7
Flour Quality
Introduction Table 7.1 shows typical proportions of flour streams
(expressed as percentages of the wheat) from a
well-equipped and well-adjusted mill in the U.K.
yield of the individual flour streams is also shown.
Flour streams with the lowest ash yield (e.g.
group 1 in Table 7.1) may be described as ‘patent’
flour. Those from the end of the milling process
In the milling of cereals by the gradual reduc-
machine in the break, scratch and reduction
systems of the normal mill-flow. The stock fed
to each grinding stage is distinctive in composition
- in terms of proportions of endosperm, embryo
grain from which the endosperm is derived -
and each machine flour is correspondingly distinc-
tive in respect of baking quality, colour and
granularity, contents of fibre and nutrients, and
the amount of ash it yields upon incineration.
By far the most abundant flour consumed in
the industrialized world is derived from wheat;
because of this, and the unique versatility of
wheaten flour, the majority of this chapter is
ti’n system (see Ch’ 6), flour is produced by every
making flours of fairly low ash yield. The ash
and bran contained in it, and the region of the
with high ash yield are called ~l~~-~~~d~’ in the
TABLE 7.1
Typical Proportions and Ash Yields of Flour Streams
Proportions Ash yield
(% of feed (%, d.m.)
Flour streams
Group 1: High Grade
to I Bk)
A 12 .O-2 1.0 0.35-0.38
B 14.0-17.0 0.35-0.38
C 7.0-10 0.38-0.47
3540 0.35-0.40
devoted to it. Flours from other cereals are
however given some consideration.
In the U.K. today there are no recognized
Total group 1
Group 2: Middle Grade
2.5-7.5 0.39-0.70 D
standards for flour grades: each miller makes his E
1.7-2.1 0.45-0.89
grades according to customer’s requirements, and G
1.3-3.0 0.75-1.47
I Bk 1.5-2.5 0.50-0.72
II Bk
quality for any particular grade. I11 Bk
0.0-1.5 0.70-1.00
I11 Bk bran finisher flour 0.0-2.5 0.70-1.00
X (Scratch) 0.0-0.7 0.70-0.90
I Bk Coarse Midds 3.0-6.0 0.50-0.82
Flour grades I1 Bk Coarse Midds 1.5-3.5 0.70-0.84
1.5-3.0 0.53-0.69
exercises his skill in maintaining regularity of
Total Group 2 25-30 0.70-0.80
If the flour streams from all the machines in
Group 3: Low grade
the break, scratch and reduction systems are B2 1.2-2.5 0.40-0.45
the resulting flour is known as ‘straight-run H 0.6-1.2 0.60-1.53
0.5-0.7 0.88-2.25
2.04.0 1.00-2.00
and blending particular flour streams, frequently IV Bk finisher flour 0.0-1.0 1.50-2.00
0.0-1.0 1.00-2.50
8-10 1.80-2.3
blended together in their rational proportions, F 0.7-1.2 0.58-1.35
J
Iv Bk
v Bk
grade’. Other grades are produced by selecting
on the basis of their ash yield or grade colour
(measures of their non-endosperm tissue content).
Total Group 3
170
FLOUR QUALITY 171
replaced chlorine in 1922 as an improving and
bleaching agent for breadmaking flour because it
was much more effective. Its use was discontinued
in the U.S.A. in 1949 and in the U.K. from the
end of 1955, after it had been shown by Mellanby
(1946) that flour treated with Agene in large doses
might cause canine hysteria (although Agene-
treated flour has never been shown to be harmful
to human health). Nitrogen trichloride reacts
with the amino acid methionine, present in wheat
protein, to form a toxic derivative, methionine
sulphoximine (Bentley et al., 1950).
Chlorine dioxide
Chlorine dioxide (C102), known as ‘Dyox’, is
now the most widely used improving and bleaching
agent in the U.K., the U.S.A., Australia and
Canada. It was first used for these purposes in
1949 in the U.S.A. and in the U.K. in 1955. The
gas is produced by passing chlorine gas through
an aqueous solution of sodium chlorite. Dyox gas
contains a maximum of 4% C102. The chlorine
dioxide gas is released by passing air through the
solution, and is applied to breadmaking flour at
a rate of 12-24 mg/kg (it is permitted in the U.K.
up to 30 mg/kg). Chlorine dioxide treatment of
flour destroys the tocopherols (cf. Ch. 14). The
use of chlorine dioxide is also permitted in Japan.
