep leg, average
chiller temperature over and at end of 24 h, deep leg temperature after 24 h and
when removed from chiller, time of removal from chiller and percentage weight
loss
Chiller Average Air Chiller Side Time of Weight
number side velocity temperature temperature removal loss
weight (m s
-1
)
mean end after on
(h)
after after
(kg)
24 h 24 h 24 h removal 24 h 48 h
(°C) (°C) (°C) (°C) (%) (%)
1 128 0.49 3.0 0.0 10.8 5.8 44.0 1.18 1.45
2 138 0.27 4.0 2.0 10.8 10.8 24.0 1.75 –
3 148 0.90 1.5 0.0 11.9 9.0 26.5 1.36 –
4 178 0.60 3.0 6.0 14.5 8.0 48.0 1.46 1.66
5 152 0.66 8.0 4.0 15.0 12.0 26.0 1.79 –
6.1 145 0.08 3.0 1.0 15.6 3.9 50.0 1.82 –
6.2 137 0.08 3.0 1.0 – – – – 2.31
7 129 0.75 12.5 3.0 17.0 17.0 24.0 1.61 –
8 130 0.40 5.5 1.0 17.5 7.0 48.0 1.66 –
9 163 0.34 9.0 5.0 18.5 8.6 48.0 1.67 –
10 – 0.20 6.0 2.0 19.0 9.0 44.0 1.12 –
11 152 0.41 16.5 7.0 19.8 4.4 48.0 1.89 –
12 154 0.90 7.0 2.0 20.0 14.5 32.0 1.43 –
13 142 0.33 6.0 4.0 – – – 2.06 2.3
14 – 0.75 10.0 3.0 – – – – –
Means 146 0.48 6.5 2.7 15.9 9.2 38.5 1.6 1.93
Source: Gigiel and Collett, 1990.
In beef sides the heat capacity and thickness of the carcasses makes it
very difficult to reduce the internal temperature of the meat, to a value suit-
able for cutting or transportation, within a 24h cooling cycle. Lamb and
mutton carcasses are much smaller and rapid cooling rates can be achieved.
However, it has been known for many years that reducing the temperature
of the muscles in either beef or lamb to below 10°C within 10 h post-
mortem is likely to increase the toughness of the meat when cooked owing
to a phenomenon called ‘cold shortening’ (see Chapter 3). Many experi-
mental investigations have been carried out to determine the extent of
toughening under different cooling conditions and ways of alleviating the
condition by either a delay period (Anon, 1975) or electrical stimulation
(Crystal, 1978). In commercial operation, a chilling system needs to be
designed and operated to chill efficiently while maintaining meat quality.
In order to achieve this objective, the designer must have information about
the environmental conditions that are necessary to meet any given meat
temperature specification, and the effect of these conditions on the cooling
rate, weight loss, microbiology, appearance and acceptability of the product.
Most lamb carcasses chilled in the EU have to have a maximum inter-
nal temperature of 7°C, before cutting or transport. Some abattoirs would
like to dispatch lamb on the day of slaughter and to meet this requirement,
chilling has to be complete in 8–10h. For others overnight chilling in 14–
16 h is normally desired.
6.2.2.1 Effect of environmental and carcass variables on cooling rate
The temperature of the air and its velocity over the surface of the carcass
are the two main environmental factors governing the rate that heat can be
extracted from a sheep carcass. Carcass weight and fat cover control the
amount of heat that has to be extracted and its rate of conduction to the
surface.
Published data from a number of sources on chilling time is presented
in Table 6.8 and Table 6.9 and discussed in the following sections.
6.2.2.1.1 Air temperature and velocity
Earle and Fleming (1967) found that reducing the air temperature used
during chilling from 4 to 0 °C results in approximately a 25% reduction in
chilling time to 7 °C in the deep leg of carcasses ranging in weight from 12
to 33kg.
No data have been located that examine the effect of air velocity on the
chilling rate of lamb or mutton carcasses, but those produced for goats of
20 kg (Gigiel and Creed, 1987), which have a comparable chilling time, show
a large effect. In air at 0 °C, increasing the air velocity from 0.5 to 1m s
-1
reduces the chilling time to 7 °C in the deep leg from 10 to 8 h and further
increasing the velocity to 3 m s
-1
results in a time of 5 h.
Chilling in air at 0 °C, 1.0 m s
-1
will achieve a chilling time to 7 °C of 10 h
for carcasses up to 30 kg in weight, which will allow for dispatch on the same
Primary chilling of red meat 111
day as slaughter in many abattoirs. Reducing the initial temperature to
-2 °C, and increasing the air velocity to 3.0m s
-1
resulted in a 6h chilling
time with lighter 15–17.5 kg lamb carcasses without any surface freezing.
Neglecting other constraints, imposed by eating quality considerations,
severe environmental conditions are not required to produce chilling times
that allow cutting or transport on the same day as slaughter. Air tempera-
tures of, or slightly less than the desired final meat temperature in the range
0–4 °C, and a low air velocity 0.2–0.5 m s
-1
will achieve overnight chilling in
14–16h.
6.2.2.1.2 Carcass weight and fat cover
As with beef, it is difficult to separate the effect of carcass weight from fat
cover on chilling time. Little difference was observed in the cooling times
112 Meat refrigeration
Table 6.8 Environmental conditions, carcass weight and cooling times (h) in
different parts of carcass
Air conditions Weight Position Temp Time Position Temp Time
Temp °C speed
(kg)
(m s
-1
)
0 0.15 12 Deep leg 7 6.5 Deep leg 2 10.0
25 7 7.2 12.0
25 7 8.4 14.0
28 7 10.4 17.0
33 7 15.0 23.0
4 0.15 12 Deep leg 7 8.6
25 7 10.0
25 7 12.0
28 7 14.3
33 7 20.0
1 0.5 30 Deep leg 7 10.0 Deep loin 7 7.0
Surf. leg 7 7.0 Surf. loin 7 5.0
6 h at 15 0.1
then 1 0.5 30 Deep leg 7 13.0 Deep loin 7 10.0
Surf. leg 7 9.0 Surf. loin 7 7.0
7 h at -2 3.0 15 to 17.5
then 0 0.1 Deep leg 10 4.2 Deep loin 10 2.5
Deep leg 7 6.0 Deep loin 7 3.5
Source: Swain and James, 1988.
Table 6.9 Cooling time to 7 °C and 1 °C in deep M.
longissimus dorsi in air at 1 ± 1 °C for lamb carcasses of
different average weights and fat covers
Carcass weight (kg) 26.8 21.5 16.8
Fat thickness 12th rib (mm) 7.1 3.3 1.1
Cooling time to 7 °C (h) 4.3 3.1 1.9
Cooling time to 1 °C (h) 8.1 5.9 5.6
Source: Smith & Carpenter, 1973.
in the deep longissimus muscles of 29.6–30.3 kg ram carcasses with high and
low fat thicknesses (Kadim et al., 1993). The ram carcasses were initially
held for 100 ± 5 min at 15–20 °C then cooled in air at 1–3 °C. When the fat
was completely stripped from the muscle, the cooling time to 7 °C was
reduced from 10 to 8 h.
However, the chilling time to 7 °C in the M. longissimus dorsi of lean
light (16.8 kg) lambs can be under half that of 26.8 kg lambs with a much
thicker fat covering (Table 6.9). It would not be unusual for a chilling system
to contain lamb carcasses covering this range of weights and fat covers. The
design and operation of such a system must therefore be a compromise
between overlong chilling periods for the smaller carcasses and undercool-
ing of the larger carcasses.
6.2.2.2 Effect of environmental and carcass variables on weight loss
Experiments carried out at Langford showed that a lamb carcass has lost
ca. 2.5% of its hot weight at 24 h post-mortem after chilling and the initial
phase of storage and after a further 5 days in the chill room this loss has
risen to over 4%. Losses of this magnitude are therefore of considerable
economic consequence to a meat wholesaler. The environmental and
carcass factors that affect weight loss include those that affect chilling time
with the addition of the relative humidity of the air.
6.2.2.2.1 Air temperature, velocity and relative humidity
The rate of loss of moisture from a saturated surface into an air stream
passing over it is a function of the surface area, mass transfer coefficient
and the vapour pressure difference between the surface and the air. Any
decrease in relative humidity increases the total weight loss, and within the
temperature range (0–10°C) found in commercial chill rooms, a 20% reduc-
tion in relative humidity will increase weight loss by at least 0.2%.