Benzoyl peroxide
(C6H5C0)202 or Bz02 is a solid bleaching
agent which was first used in 1921. It is supplied
as a mixture with inert, inorganic fillers such as
CaHP04, Ca3(P04)2, sodium aluminium sulphate
or chalk. Novadelox, a proprietary mixture, con-
tains up to 32% of benzoyl peroxide but 16% is
the usual proportion. The dosage rate, normally
45-50 mg/kg, is restricted to 50 mg/kg in the
U.K. by the Bread and Flour Regulations 1984.
The bleaching action occurs within about 48 h.
This bleacher has the advantage over gaseous
agents that only a simple feeder is required, and
storage of chemicals presents no hazard; the fact
that it has no improving action is advantageous
in the bleaching of patent flours. The treated flour
contains traces of benzoic acid, but objection has
U.K. or ‘clear’ flour in the U.S.A. Clear flour is
used industrially in the U.S.A. for the manufac-
ture of alcohol, gluten, starch and adhesives (see
Ch. 15).
Treatments of wheat flour
Bleaching
Flour contains a yellowish pigment, of which
about 95% consists of xanthophyll or its esters,
and has no nutritional significance. Bleaching of
the natural pigment of wheat endosperm by
oxidation occurs rapidly when flour is exposed to
the atmosphere, more slowly when flour is stored
in bulk, and can be accelerated by chemical
treatment. The principal agents used, or formerly
used, for bleaching flour are nitrogen peroxide,
chlorine, chlorine dioxide, nitrogen trichloride,
benzoyl peroxide and acetone peroxide.
Nitrogen peroxide (NO,)
NO2 produced by a chemical reaction or by
the electric arc process was widely used as a
bleaching agent in the early twentieth century.
Its use has been discontinued except in the U.S.A
and Australia, where it is still legally permitted.
Chlorine
The use of chlorine gas (C12) for treatment of
cake flour (except wholemeal) is permitted in the
U.K. to a maximum of 2500 mg/kg. The chlorine
modifies the properties of the starch for high-
ratio cake flour (cf p. 178). For cake flours the
usual level of treatment is 1000-1800 mg/kg. The
Bread and Flour Regulations 1984 do not permit
its use in bread flour in the U.K. The use of
chlorine is not permitted in most European
countries, but it is allowed in flour for all purposes
in the U.S.A., Canada, Australia, New Zealand
(to 1500 mg/kg) and South Africa (to 2500mg/kg).
Nitrogen trichloride
This gas (NC13), known as ‘Agene’, was patented
as a flour bleach by J. C. Baker in 1921, and
172 TECHNOLOGY OF CEREALS
not been raised. Bz02 is also used in New South flours (those nearer the tail end of the break and
Wales, Queensland, the U. S.A, Canada, the reduction systems) in general requiring more
Netherlands, New Zealand (up to 40 mg/kg, for treatment than the patent flours (cf. p. 170). It
pastry flour only) and Japan (up to 300 mg/kg). is therefore customary to group the machine
flours according to quality into three or four
streams for treatment. A possible grouping is
indicated in Table 7.1 Each group would be given
Acetone peroxide
Acetone peroxide is a dry powder bleaching appropriate bleacher treatment: e.g. the lowest
and improving agent, marketed as ‘Keetox’, a 20% of flour might receive treatment at ten times
blend of acetone peroxides with a diluent such as the rate for the best quality 50%. The final grades
dicalcium phosphate or starch. The concentration are then made up by blending two or more of the
in terms of H202 equivalent per 100 g of additive groups in desirable proportions.
plus carrier is 3-10 for maturing and bleaching,
or 0.75 for use in doughmaking. Its use has been
permitted in the U.S.A. since 1961, and also in
Canada, but it is not, as yet, permitted in the
with benzoyl peroxide. The usual dosage rate is
446 mg/kg on flour basis. Significant dates in the
history of flour bleaching are summarized in
Table 7.2. Moisture content
Flours for various purposes
Wheat flour is used for making food products
U.K. It is used either alone or in combination
of widely varying moisture content (see Table 7.3).