Weight loss increases as chilling temperature decreases. However, this
fact must be considered in context with the data already presented on chill-
ing time. After 6 h in air at 0 °C, a 15 kg lamb carcass would be substantially
cooled and after a few more hours it could be either cut or dispatched. At
25 °C, less than 40% of the required heat would have been extracted and a
substantial further time at a lower temperature would be required before
the carcass could be further processed. During this time the carcass would
continue to lose weight.
A similar complication occurs with the effect of air velocity on weight
loss (Table 6.10). If the carcass is to be removed from the chilling system
immediately after a maximum internal temperature has been achieved, then
increasing the air velocity will result in a lower weight loss. However, if a
set time is allowed for the chilling process then the minimum weight loss is
likely to be achieved by using the minimum air velocity that will result in
the desired amount of heat being extracted in the time available.
Primary chilling of red meat 113
In all cases, the air humidity should be maintained at the highest level
that can be economically justified.
6.2.2.2.2 Carcass weight and fat cover
The rate of weight loss is proportional to surface area and the surface area
to volume ratio becomes less as the weight of a carcass increases. Percent-
age weight loss should therefore decrease as carcass weight increases. In a
test using 300 carcasses in the same chilling system (Smith and Carpenter,
1973) the lightest carcasses lost 3.14% and the heaviest 2.95% over 72h
(Table 6.11) but the difference was not significant (P > 0.05).
In the same tests, a maximum increase in weight loss of 0.26%, over
72 h chilling and storage, was found between lambs with low areas of fat
cover and those with almost complete fat cover. Further investigations
involving almost 700 carcasses in three chill rooms showed that increasing
fat thickness reduced weight loss by up to 1.12% over 72 h.
6.2.2.3 Quality considerations
Toughening caused by cold shortening (see Chapter 3) will occur in lamb
if the meat falls below 10°C within 10h post-mortem (Rhodes, 1972). As
the rate of temperature reduction increases, the amount of cold shortening
increases. The longer the delay between slaughter and the reduction of any
114 Meat refrigeration
Table 6.10 Percentage weight loss from 15 ￥ 15 ￥ 2 cm thick samples of lean
mutton cooled from one side in air at 1–2 °C, for a set time or to a set maximum
internal temperature, at different air velocities
Air velocity (m s
-1
) Cooling time (h) Final temperature (°C)
422137 4
3.7 1.64 4.11 0.95 1.14 1.27
1.4 1.60 3.25 1.09 1.32 1.48
0.6 1.67 3.03 1.20 1.49 1.69
Source: Lovett et al., 1976.
Table 6.11 Percentage weight loss from lamb carcasses in different weight
ranges chilled and stored in air at 2 ± 1 °C, 90% relative humidity for 72 h
Carcass weight range (kg) No of carcasses Weight loss after 72 h (%)
<22.4 32 3.14
22.5–24.7 87 3.08
24.8–26.9 74 2.99
27.0–29.2 55 3.10
>29.3 52 2.95
Source: Smith & Carpenter, 1973.
part of the musculature on the carcass to below 10°C, the less the degree
of shortening that will occur. All the musculature of a 30kg lamb carcass
that is chilled sufficiently to meet the EEC legislation and to be dispatched
on the same day as slaughter will be cold shortened.
Delaying cooling by hanging the carcass at a temperature of ca. 15°C for
6 h and then chilling at 1°C, 0.5 m s
-1
, will avoid the risk of cold shortening
in the major parts of the leg and loin (Taylor et al., 1972). The process will
achieve a total chilling time to 7°C of 13h. Recommendations from New
Zealand (MIRINZ, 1985) state that meat held at 10 °C for 16–24 h (condi-
tioned) and then rapidly chilled and frozen is only moderately tender.
Holding the carcass, after conditioning, in a chilled state for three days will
increase the percentage of acceptably tender meat in the loin from 64 to
90%. Nearly the same degree of tenderness can be achieved using high
voltage electrical stimulation in an accelerated conditioning and ageing
process. The carcass is either stimulated at less than 5 min post-mortem
(predressing) for 45 s or for 90s at less than 30min post-mortem (post-
dressing). It is then held at a temperature above 6°C for at least 8h before
being chilled to 0–2 °C for cutting or transportation.
6.2.3 Pork
Conventional pig chilling systems aim to reduce the mean temperature of
the side or carcass to ca. 4 °C, a temperature considered suitable for cutting
or curing. Most producers despatch, cut or commence further processing of
the chilled carcass on the day after slaughter, allowing a period of 14–16 h
for the chilling operation. Different markets for pig carcasses are defined
in terms of weight ranges (Table 6.12).
Many pig slaughterhouses concentrate on a limited range of weights,
some specialising in pigs for one type of further processing such as bacon
production, while only a few handle the total weight range. Experimental
studies at Langford investigated the relationship between air temperature
and velocity and rates of cooling in pig carcasses covering a weight range
from 40 to 150 kg.
Primary chilling of red meat 115
Table 6.12 Market weight ranges for pig carcasses
Group Carcass weight (kg)
Porkers <50
Cutters 50–67.5
Baconers 58.5–76.5
Heavy cutters 68–81
Heavy hogs >81.5
Source: Kempster et al., 1981.
6.2.3.1 Effect of environmental and carcass variables on cooling rate
6.2.3.1.1 Air temperature and velocity
Mean cooling curves, together with 95% confidence limits, for 40, 60, 80, 100
and 150kg carcass weights in air at 0, 4 and 6°C have been produced for
various air velocities such as 0.5 m s
-1
, 1.0ms
-1
and 3.0ms
-1
(Brown and
James, 1992). A deep leg temperature of 7°C is required by EC regulations
before the transport or cutting of meat for export. A 40 kg carcass would
require ca. 13 h in air at 4 °C and 0.5 m s
-1
. A 4 °C reduction in air tempera-
ture to 0 °C will decrease the cooling time by 3h to slightly under 10h. To
achieve the same reduction whilst maintaining the air temperature at 4 °C
the air velocity would have to be increased from 0.5 to 3.0 m s
-1
.
6.2.3.1.2 Carcass weight
Table 6.13 gives the heaviest pig carcasses that can be cooled to a deep leg
temperature of 7°C by 16 h post-mortem. In the experimental situation
the carcasses were placed in the cooling chamber at 50 min post-mortem,
the temperature pull-down period was minimal (less than 30 min) and the
air velocity was maintained over all the surfaces of the carcasses. Few if any
of these conditions would be achieved in commercial practice and the
weights should therefore be taken as a theoretical upper limit to the weights
that could be cooled.
6.2.3.2 Product loads
The thermal load released by a pig carcass during a conventional chill
has been measured for a particular set of chilling conditions (Lang, 1972).
The rate of heat release will depend not only on carcass and environmen-
116 Meat refrigeration
Table 6.13 Maximum weight of pig carcass that can be
cooled to 7 °C in deep leg within 16 h at different
combinations of air temperature and velocity
Chill room air Heaviest carcass cooled to
Temperature Velocity
7 °C in deep leg in 16 h
(°C) (m s
-1
)
(kg)
0 0.5 100
1.0 105*
3.0 110*
4 0.5 60
1.0 80
3.0 95*
6 0.5 <40
1.0 40
3.0 60
*Interpolated values
Source: Brown and James, 1992.
tal factors but also the loading pattern for the chiller. Data are provided on
the decline in product load from peak to average and below. It is expressed
in the form of % of heat released per h of chilling.
The total heat released (Q) can be calculated by:
[6.2]
where m = mass of carcass in kg, C
p
= specific heat in kJ kg
-1
°C
-1
and DT =
temperature reduction of carcass in °C. The way in which this heat is
released can then be determined using the percentages for each pig enter-
ing the chillroom.
6.2.3.3 Cost of chilling operation
A survey of five pig chilling operations in the United Kingdom highlighted
some of the problems inherent in conventional chilling systems (Gigiel,
1984; Collett and Gigiel, 1986). See Table 6.14 and 6.15. All the plants
QmCT= ()
p
kJD
Primary chilling of red meat 117
Table 6.14 Environmental conditions and loading in five commercial pork
chilling systems
Plant Hot weight Total pigs Chill room Air velocity Air temp
no. of pigs in room capacity
av. max. min.
at end of
average total
(no.) (no.)
(m s
-1
)
chilling
(kg) (kg)
(°C)
1 42.7 3 245 76 200 1.5 2.2 0.2 6
2 63.9 29 713 465 465 0.5 1.3 0.2 1
3 64.8 14 714 227 270 0.5 1.0 0.3 2
4 67.0 21 440 320 500 0.2 0.5 0.2 5
5 64.1 22 249 375 780 0.8 4.4 0.5
Second stage 500 0.7 1.8 0.2 3
Source: Collett and Gigiel, 1986.
Table 6.15 Energy demand, consumption and product
weight loss during commercial chilling
Plant Base Product Total energy Weight
no demand demand in consumption loss
(MJ) full room in full room (%)
(MJ) (kJ kg
-1
)
1 778 378 208 3.50
2 1728 1624 112 2.60
3 781 648 89 2.17
4 1332 1206 96 1.85
5 3658 2371 258 2.06
Mean 1655 1245 153 2.44
Source: Collett and Gigiel, 1986.
surveyed used an overnight chilling operation so that the pork carcasses
were ready for cutting or dispatch on the day after slaughter. The air tem-
perature in the four single stage systems rose substantially to a maximum
of 19 °C in plant 1, after they were loaded with freshly slaughtered carcasses,
and still ranged from 1 to 6 °C at the end of the chilling process. During
loading the energy consumption of the refrigeration plant was typically over
2.5 times the average consumption throughout chilling. The plant operated
at full capacity for 4 h until the peak rate of heat release had been over-
come and it was able to start reducing the air temperature to its designed
level.
Air velocities over the surface of the hind legs of carcasses varied
considerably both within (<0.2–2.2ms
-1
) and between chill rooms
(<0.2–1.5ms
-1
).
In normal operation the base energy demand, i.e. the amount of energy
required to run the empty closed chill room at its design temperature, was
57% of the total energy consumption during the chilling operation. The
energy cost of the chilling operation per kilogram of pork chilled was there-
fore dependent on the utilisation of the chill room. The average cost of the
evaporative weight loss during the chilling period was a factor of 15 higher
than the energy costs.
The data gathered in this survey revealed large variations in the perfor-
mance of commercial chilling plants and a lack of complete chilling in a
number of situations. Variation in weight loss was substantial, although
the mean agreed well with the national average of 2.27% (Kempster et al.,
1981). Chiller number 4 produced the lowest overall cost and since it had
no novel features, provides a target of 96 kJkg
-1
for energy consumption
and a 1.85% weight loss for a fully loaded chill room against which all pork
chill rooms can be compared. The survey did not provide any direct process
design data to aid in the specification of new chilling systems.
6.2.4 Chilling of offal
There appears to be little published data on the chilling of offal. Stiffler et al.
(1985) and Vanderzant et al. (1985) investigated the effect of five chilling
treatments on weight loss and bacterial and sensory changes after storage
and transportation. The five regimes used: (1) air at 2 °C for 24 h, (2) air at
2°C for 4–6h, (3) air at -20 °C for 2h, (4) air at -20°C for 0.5–1h and (5)
slush ice for 2 h. Significant differences in weight loss were measured after
chilling with the faster treatments using air at -20 °C or immersion tending
to produce the lowest losses (Table 6.16). After storage and transportation,
there was usually no significant difference in weight losses between treat-
ments or with the non-prechilled control. Bacterial counts after transport
were usually lower on samples that had been prechilled before packaging.
However,off-odour scores of non-prechilled vacuum packed samples of beef
livers, pork tongues, lamb livers and lamb tongues were lower than compa-
rable samples that had received an initial chilling treatment.
118 Meat refrigeration
6.3 Novel systems with future potential
The previous section has outlined a number of obvious problems with con-
ventional chilling operations. These include long chilling times, variable
chilling, batch operation, uneven product loads and high weight losses.
Many alternative systems have been investigated to overcome some if not
all of these problems.
6.3.1 Accelerated chilling systems
6.3.1.1 Beef
Using conventional single stage chilling regimes it is evident that only rel-
atively light, lean beef sides can be cooled to 7°C in the deep tissue during
a 24 h operating cycle, whilst evaporative losses are of the order of 2%.
There is considerable interest in methods of shortening cooling times and
reducing evaporative weight loss. All accelerated cooling systems are likely
Primary chilling of red meat 119
Table 6.16 Percentage weight loss after different chilling treatments and after
storage and transportation
Treatment % Weight loss
1234 5Control
After chilling
Beef
Liver 2.51 1.49 1.13 1.12 – –
Heart 1.56 1.39 1.35 0.69 – –
Tongues 1.53 1.25 1.05 0.42 – –
Kidneys 1.59 1.37 1.33 0.63 – –
Pork
Liver 1.72 – 0.97 – -0.98 –
Heart 1.93 – 1.11 – -1.99 –
Tongues 0.62 – 0.00 – -1.89 –
Kidney 0.69 – 0.63 – – –
After storage and transport
Beef
Liver 5.48 5.36 6.65 5.35 – 3.97
Heart 3.87 2.47 3.55 2.74 – 5.07
Tongues 1.46 1.29 1.21 0.92 – 0.23
Kidneys 1.65 1.63 1.56 1.46 – 0.11
Pork
Liver 3.33 – 4.79 – 2.59 2.45
Heart 5.79 – 5.66 – 3.64 6.11
Tongues 4.00 – 2.89 – 1.37 2.13
Kidney 1.87 – 1.78 – – 1.03
Source: Stiffler et al., 1985.
to be more expensive to install and operate than conventional plants.There-
fore, to be cost effective they must offer substantial savings in terms of
increased throughput and/or higher yields of saleable meat.
Attempts have been made to reduce cooling times by increasing the
surface heat transfer coefficient, for example, by using radiative plates in
conjunction with blast air (Gerosimov and Malevany, 1968; Gerosimov and
Rumyanstev, 1972). However, most accelerated chilling systems rely on the
maintenance of very low temperatures (-15 to -70 °C) during the initial
stages of the chilling process. This can be achieved either by powerful
mechanical refrigeration plant (Kerens, 1983; Watt and Herring, 1974;
Sheffer and Rutov, 1970; Union International Consultants, 1984) or by cryo-
genic liquids (Kerens, 1983; Watt and Herring, 1974; Bowling et al., 1987).
The factors governing the evaporative loss from sides chilled at sub-zero
temperatures are the same as those from meat chilled in conventional
systems. The rapid drop in surface temperature of the side when chilling at
very low temperatures not only limits evaporation from the surface but also
leads to crust freezing. This frozen crust acts as a vapour barrier inhibiting
further evaporation.
Any substantial freezing would produce increased drip loss on final
cutting (Gigiel et al., 1985). To avoid this, accelerated systems only maintain
very low temperatures during the first few hours of the chilling process.
One or more successive stages at progressively higher temperatures are
employed, with the final stage at or above 0°C either to remove the last of
the heat or to allow for temperature equalisation. However, in one report
(Anon, 1985), where chilling was carried out at -70°C for 5h and the inte-
rior of the loin had reached 0 to -2 °C at the end of this period, a substan-
tial amount of freezing must have occurred.
Data on cooling times, environmental conditions, weight losses or savings
in weight loss where comparisons have been made with conventional
carcass chilling systems are given in Table 6.17. All the accelerated chilling
systems offer substantial increases in yield, 0.4–1.37% and the majority cool
all but the heaviest sides to below 7°C in under 18 h, to achieve a 24h pro-
cessing cycle. Little information is provided on the amount of crust free-
zing that occurred during the chilling operations or any textural problems
caused by the rapid rates of temperature fall. Considerable surface fre-
ezing occurred in all the experiments carried out at Langford (Union
International, 1984; James; unpublished). All of those carcasses had been
subjected to high voltage electrical stimulation before chilling to avoid cold
shortening, and instrumental tests failed to reveal any significant difference
in texture between rapidly chilled and control sides.
Despite the considerable number of trials that have taken place and the
cost advantages shown in feasibility studies (Union International Consul-
tants, 1984; Bowater, 2001), no commercial plants are believed to have
resulted from the work, with the possible exception of some systems in the
former Soviet Union.
120 Meat refrigeration
6.3.1.2 Lamb
The New Zealand specification for lamb carcasses requires a holding time
of 90 min after stimulation before being subjected to temperatures below
6 °C. Some processors would like to chill their carcasses much more rapidly
with the aim of reducing the need for cooling floor space or to firm
the carcass prior to cutting. Research by Davey and Gilbert (1973) and
Davey and Garnett (1980) suggested that rapid chilling of lamb was pos-
sible in certain circumstances without cold shortening. MIRINZ (1986/
87) have carried out investigations on the possibility of using very low
temperatures (-25 or -30 °C) for a short period of 30 min followed by an
equalisation period at 0 °C until the deep leg temperature reaches
7 °C. The treatment produced a 4h process from slaughter to deep tem-
perature of 7 °C. The products, which are then fast frozen, are claimed to
be moderately tender.