TABLE 7.3
Flour-based Products and their Moisture Contents
Type of product Range Mean Moisture
(Yo) (”/.I level
Flour blending for bleaching treatment soup 78-80
85 High
13-67 45 Medium
3540 38 Medium
characteristics, the optimum level of bleaching Cakes 5-30 17 Medium
Because the various flour streams differ in their
Puddings
Bread
treatment varies correspondingly, the lower grade Pastry 7 Low
Biscuits (cookies, crackers) 1-6 5 Low
Data extracted from McCance and Widdowson (1967).
The proportions in which the various ingredients
of baked products are present in the recipe,
relative to flour (100 parts), are shown in Table
7.4. Biscuit dough is stiff to permit rolling and
flattening; bread dough is a plastic mass that can
be moulded and shaped; wafer batter is a liquid
suspension that will flow through a pipe.
For comparison with products listed in Table
7.4, a typical wholemeal wheat extruded snack
formulation would contain the following amounts
of ingredients, in relation to 100 g white flour: 7 g
soya protein, l4 g wheat bran, ’ *4 g Oil, Oe4 g
emulsifier, 23 g water, 7 g sugar, 2 g salt, 2 g
dicalcium phosphate, 3.6 g milk powder (Guy,
1993).
The flour content of various flour-containing
products, as purchased or as consumed, is shown
in Table 7.5.
TABLE 7.2
Significant Dates in the History of Flour Bleaching
1901 Andrews patents flour treatment with NO2 (chemical
process)
1903 Alsop patents flour treatment with NOZ (electrical
treatment)
1909 NO2 in use
1911 Keswick Convention - unmarked flour to be
1921 Benzoyl peroxide first used
1921 J. C. Baker patents NC13 as flour bleacher
1922 NC13 replaces Cl as bleacher for breadmaking flour
1923 Committee appointed to inquire into use of
1924 Committee’s activities extended to chemical
1927 Committee reported that bleaching and improving
1949 NC13 use discontinued in the U.S.A.
1949 C102 first used in the U.S.A.
1955 NC13 use discontinued in the U.K.
1955 C102 first used in the U.K.
1961 Acetone peroxide permitted in the U.S.A. (not in the
unbleached
preservatives and colouring matter in food
substances for flour treatment
agents were in use, and that C1, NCI3 and Bz02 were
not among those least open to objection
U.K.)
FLOUR QUALITY 173
TABLE 7.4
Proportions of Constituents in Recipes for Baked Products§ (Relative to Flour: 100 Parts)
Constituents
Type of product Whole Raising Milk
Water Fat Salt egg agent powder Sugar
Yeasted products (Yeast)
Bread, CBP* 61 0.7 1.8 1.8
Bread, LFPt 57 0.7 1.8 1.1
Cream crackers 32 12.5 1.0 0.1-2.0
Short 25 50 2.0
Pie 31 43 2.0
Steak and kidney pudding 30-36 50 0.7
Puff 40-50 50-70 0.7
Choux 125 50 150
Hard sweet 20 17 0.7 1.1* 2.6 22
Soft 10 32 0.1 0.5$ 2.0 30
Plain 50 40 35 3.5* 40
Pastry
Biscuits (whey)
Cake
High ratio 70 65 2.0 60 5.0* 8 120
Sponge 1.0 170 100
Wafer batter 150 3 0.2 0.3$
* Chorleywood Bread Process.
t Long Fermentation Processes.
$ Mixtures of sodium and ammonium carbonate or bicarbonate.
5 Source: FMBRA.
TABLE 7.5
Flour Content of Flour-Based Foods, as Purchased or
Consumed*
moisture contents (at least 7% and not more than
15.5%, respectively), fat acidity, particle size
(98% through a 212 pm sieve) and protocol
for ash determination. Optional ingredients and
approved additives are listed.