Primary chilling of red meat 121
Table 6.17 Beef side weights, time to reach a maximum meat temperature of
7 °C, total cooling time, weight loss and savings over conventional chilling systems,
and conditions used in accelerated chilling systems
Conditions Side weight Time (h) Weight loss (%)
(kg)
to 7 °C Total Savings Total
1 50 11 18 0.78 1.47
100 18 18 average 3 weights
150 24 –
2 123 15 20 – 0.88
3 119 14 21 – 1.03
4 118 13 21 1.03 1.12
5 – – – 0.4–0.5 –
6 – – 10–16 1.0 1.0
7 – 14 21 0.66 1.28
8 125 – 21 1.37 1.36
9 120 20 21 0.44 1.08
10 – – 24 0.90 0.43
The chilling conditions are:
(1) 3 h at -30 °C with liquid nitrogen injection then gradually rising to 0 °C over 4 h and
remaining at 0 °C.
(2) 3 h at -19 °C, 1.2 m s
-1
followed by 17 h at 0.6 °C, 0.75 m s
-1
.
(3) 3 h at -19 °C, 1.2 m s
-1
then air gradually rising to 0.7 °C over 7 h with air at 0.75 m s
-1
and
remaining at same conditions.
(4) 2.5 h at -19.5 °C, 1.2 m s
-1
; 3 h at -9.5 °C, 0.75 m s
-1
then rising to 0 °C.
(5) 4 h at -29 °C with liquid air.
(6) 4–8 h at -15 to -10 °C, 1–2 m s
-1
then 6–8 h at -1 °C, 0.1–0.2 m s
-1
.
(7) 6 h at -15 °C, 0.5–1.5 m s
-1
, then air gradually rising to 4 °C over 12 h.
(8) 1 h at 15 °C, 2 m s
-1
; 3 h at -12 °C, 2 m s
-1
then 17 h at 4 °C.
(9) 6 h at -15 °C, 2.3 m s
-1
, then 15 h at 0 °C, 0.5 m s
-1
.
(10) 5 h at -70 °C, then 16 °C for 4 h and then at 1 °C for 15 h.
Source: James and Bailey, 1990.
Sheridan (1990) reported that meat from lambs chilled at -20 °C,
1.5ms
-1
for 3.5h was as tender after 7 days ageing as that from lambs
conventionally chilled at 4°C. After 24 h the very rapidly chilled carcasses
had lost 0.8–0.9% less in weight.
6.3.1.3 Pork
Chilling in two stages, with the first stage consisting of a conveyorised
air blast tunnel is quite common (Cooper, 1972; Wernburg, 1972). The
prechiller serves two requirements in that it rapidly lowers the surface tem-
perature, reducing the rate of evaporative weight loss, and has the capacity
to absorb the initial peak heat load. Studies (James et al., 1983; Gigiel and
James, 1984) have shown that all the required heat can be extracted from
a pig carcass or side in a single short blast chilling operation. Immediately
after chilling, the carcass can be band sawn into primals and stored or trans-
ported on the same day as slaughter.
After a 4 h chilling process at -30°C, 1.0ms
-1
, the average temperature
in the primal joints from sides ranged from -1.9 °C in the loin to 1.2 °C in
the shoulder and in whole carcasses from -2.1°C in the belly to 3.0°C in
the shoulder. The average maximum temperatures, recorded at the end of
the 4 h process in the 3 most commercially important joints, were for sides
and whole carcasses respectively, shoulder 10.7 and 18.6°C, loin -1.9 and
2.0°C and leg 14.6 and 14.6 °C.
Evaporative loss was reduced to 1.13% for sides and 1.10% for whole
carcasses, almost half that in the controls (Table 6.18). No extra drip was
measured from the primal joints but the chops from the sides that had been
partially frozen during the process recorded higher drip levels.
Instrumental measurements of texture carried out on loin chops from
ultra-rapidly chilled pork stored for 2 days showed that the meat was
tougher than that of the controls (Table 6.18). There was less increase in
toughness in sides subjected to ultra-rapid chilling than whole carcasses.
After chilling, cutting and 2 days storage in vacuum packs there was no sig-
nificant difference between counts from ultra-rapid chilled material and the
controls.
122 Meat refrigeration
Table 6.18 Mean evaporative and drip losses from ultra-rapid and
conventionally chilled pork, and work done in shearing cooked samples
Side Whole carcass
Evaporative loss (%) 1.13 (-0.85)
?
1.10 (-1.01)
?
Drip in vacuum pack (%) 0.20 (0.00) 0.20 (0.00)
Drip in retail packs (%) 2.31 (+1.32)
?
0.86 (+0.20)
Work done shearing samples (J) 0.18 (+0.02)* 0.21 (+0.05)
?
Difference significant at
?
P < 0.001, * P < 0.05.
Figures in brackets are differences between treatment and control.
Source: James et al., 1983.
6.3.2 Spray chilling
6.3.2.1 Beef
An alternative system in the USA that seems to be rapidly gaining com-
mercial acceptance for beef, is spray chilling (Anon, 1985; Heitter, 1975;
Allen et al., 1987; Johnson et al., 1988). Practical spray chilling systems
have used a combination of air and sprays for the initial part of the chill-
ing period and then air only for the rest of the chilling cycle. The sprays are
not applied continuously but in short bursts, 90 s at 15min intervals for the
first 8 h in one system (Allen et al., 1987) and 30s at 30 min intervals for the
first 12 h in another (Hamby et al., 1987). Cooled water at 2–3°C is used in
the sprays and in the latter a total of 11 litres was delivered from 11 nozzles
over the 30 s period (Hamby et al., 1987). Studies carried out in Canada
(Jones and Robertson, 1988) used 1 min sprays every 15min for either 4, 8
or 12 h with shrouded sides or 8 h with unshrouded sides. Further studies
concentrated on 1 min sprays every 15 min for 10 h with shrouded sides
(Greer et al., 1990).
The main advantage claimed for the system is a reduced weight loss mea-
sured over 24 h that can range from ca. 0.5 to 1.5% (Table 6.19). After 6
days, small but industrially significant reductions in weight loss were
reported for shrouded sides sprayed for 12h and the unshrouded sides
(Jones and Robertson, 1988). After 7 days the weight loss from the 10h
shrouded treatment was 0.41% less than that from controls (Greer et al.,
1990). Cooling rates were faster in the spray cooling systems with deep
temperatures typically 1–2 °C lower than controls. This was caused by the
higher rates of heat transfer and the heat extracted to evaporate the added
water.
Surface drying is often considered an important factor in limiting micro-
bial growth. If the surface remains wet there may be microbial problems
that shorten shelf-life. The addition of lactic or acetic acid has been found
Primary chilling of red meat 123
Table 6.19 Weight loss (%) and saving over conventional chilling produced by
different spray cooling systems
Reference Treatment Weight Saving
loss (%)
(24 h)
Allen et al., 1987 90 s at 0.25 h for 8 h 0.32 1.16
Jones & Robertson, 1988 60 s at 0.25 h for 4 h (shrouded) 1.15 0.48
Jones & Robertson, 1988 60 s at 0.25 h for 8 h (shrouded) 0.60 0.69
Jones & Robertson, 1988 60 s at 0.25 h for 12 h (shrouded) 1.15 0.48
Jones & Robertson, 1988 60 s at 0.25 h for 8 h (unshrouded) 0.35 1.43
Greer et al., 1990 60 s at 0.25 h for 10 h (shrouded) 0.28 1.05
Lee et al., 1990 60 s at 0.25 h for 8 h (shrouded) 0.53 0.72
Lee et al., 1990 60 s at 0.25 h for 8 h (unshrouded) 0.44 1.29
to reduce bacterial contamination (Hamby et al., 1987). However, no dif-
ferences in bacterial numbers were found on sides after 7 days ageing or
on vacuum packed meat after 70 days in storage (Greer et al., 1990).
There is little evidence that spray chilling has any adverse effects on meat
quality. In some spray cooled sides fat colour was significantly lighter than
in controls (Hamby et al., 1987), but Greer et al. (1990) found no differences
in colour. Lee et al. (1990) found no differences in tenderness or juiciness
of meat from spray or conventionally chilled carcasses.
6.3.2.2 Pork
Work carried out in the UK (Dransfield and Lockyer, 1985) and Denmark
(Moller and Vestergaard, 1987) has shown that a short delay period before
the start of chilling improves the texture of pork. However, during this
period the rate of weight loss is highest so yield is likely to suffer. With
spray cooling, the surface remains wet giving maximum mass transfer and
evaporative cooling effect, with no penalty in increased weight loss.
Consequently, combining a spray system with the delay period offers a
way of producing high quality pork without excessive weight loss.
Spray chilling was examined experimentally (Gigiel et al., 1989a) as a
two-stage process (air at 10 °C, 98% RH and 0.7 m s
-1
for 2 h followed by air
at 4 °C, 97% RH and 0.3m s
-1
for 21 h) using sprays of 250ml of water every
20 min for the first 6h of chilling. Controls were chilled in air at 4°C, 92%
RH and 0.3 m s
-1
for 23 h. Achieving the same time to 7 °C, the spray treat-
ment reduced weight loss by 1.22% (Table 6.20).
Both the chilling regimes reduced the total viable counts of bacteria and
there were very small (less than 1log cycle) but statistically significant dif-
ferences between some treatments in counts measured on the medial
surface of carcasses. There were no significant differences in drip loss
between treatments. Jeremiah and Jones (1989) found that spray chilled
pork had to be stored in vacuum packs for 42 days before they measured
any difference in drip between the samples and conventionally chilled con-
trols. They noted a non-statistically significant trend for spray cooled pork
to have a shorter display life.
Commercial spray chilling plants for pork have now been installed in
France and the Netherlands but none currently operate in the UK.
124 Meat refrigeration
Table 6.20 Spray chilling results
Treatment Weight loss Drip Cooling time to 7 °C Texture
(%) (%) (h) (J)
Delay + spray 0.95
a
0.97 17.7 0.196
Conventional 2.17
b
1.55 17.7 0.214
Values within columns with different superscripts a and b are significantly different (P < 0.05).
Source: Gigiel et al., 1989a.
6.3.2.3 Lamb
Heitter (1975) showed that chlorinated water sprayed on the carcass during
chilling produced lower bacterial counts (reductions of 94.5–99.5% in
viable counts), lower evaporative weight loss (up to 1.25%) and quicker
cooling rates.
Brown et al. (1993) developed two spray chilling treatments to improve
appearance and reduce weight loss during lamb chilling. The first treatment
was an intermittent spray, 8 sprays of 250 ml at 10 °C at 20 min intervals,
during the first 3 h of chilling. The second consisted of 2 sprays, one at 2 h
and the second at 10h post-mortem. These treatments were compared to a
conventional two-stage process, with air at 10°C, 1 m s
-1
for the first 10h,
followed by air at 0 °C, 1 m s
-1
for 14h.
Both treatments significantly reduced weight loss after chilling and this
advantage was retained during 4 further days of storage (Table 6.21).
There were small (<1 h) but significant reductions in the cooling rates of
spray-chilled loins and legs owing to sustained evaporative cooling of the
wetted surfaces. No effects on texture or drip loss and only slight effects on
surface lean and fat colour were found.
No significant differences in bacterial numbers were found between
treatments after chilling and storage. There were small but significant
increases (<1 log cycle) on all diaphragms and on the breasts of double-
sprayed carcasses (Table 6.22).
6.3.3 Immersion chilling
6.3.3.1 Pork
All frozen poultry is initially chilled by being immersed in chilled water or
an ice water mixture.The procedure is very rapid and the birds actually gain
weight during the process. Whole carcasses or even sides of pork are too
big to handle in this way. It is possible, however, to hot joint the pork into
primal cuts, vacuum pack the primals and then chill them by immersion in
Primary chilling of red meat 125
Table 6.21 Mean weight losses and standard deviations
() from conventional and spray-chilled lamb carcasses
Treatment Weight loss (%)
8 h 24 h 5 days
Conventional 1.16
a
(0.25) 2.20
a
(0.24) 3.97
a
(0.55)
Multiple spray -0.01
b
(0.25) 0.86
b
(0.15) 2.97
b
(0.27)
Double spray 0.78
c
(0.21) 1.20
c
(0.28) 3.19
b
(0.42)
Values within columns with different superscripts are significantly
different (P < 0.05).
Source: Brown et al., 1993.
iced water or brine. The vacuum packaging prevents water pick up and
overcomes any possibility of cross contamination, both of which are con-
sidered a problem in the poultry system.
In immersion chilling trials (Brown et al., 1988), pigs were slaughtered,
dressed and split into sides. Sides were then cut into primals (shoulder, leg,
loin and belly), vacuum packed and immersed in a tank of refrigerated agi-
tated brine at 0 °C. The primals were then placed in a chill room operating
at 0°C.
The average temperature of the loin and belly primals was reduced to
7 °C within a 2–3 h period and legs and shoulders in 6h in the immersion
system. Evaporative weight loss was reduced by over 2% in the immersion
chilling system (Table 6.23) and this yield advantage was still maintained
after 14 days further storage.
126 Meat refrigeration
Table 6.22 Mean values and standard deviation () from conventionally and
spray-chilled lamb carcasses
Treatment Site Total viable count (log 10)
Before chilling After storage
Conventional Leg 3.44 (0.44) 3.42 (0.66)
Breast 3.89 (0.67) 4.05 (0.60)
Diaphragm 2.81
ax
(0.35) 3.17
y
(0.41)
Multiple spray Leg 3.80 (0.71) 3.85 (0.48)
Breast 4.05 (0.58) 4.32 (0.55)
Diaphragm 3.11
bx
(0.19) 3.47
y
(0.35)
Double spray Leg 3.45 (0.36) 3.39 (0.26)
Breast 3.91
x
(0.38) 4.32
y
(0.38)
Diaphragm 2.81
ax
(0.26) 3.40
y
(0.52)
Values for each site within columns with different superscripts (a,b) and between rows (x,y)
are significantly different (P < 0.05).
Source: Brown et al., 1993.
Table 6.23 Mean evaporative and drip losses from immersion and
conventionally chilled pork, and work done in shearing cooked samples
Immersion Control Difference
Evaporative loss (%) 0.32 2.40 -2.08
?
Drip in vacuum pack (%) 0.36 0.25 +0.11
Drip in retail packs (%) 1.52 1.52 0.00
Work done (J)
1 day conditioning 0.30 0.25 +0.05*
14 days conditioning 0.23 0.20 +0.03
Difference significant at
?
P < 0.001, * P < 0.05.
Source: Brown et al., 1988.
6.3.4 Ice bank chilling
6.3.4.1 Pork
Another possible way of reducing weight loss is to increase the humidity of
the air in the chilling system. In the early stages of chilling when the surface
of the carcass is still much warmer than the air in the room, humidity has
little effect. However, during the later stages of cooling and in subsequent
storage its effect can be substantial.
Ice bank refrigeration systems produce high humidity air at a steady tem-
perature close to 0 °C and have proven advantages in storage of fruit and
vegetables. Such systems use refrigeration coils or plates to cool tanks of
water and then build up ‘banks’ of ice.The chilled water is then used to cool
and humidify air, by direct contact, which is in turn used to cool the product.
The ice bank is energy and cost effective because it uses smaller compres-
sors operating at full power and hence high efficiency. It can also be run
overnight on off-peak electricity to build up the bank of ice for use the next
day. This bank can then be used to overcome the high heat loads that are
initially produced when the hot pigs are loaded into the chill room.
In studies (Gigiel and Badran, 1988) during the first 24 h, the carcasses
in the ice bank room lost 0.4% less weight than those chilled in the con-
ventional chill room (Table 6.24). Over the subsequent 2 days in storage,
the pigs in the ice bank room lost little additional weight, while those in the
conventional chill room lost 0.9%. The use of a prechilling stage before the
ice bank did not further reduce weight loss.
In all treatments the majority of the heat was removed from the car-
casses in less than 12 h. After this time the deep leg temperature was less
than 7 °C and the surface of the leg, the highest surface temperature on the
carcass, was below 5 °C. The average temperature of the carcass would be
approximately 4 °C.
Primary chilling of red meat 127
Table 6.24 Times for deep leg temperatures to fall to
7 °C and average weight losses for the ice bank and
control regimes
Treatment Time to 7 °C Percentage weight
(h) loss at post-mortem
24 h 48 h 72 h
1 11.90
ac
1.94
a
2.02
a
1.92
a
2 9.60
b
2.37
b
2.79
b
3.31
b
3 11.70
ab
1.80
a
1.94
a
1.88
a
4 10.40
ab
1.83
a
2.00
a
2.03
ac
5 11.30
ab
2.07
c
2.20
a
2.17
c
Means within columns with different superscripts are significantly
different (P < 0.05).
Source: Gigiel and Badran, 1988.