(%) (%) ptflour In the U.K., flour for human consumption
should conform with the nutritional requirements
- ‘12 90 set out in the Bread and Flour Regulations 1984
semi-sweet 67-82 74 135 (cf. P. 293).
ginger nut 43-57 49 205 For each purpose, flour with particular proper-
60-80
65 155 ties is required: these are secured, in the first
Bread
Short pastry
Buns, scones, teacakes 3657 45 220 place, by choice of an appropriate wheat grist in
Cakes, pastries, choc. wafer 23-40 33 300 terms of strong and weak wheats. The average
uo 25 4oo composition of wheat grists used for milling flour
Biscuits (chocolate)
Puddings
for various purposes in the U.K. is shown in
flour milled in the U.K. in 1990/91, 63% was
at m.c. of final product.
used for bread, 15% for biscuits, 6% for house-
The Codex Alimentarius Commission of the hold use, 2% for cakes, 2% for starch manufacture
United Nations Food and Agriculture Organiza- and 12% for ‘other products’.
tion issued standard 152 on flour for human ‘Other’ food products made with wheat flour
consumption in 1985. It defines acceptable sources include pastry, meat pies, sausages, sausage rolls,
as Triticum aestivum L. bread wheat, and T. rusks, pet foods, baby foods, invalid foods,
compactum club wheat, the required protein and chapatties, buns, scones, teacakes, pizzas, soups
Parts of
F1our ‘Ontent product
Food product Range Mean per 100
Crispbread
Biscuit
53-72 70 145
846 30 330
* Source: FMBU. Flour wt at natural m.c. Product Wt
Table 4.8. Table 4.8 also shows that, of the total
174 TECHNOLOGY
(Ch. 13), premixes, liquorice, batter (for fish
frying), chocolate and sugar confectionery , cereal
convenience foods, snack foods, breakfast cereals,
puddings, gravy powder, blancmange and brewing
adjunct. Specific requirements for flours for various
purposes are outlined below.
Bread flour
The predominance of wheat flour for making
aerated bread is due to the properties of its protein
which, when the flour is mixed with water, forms
an elastic substance called gluten (cf. Chs 3 and
8). This property is found to a slight extent in
rye but not in other cereals.
The property of producing a loaf of relatively
large volume, with regular, finely vesiculated
crumb structure, is possessed by flours milled
from wheats described as 'strong' (cf. Chs 4 and
8). Protein strength is an inherent characteristic,
but the amount of protein present can be influenced
by the conditions under which wheats are grown.
Protein content is also an important determinant
of bread quality, there being a positive correlation
between loaf specific volume (ml/g) and the
percentage of protein present.
Typical characteristics of Chorleywood Bread
Process (CBP) flour, Bakers' flour (as used in
the bulk fermentation process), and rollermilled
wholemeal in the U .K. are shown in Table 7.6.
Maturing and improving agents
The breadmaking quality of freshly milled
flour tends to improve during storage for a period
of 1-2 months. The improvement occurs more
TABLE 7.6
Typical U.K. Bread Flour Analysis 1992
Redox improvers
The action of improvers is believed to be an
oxidation of the cysteine sulphydryl or thiol
( -8H) groups present in wheat gluten. As a result,
these thiol groups are no longer available for
participation in exchange reactions with disulphide
( -8-8- ) bonds -a reaction which is considered to
release the stresses in dough -and consequently
the dough tightens, i.e. the extensibility is reduced.
Alternatively, it has been suggested that the
oxidation of -8H groups may lead to the formation
Bakers' WholemealCBP
14.6%
11.0%
2.1
329
lSFU
30FU
60.2%
14.5%
12.1%
2.2
334
22FU
34FU
62.0%
14.6%
14.7%
Moisture
Protein
Grade colour
Falling number
alpha-Amylase*
Starch damage
Water absorption
330
21FU
70.2%
* Farrand units, (includes fungal enzyme).
Source: FMBRA.
OF CEREALS
rapidly if the flour is exposed to the action of the
air. During such aerated storage, fat acidity
increases at first, owing to lipolytic activity, and
later decreases, by lipoxidase action; products of
the oxidation of fatty acids appear; the proportion
of linoleic and linolenic acids in the lipids falls;
and disulphide bonds ( -S-S- ) decrease in number .