The only problem encountered experimentally was that of surface tex-
ture, experienced butchers subjectively judging that the ice bank chilled
carcasses were less firm and more slippery than those chilled convention-
ally. In commercial use, ice banks would also require more space than con-
ventional chilling systems. To reduce 250 pig carcasses of 63kg average
weight from 35 to 7 °C would require 5000 kg (5.4 m
3
) of ice.
6.3.5 Combined systems
A number of investigations have been carried out into the use of different
chilling systems in combination.
6.3.5.1 Pork
Neel et al. (1987) investigated the combination of electrical stimulation fol-
lowed by a short initial spray chill using iced water, then immersion chill-
ing. Pork carcasses, average market weight 98.6kg, were either stimulated
(550 V for 30 s, 2 s on 1 s off) or unstimulated. Sides were then chilled for
20 min using an ice water shower system (30l s
-1
at 2°C) for 20min. Loin
primals were then cut from the sides, vacuum packed and chilled for 2.5 h
in brine at -2.2 °C. Controls were chilled for 24h in air at 2°C before cutting
and immersion chilling for 30 min.
After immersion chilling, temperatures were very similar under the two
systems, ranging from 0 to 5 °C in the spray chilled and 2–6 °C in the control
loins. After storage for 21 days at 0°C drip loss was highest, 1.27% from the
stimulated and 1.09% from the unstimulated, spray chilled meat compared
with 0.71 and 0.78% from the conventionally chilled. Pork from all treat-
ments was rated tender by the taste panel and ratings for overall desirabil-
ity did not differ significantly. All the pork was evaluated as acceptable or
highly acceptable so the authors concluded that the accelerated system
could considerably reduce processing time, space and energy while main-
taining quality.
Long and Tarrant (1990) looked at the effect of combining a preslaugh-
ter shower with post-slaughter rapid chilling on temperature, weight losses
and eating quality of pork meat. Showering caused a reduction in deep loin
temperature at 40 min post-mortem and there was a strong indication of
reduced drip from winter showering. The treatments had no effect on
cooking loss or toughness of longissimus dorsi muscle.
The effect of immersing pork sides for 3 min in liquid nitrogen before
conventional chilling was investigated by Jones et al. (1991).The main effect
of the treatment was to reduce evaporative loss by 1.6% over the first 24 h
of chilling. No significant differences were found in any of the other para-
meters measured, which included colour, texture, drip and bacterial sur-
vival. However, laboratory trials with strips of chilled pork showed that
immersion in liquid nitrogen was effective in reducing inoculated popula-
tions of aerobic spoilage pseudomonads.
128 Meat refrigeration
6.3.6 Protective coatings
6.3.6.1 Lamb
Popov and Vostrikova (1985) and Lazarus et al. (1976) have investigated
the use of a protective coating, applied prior to chilling, to reduce weight
loss. In the method, an edible animal fat and starch emulsion or a calcium
alginate film (Flavor–Tex) was sprayed over the entire carcass straight after
dressing. Savings in weight loss of up to 1.20% for the Flavor–Tex treated
and 1.14% for the fat emulsion treated after 24h post-mortem were found.
Wrapping the carcass in a plastic film (low moisture and high oxygen trans-
fer) resulted in savings in weight loss of up to 1.5% after 24h chilling when
compared with non-wrapped controls. The results of these studies showed
that evaporative weight loss can be reduced by the use of either protective
coating. However, considerations of the carcass cooling rate and microbial
growth favoured the edible coating since it cools slightly quicker and pro-
duces lower microbial counts than the plastic wrap.
6.3.7 Hot boning
6.3.7.1 Beef
An obvious way of overcoming many of the problems associated with
carcass chilling is to bone the carcass whilst hot and cool the resulting
primal joints (Cuthbertson, 1977, Taylor et al., 1980/81; Williams, 1978).
However, the hot wet cut surfaces are easily contaminated and subject to
a very high rate of evaporative weight loss unless wrapped. The potential
hygiene problem has resulted in the Australian Department of Primary
Industry specifying maximum cooling times (see Table 6.25) (Herbert and
Smith, 1980).
The cooling times are difficult, if not impossible, to meet using conven-
tional refrigeration systems and many consider them unreasonably strict.
However, the importance of good hygiene and fast cooling of hot-boned
meat is generally accepted. The majority of hot-boned beef is chilled inside
580 ￥ 380 ￥ 150 mm fibreboard cartons containing ca. 25 kg of primal cuts.
Primary chilling of red meat 129
Table 6.25 Maximum cooling times to 8 °C for hot-
boned meat with different initial temperatures
Initial meat temperature (°C) Time to 8 °C (h)
40 4.0
35 5.0
30 6.0
25 7.5
20 9.5
Source: Herbert and Smith, 1980.
The most severe conditions that can be used in practice without partial
freezing (air -1°C,5ms
-1
), will achieve complete chilling from 40 to 2°C in
24 h. This time is more than doubled to 54h using still air at the same tem-
perature. The poor conductivity of the fibreboard, the layer of entrapped
air, and the thickness of the meat, prevent even plate cooling systems (which
produce high surface heat transfer coefficients) from achieving cooling
times below 17 h.
These cooling times are too long to make conveyerised chilling systems
economic unless very high throughputs are required; consequently, most
hot-boned meat is chilled in batch systems. Careful design and operation of
these systems are required to achieve acceptable air flows over the top and
bottom faces of the cartons. Air gaps of at least 5 cm between layers of
cartons are required which considerably reduces packing density in the
chiller and necessitates double handling if the meat is to be stored and
transported on pallets. The batch systems also suffer from the same peak
load problems as carcass chillers.
Bell et al. (1996) studied hot-boning of bull beef and chilling in either
vacuum or CO
2
packs. Cooling times to 7 °C were ca. 13 and 20h, respec-
tively. The authors stated that the process could produce high quality beef
for catering use with a storage life of 70 days at ca. 0°C.
Attempts have been made to compensate for the poor conductivity of
the packaging material by introducing a quantity of liquid nitrogen into
the carton before the lid is applied (Herbert, personal communication).
This was partially successful in reducing the peak load on the refrigeration
system and increasing the cooling rate, but substantial surface freezing
occurred and nitrogen spillage produced a safety hazard in the cutting
rooms. Greater success has been achieved by packing the meat in cartons
and then adding 20% by weight of carbon dioxide pellets (Gigiel, 1985).
Meat with an initial temperature of 30°C cooled to an average tempera-
ture of 0 °C after 22 h without any further refrigeration being required. Con-
sequently, the cartons could be assembled into pallets and/or transported
directly after carbon dioxide addition. Very little refrigeration would sub-
sequently be required to protect the meat from environmental heat gains.
After 7 days storage the yield from the hot-boned carbon dioxide chilled
meat was 3% more than that from conventionally chilled cold-boned con-
trols. In this particular application the saving in weight loss more than offset
the extra cost of solid carbon dioxide over conventional refrigeration.
Further work showed that increased drip caused by partial freezing of a
thin surface layer in contact with the solid carbon dioxide was balanced by
reduced drip from the rapidly chilled but not frozen inner regions (Gigiel
et al., 1985).
Computer predictions indicated that the CSIRO cooling requirements
could be attained in primals chilled in 158mm deep aluminium moulds in
a plate freezer operating with plate temperatures of -35°C (Visser, 1986).
Cooling times of 5 h from 40 to 2°C would allow for a continuous opera-
130 Meat refrigeration
tion. An automatic plate freezer cooling and subsequently freezing 800
cartons of hot-boned beef per day is now in operation in Australia (Anon,
1986). The system as designed would not be suitable for chilled meat
production. Computer predictions show that if surface freezing is to be
avoided, meat thickness would have to be reduced to below 8 cm before the
CSIRO requirements could be achieved in a plate or immersion chilling
system (James, 1988).
6.3.7.2 Pork
A whole range of technologies exists to overcome some, if not all, of the
problems already identified, dependent to some extent upon the degree
of further processing applied. As early as the 1950s, several progressive
sausage manufacturers in the USA, who were also engaged in pig slaugh-
tering, deboned hot (less than 1 h post-mortem) sow carcasses (Kauffman,
1987). The resulting prerigor muscles were treated with salt or sometimes
polyphosphates and this procedure improved the water-holding capacity for
the production of frankfurters. Today, the majority of sows and some boars,
15% of the total pork production, are hotboned and nearly all the muscu-
lature transformed immediately into sausages. This is the most extreme
example of accelerated processing currently in commercial operation, from
pig to sausage in less than 2h. The ATP present in prerigor pork acts as a
natural glue in the production of restructured products and with the trend
towards additive-free food, such processing prerigor bears reexamination.
The rate of diffusion of salt through muscle becomes faster as muscle
temperature rises. Also, the still intact arterial system of the pig immedi-
ately after slaughter provides a good distribution network for curing brine.
Systems have been developed to hot cure bacon by arterially pumping cold
brine into the carcass prerigor. This has the added advantage of partially
cooling the meat, before immersion chilling in a refrigerated brine.
Neel et al. (1987) investigated a system where loins were removed 30min
post-mortem, vacuum packed, held in a water bath at 11°C for 5h then
brine chilled. Drip loss after storage for 21 days at 0 °C was less (0.55%)
than the control and other rapidly chilled treatments. Other sensory para-
meters were similar.
Warm processing where loins were removed from carcasses either 1, 3
or 5 h post-stunning was investigated by Frye et al. in 1985. Three rapid
cooling treatments: immersion in brine at -23°C; CO
2
chilling at -94°C or
packing in CO
2
at -68 °C, were used in the trials. These produced loin tem-
peratures of -2 °C after 1.5–2 h of chilling with no significant difference
between treatments. The crust frozen loins were then tempered and
mechanically portioned. Pork chilled at 1 h post-stunning resulted in high
shear force values and short sarcomere length. For a delay time of 3 h or
more there were no major differences in muscle colour, pH, sarcomere
lengths, drip or taste panel determinations between treatments and a con-
ventionally (0–2 °C chiller) chilled control.
Primary chilling of red meat 131
Warm boning as practised in Denmark is another technology that allows
same day processing and distribution (Hermansen, 1987). Immediately after
dressing, chilling in air at -25 to -30 °C for ca. 80 min is commenced. This
brings the surface temperature down to about -2°C. It is therefore neces-
sary to equilibrate the carcass for one or two hours before cutting and
boning take place. The total chilling loss is about 0.6%. After boning the
meat is either vacuum packed for storage and ageing, wrapped, boxed and
frozen, or cured and tumbled. Not all the heat is extracted during the short
initial blast chilling operation and further cooling is required after cutting.
Van Laack and Smulders (1989) showed that there were no differences in
the microbial and sensory qualities of the ‘warm’ processed pork compared
with cold boned controls. Overall yield was 0.8% higher than that from the
controls.
6.4 Conclusions
1 The factors that control the cooling of a side of meat are the rates at
which heat can be conducted from the innermost tissues to the surface
and from the surface to the circulating air in the chill room. The former
is rate controlling because of the very poor conductivity and consider-
able thickness of the beef hindquarter, although this fact is still not
appreciated by many of those engaged in refrigeration design. Attempts
by contractors to meet continuing commercial pressures for increased
rates of cooling are therefore confined to changing the parameters that
affect surface heat transfer, i.e. temperature, air velocity and humidity.
2 The optimisation of a carcass chilling system will depend upon the
market being supplied. If eating quality is of prime importance, then
cold shortening has to be avoided. For beef and lamb this will be
achieved by specifying a minimum air temperature of 10°C for the first
10 h of chilling or by the application of electrical stimulation. A high air
velocity during this stage will increase the rate of chilling and reduce
the drip loss on cutting.
3 If cost is of prime importance then the minimum weight loss and fastest
throughputs are required. This necessitates low air temperatures, high
air velocities and high relative humidities. Even under these conditions,
it is difficult if not impossible to attain a temperature of 7°C in a
true 24 h cycle with beef and alternative chilling methods should be
considered.
6.5 References
allen d m, hunt m c, luchiari filho a, danler r j and goll s j (1987), Effects of
spray chilling and carcass spacing on beef carcass cooler shrink and grade factors,
J Animal Sci, 64 165–170.
132 Meat refrigeration
anon (1975), Chilling after slaughter, MRI/MLC Technical bulletin no. 4.
anon (1985), Quick chill carcass cooler, Meat Industry (October).
anon (1986), Plate freezer trials, Meat Producer and Exporter, 40 1, 4.
bailey c and cox r p (1976), The chilling of beef carcasses, Proc Inst Refrigeration,
72, session 1975–1976, 76–90.
bell r g, penney n, gilbert k v, moorhead s m and scott s m (1996), The chilled
storage life and retail display performance of vacuum and carbon dioxide packed
hot deboned beef striploins, Meat Sci, 42(4) 371–386.
bowater f j (2001), Rapid chilling plant compared to conventional systems, in Rapid
Cooling of Food, Meeting of IIR Commission C2, Bristol (UK).
bowling r a, dutson t r, smith g c and savell j w (1987), Effects of Cryogenic chill-
ing on beef carcass grade, shrinkage and palatability characteristics, Meat Sci, 21
67–72.
brown t and james s j (1992), Process design data for pork chilling, Internat J
Refrigeration, 15(5) 281–289.
brown t, gigiel a j, swain m v l and higgins j a (1988), Immersion chilling of hot
cut, vacuum packed pork primals, Meat Sci, 22 173–188.
brown t, chourouzidis k n and gigiel a j (1993), Spray chilling of lamb carcasses,
Meat Sci, 34 311–325.
collett p and gigiel a j (1986), Energy usage and weight loss in beef and pork chill-
ing, Recent Advances and Developments in the Refrigeration of Meat by Chilling,
Meeting of IIR Commission C2, Bristol (UK) 171–177.
cooper t j r (1972), The design of carcass chill rooms for the bacon industry, in
Cutting CL, Meat Chilling: Why and How? Meat Research Institute Symposium
No. 2 17.1–17.12.
cox r p and bailey c (1978), Product loads for beef carcass chilling, Proc Inst
Refrigeration, 74, session 1977–1978, 19–28.
crystal b b (1978), Electrical stimulation, refrigeration and subsequent meat
quality, Proceedings of the 24th European Meeting of Meat Research Workers,
E7.1.
cuthbertson a (1977), Hot boning of beef carcasses, Inst Meat Bull, 74 19.
davey c l and garnett k j (1980), Rapid freezing, frozen storage and the tender-
ness of lamb, Meat Sci, 4 319–322.
davey c l and gilbert k v (1973), The effects of carcass posture on cold, heat and
thaw shortening in lamb, J Food Technol, 8 445–451.
dransfield e and lockyer d k (1985), Cold shortening toughness in excised pork
M. Longissimus dorsi. Meat Sci, 13 19–32.
drumm b m, joseph r l and mckenna b m (1992a), Line chilling of beef 1: the pre-
diction of temperature, J Food Eng, 16 251–265.
drumm b m, mckenna b m and joseph r l (1992b), Line chilling of beef 2: the
effect on carcass temperature, weight loss and toughness, J Food Eng, 15 285–312.
earle r l and fleming a k (1967), Cooling and freezing of lamb and mutton. 1.
Cooling and freezing rates in legs, Food Technol, 21 79–84.
frye c b, calkins c r and mandigo r w (1985), Rapid chilling and mechanical por-
tioning as a fresh pork processing system, J Food Sci, 150 1560–1563.
gerosimov n a and malevany b n (1968), Air-radiation system of beef chilling,
Controlled atmosphere cold rooms. Storage of quick frozen products, Meeting
of IIR Commission V, Avignon (France), Annexe 1968–1 Bulletin IIR, 57–63.
gerosimov n a and rumyanstev u d (1972), Heat exchange at radiation –
convective chilling of meat, Khalo-tech, 11 31–34.
gigiel a j (1984), Energy consumption and weight loss in pig chilling, Proceedings
of the 30th Meeting of European Meat Research Workers, Bristol, 2.8, 63–64.
gigiel a j (1985), Chilling hot boned meat with solid carbon dioxide, Internat J
Refrigeration, 8(2) 91–96.
Primary chilling of red meat 133
gigiel a j and badran r j (1988), Chilling and storage of pig carcasses using high
humidity air as produced by an ice bank cooler, Internat J Refrigeration, 11
100–104.
gigiel a j and collett p (1990), Energy consumption, rate of cooling and
weight loss in beef chilling in UK slaughter houses, Internat J Food Eng, 10
255–273.
gigiel a j and creed p g (1987), Effect of air speed, temperature and carcass weight
on the cooling rates and weight loss of goat carcasses, Internat J Refrigeration, 10
305–306.
gigiel a j and james s j (1984), Electrical stimulation and ultra-rapid chilling of pork,
Meat Sci, 11 1–12.
gigiel a j and peck g b (1984), Thousands can be saved in chilling, Meat Industry,
57(8) 30.
gigiel a j, swain m v l and james s j (1985), The effects of chilling hot boned meat
with solid carbon dioxide, J Food Technol, 20 615–622.
gigiel a j, butler f and hudson w r (1989a), Alternative methods of pig chilling.