The change in baking quality , known as matura-
tion, or 'ageing', can be accelerated by chemical
'improvers', which modify the physical properties
of gluten during fermentation in a way that results
in bread of better quality being obtained. Matured
flour differs from freshly milled flour in that it
has better handling properties, increased tolerance
in the dough to varied conditions of fermentation
and in producing loaves of larger volume and
more finely textured crumb.
Improving agents permitted in the U .K. Bread
and Flour Regulations 1984 (SI1984, No.1304), as
amended by the Potassium Bromate (Prohibition
as a Flour Improver) Regulations 1990 (SI 1990,
No.399) are chlorine, (for cake flour only; not
wholemeal), cysteine hydrochloride (920) (all
flour except wholemeal), chlorine dioxide (all
flour except wholemeal), L-ascorbic acid (vitamin
C) (all flour except wholemeal; all bread), and
azodicarbonamide (all flour except wholemeal).
Besides their improving effect, these substances
give a whitened appearance to the loaf because
of their beneficial effect on the texture of the
crumb. Improving agents do not increase the
carbon dioxide production in a fermented dough,
but they improve gas retention (because the
dough is made more elastic) and this results in
increased loaf volume (cf. Ch. 8).
FLOUR QUALITY 175
of new -S-S- bonds which would have the effect the total Br content of the bread to about 18
of increasing dough rigidity (cf. Ch. 3). mg/kg.
Potassium bromate (KBr03) has never been Use of potassium bromate is permitted to 75
allowed in many European countries; it was mg/kg in the U.S.A.; to 50 mg/kg in Canada,
specifically excluded from the list of permitted Sweden; to 40 mg/kg in the Soviet Union; and in
additives in the U.K. by the Potassium Bromate Eire to about 18 mg/kg. KBr03 is not allowed in
(Prohibition as a Flour Improver) Regulations the Netherlands or Australia. The greatest need for
1990 giving rise to considerable initial difficulties bromate occurs in continuous-mix baking, no-time
in the baking industry. The changes in the use doughs, frozen doughs, and overnight sponges,
of oxidizing improvers, consequent upon the as used in Cuba and other LatdAmerican coun-
deletion of potassium bromate, are considered in tries. The typical level of addition in these types
Ch. 8 (p. 201). Its use has also been voluntarily of baking approaches the 75 mg/kg maximum.
discontinued in Japan and it is now little used in (Ranum, 1992).
New Zealand. Hazards associated with potassium L-Ascorbic acid (vitamin C), E300, was first
bromate include the fact that, as a strong oxidizing used as a bread improver by Jgrgensen in 1935.
agent, it can cause fire or explosions. It is also It is now used for this purpose in the U.K., most
toxic and there is strong evidence for its carcino- European countries and elsewhere, particularly
genicity . At normal levels of addition however, in mechanical development processes of bread-
it is not considered to persist at a significant level, making, such as the Chorleywood Breadmaking
into the baked product, when used at permitted Process. The volume increase resulting from use
levels. of ascorbic acid is generally less than that obtained
Potassium bromate remains in use in the U.S.A. with equivalent weight of potassium bromate,
although an agreement exists between Government and it is more costly. The improving effect of
and users to reduce usage to a minimum. Although ascorbic acid is mediated by enzymes present in
permitted in Canada, its use has declined in recent the flour. The functional form is the oxidized
years in that country (Ranum, 1992). It has been form dehydroascorbic acid (DHA), which is
used commercially as a bread improver since highly effective but cannot be used directly as it
1923. The rate of treatment is 10-45 mg/kg on is unstable. Ascorbic acid is oxidized to DHA
flour weight. The substance acts as an oxidizing through catalytic action of ascorbic acid oxidase.