Meat Sci, 26 67–83.
gigiel a j, collett p and james s j (1989b), Fast and slow beef chilling in a com-
mercial chiller and the effect of operational factors on weight loss, Internat J
Refrigeration, 12 338–349.
greer g g, jones s d m, dilts b d and robertson w m (1990), Effect of spray-
chilling on the quality, bacteriology and case life of aged carcasses and vacuum
packaged beef, Canadian Inst Food Sci Technol J, 23(1) 82–86.
hamby p l, savell j w, acuff g r, vanderzant c and cross h r (1987), Spray-
chilling and carcass decontamination systems using lactic and acetic acid, Meat
Sci, 21 1–14.
heitter e f (1975), Chlor-chill, Proceedings Meat Industry Research Conference,
AMIF, Arlington, VA, 31–32.
herbert l s and smith m g (1980), Hot-boning of meat – refrigeration requirements
to meet microbiological demands, Food Res Quart, Proceedings Strathleven
Conference, Sydney.
hermansen p (1987),‘Warm’ boning of pigs including problems of interfactory trans-
port of chilled meat, in Accelerated Processing of Meat, Elsevier, 127–130.
james s j, unpublished.
james s j (1988), Efficient systems for rapid cooling of carcasses and hot-boned meat,
in Ramila A et al., Accelerated Processing of Meat, Elsevier Applied Science,
49–56.
james s j and bailey c (1990), Chilling of beef carcasses, in Chilled Foods – The State
of the Art, Elsevier Science, 159–181.
james s j, gigiel a j and hudson w r (1983), The ultra rapid chilling of pork, Meat
Sci, 8 63–78.
jeremiah l e and jones s d m (1989), The effects of spray chilling and vacuum pack-
aged storage on purge losses and retail properties of pork, J Food Protection, 52(7)
473–476.
johnson r d, hunt m c, allen d m, kastner c l, danler r j and shrock c c (1988),
Moisture uptake during washing and spray chilling of Holstein and beef-type
steer carcasses, J Animal Sci, 66 2180–2184.
jones s d m and robertson w m (1988), The effects of spray-chilling on the shrink-
age and quality of beef, Meat Sci, 24 177–188.
jones s d m, greer g g, jeremiah l e, murray a c and robertson w m (1991),
Cryogenic chilling of pork carcasses: effects on muscle quality, bacterial popu-
lations and palatability, Meat Sci, 29 1–16.
kadim i t, purchas r w, davies a s, rae a l and barton r a (1993), Meat quality and
134 Meat refrigeration
muscle fibre type characteristics of Southdown rams from high and low backfat
selection lines, Meat Sci, 33 97–109.
kauffman r g (1987), Developments in the United States on accelerated process-
ing: an overview, in Ramila A et al., Accelerated Processing of Meat, Elsevier
Applied Science, 131–143.
kempster a j, cuthbertson a and smith r j (1981), A national survey of the weight
loss in pig carcasses between slaughter and 24 h post mortem, Meat Sci, 5 383–387.
kerens g (1981), Incorrect chilling and freezing practice can be expensive, CSIR
Report ME 1728, Pretoria, SA.
kerens g (1983), Accelerated chilling of beef carcasses, FRIGAIR ’83 Symposium,
CSIR, Pretoria.
kerens g and visser c j (1978), Environmental requirements during beef carcass
chilling, CSIR Report ME 1597, Pretoria, SA.
lang o (1972), The chilling of meat in Germany, in Cutting CL, Meat Chilling: Why
and How? Meat Research Institute Symposium No. 2, 34.1–34.16.
lazarus c r, west r l, oblinger j l and palmer a z (1976), Evaluation of a calcium
alginate coating and a protective plastic wrapping for the control of carcass
shrinkage, J Food Sci, 41 639–641.
lee l m, hawrysh z j, jeremiah l e and hardin r t (1990), Shrouding, spray-chilling
and vacuum-packaged ageing effects on processing and eating quality attributes
of beef, J Food Sci, 55(5) 1270–1273.
long v p and tarrant p v (1990), The effect of pre-slaughter showering and
post-slaughter rapid chilling on meat quality in intact pork sides, Meat Sci, 27
181–195.
lovett d a, herbert l s and radford r d (1976), Chilling of meat, experimental
investigations of weight loss, Towards an Ideal Refrigerated Food Chain, Meeting
of IIR Commissions C2, D1, D2, D3 & E1, Melbourne (Australia),Annexe 1976–1
Bulletin IIR, 307–314.
malton r and james s j (1983), Drip loss from wrapped meat on retail display, Meat
Industry (May) 39–41.
marsh b b and leet n g (1966), Meat tenderness 3, J Food Sci, 31 450–460.
meat research corporation (1995), Measurement of surface temperatures of chilled
carcasses and sides, Meat Technology Update, 95/6, Australian Meat Technology
Meat Research Newsletter.
Mirinz (1985), Bulletin no. 11.
Mirinz (1986/87), Annual report, p.12.
moller a j and vestergaard t (1987), Effect of delay time before chilling on tough-
ness in pork with high or low initial pH, Meat Sci, 19 27–37.
neel s w, reagan j o and mabry j w (1987), Effects of rapid chilling and accelerated
processing on the physical and sensory characteristics of fresh pork loins, J Animal
Sci, 64 765–773.
popov v p and vostrikova n p (1985), Industrial scale experimental application of
edible coating to carcasses and halves before cooling, Kholodilhaya Tekhnika, 10
4748.
rhodes d n (1972), The influence of rate of chilling on texture, in Cutting CL, Meat
Chilling: Why and How? Meat Research Institute Symposium No. 2, 4.1–4.6.
sheffer a p and rutov d g (1970), Reduction of meat weight losses during cooling,
freezing and storage, Weight Losses in Foodstuffs, Meeting of IIR Commissions
II, IV, V & VII, Leningrad (USSR), Annexe 1970–3 Bulletin IIR, 143–150.
sheridan j j (1990), The ultra-rapid chilling of lamb carcasses, Meat Sci, 31–50.
smith g c and carpenter z l (1973), Post-mortem shrinkage of lamb carcasses,
J Animal Sci, 36(5) 862–867.
stiffler d m, savell j w, griffin d b, gawlik m f, johnson d d, smith g c and
Primary chilling of red meat 135
vanderzant c (1985), Methods of chilling and packaging of beef, pork and lamb
variety meats for transoceanic shipment: physical and sensory characteristics,
J Food Protection, 48(9) 754–764.
swain m v l and james s j (1988), Process design data for lamb, mutton and goat
chilling, Meat Chilling, IFR-BL Subject Day, 23 Febuary 1988.
taylor a a, crystal b b and rhodes d n (1972), Toughness in lamb induced by rapid
chilling, J Food Technol, 7 251–258.
taylor a a, shaw b g and macdougall d b (1980/81) Hot boning beef with and
without electrical stimulation, Meat Sci, 5 109–123.
union international consultants (1984), A study of the practical and economic
considerations associated with high velocity and low-temperature air streams for
chilling of beef, Proceedings of the 30th European Meeting Meat Research
Workers, Bristol, 2.1.
vanderzant c, hanna m o, ehlers j g, savell j w, griffin d b, johnson d d, smith
g c and stiffler d m (1985), Methods of chilling and packaging of beef, pork and
lamb variety meats for transoceanic shipment: microbiological characteristics,
J Food Protection, 48(9) 765–769.
van laack r l j m and smulders f j m (1989), Quality of ‘semi-hot’ and cold boned,
vacuum-packaged fresh pork as affected by delayed or immediate chilling, J Food
Protection, 52(9) 650–654.
visser k (1986), Automatic plate freezing of hot boned meats – an alternative to
post slaughter chilling? Recent Advances and Developments in the Refrigeration
of Meat by Chilling, Meeting of IIR Commission C2, Bristol (UK), 279–284.
watt d b and herring h k (1974), Rapid chilling of beef carcasses utilising ammonia
and cryogenic systems: Effect on shrink and tenderness, J Animal Sci, 38(5)
928–934.
wernburg n e (1972), Quick chilling procedures in Scandinavian countries, in
Cutting CL, Meat Chilling: Why and How? Meat Research Institute Symposium
No. 2, 33.1–33.5.
williams s c (1978), Hot boning, Food Technology in Australia, 30 495–497.
136 Meat refrigeration
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