agent after the flour has been made into a dough; Injection of oxygen during mixing hastens the
it increases the elasticity and reduces the extens- oxidation, making ascorbic acid more effective
ibility of the gluten. Treatment with bromate has (Chamberlain and Collins, 1977). The oxidation
a similar action to that of ageing or maturing the to DHA is improved if the head space of the
flour, and enables large bakeries to use a constant mixing machine contains an oxygen-enhanced
fermentation period. atmosphere, e.g. a 5050 mixture of oxygen
Potassium bromate is added to flour after being and air, equivalent to a mixture of 60% oxygen
suitably diluted with an inert filler such as calcium plus 40% nitrogen (Ch. 8). Under these circum-
carbonate or calcium sulphate. Proprietary brands stances, ascorbic acid alone is as effective an
of improver contain 6, 10,25 or 90% of potassium oxidizing agent as is a combination of ascorbic
bromate. The 6% brand is added at the rate of acid and potassium bromate used when the dough
0.022%. Higher levels of potassium bromate are is mixed under partial vacuum. An enzyme ‘DHA
used in chemical dough development processes reductase’ is required for oxidation of sulphydryl
(cf. Ch. 8). (-SH) compounds by DHA.
Since untreated flour contains 1-8 mg/kg of Ascorbic acid strengthens the gluten; gas reten-
bromine (Br), the bread made with untreated tion is thus improved and loaf volume augmented.
flour contains 0.7-5.6 mg/kg of natural Br. Flour Ascorbic acid does not hasten proving. The
treatment with 45 mg/kg of bromate leaves a maximum permitted levels (1989) are 50 mg/kg
residue of 15 mg/kg of Br in the loaf, increasing in Belgium and Luxembourg, 100 mg/kg in the
176 TECHNOLOGY OF CEREALS
Netherlands, 200 mg/kg in Canada, Denmark, other than wholemeal; higher levels (up to
Italy, Spain, the U.S.A. and the U.K., 300 mg/kg 300 mg/kg) are permitted in certain biscuit flours.
in France. No maximum level is specified in Use of L-cysteine is permitted in Denmark (up
Australia, Greece, Portugal, Germany since to 25 mg/kg), Germany (up to 30 mg/kg), Belgium
ascorbic acid is reckoned to be quite safe, although (up to 50 mg/kg), Australia, New Zealand and
it is under scrutiny by the COT. Use of ascorbic the Netherlands (up to 75 mg/kg), Canada (up to
acid is also permitted in Japan, New Zealand and 90 mg/kg) and Sweden (up to 100 mg/kg).
Sweden. L-Cysteine is not mentioned as a permitted addi-
Azodicarbonamide (1,l ’azobisformamide; tive in France, Greece, Italy, Luxembourg,
NH2CONNCONH2; ‘ADA’) is a flour maturing Portugal, Spain or the U.S.A.
agent, marketed as ‘Maturox’, or ‘Genitron’, or Cysteine accelerates reactions within and
as ‘ADA 20%’ (‘AK20’). ‘Maturox’ contains between molecules in the dough which lead to an
either 10% or 20% of ADA; ‘Genitron’ contains improvement in its viscoelastic and gas-holding
20% or 50% of ADA, dispersed in an excipient, properties. These reactions normally take place
generally calcium sulphate and magnesium car- slowly during bulk fermentation but with the
bonate. The particle size of ADA is generally 3- addition of cysteine the bulk fermentation period
5 pm. It was first used in the U.S.A. in 1962 can be eliminated. Cysteine, which is a rapid-
(maximum permitted level 45 mg/kg on flour acting reducing agent, is used in the ADD in
weight). When mixed into doughs it oxidizes the conjunction with slow-acting oxidizing agents,
sulphydryl (-SH) groups and exerts an improving such as ascorbic acid and potassium bromate
action. Oxidation is rapid and almost complete (where permitted) or azodicarbonamide, which
in doughs mixed for 2.5 min. Short mixing times complete the ‘activation’ commenced by the
are thus appropriate. The residue left in the flour cysteine. The dough-softening action of cysteine
is biurea. Flour treated with ADA is said to reduces the work input required for the production
produce drier, more cohesive dough than that of fully developed dough.
treated with chlorine dioxide, to show superiority
in mixing properties, and to tolerate higher water
Blending for improver treatment
absorption. An average treatment rate is 5 mg/kg
(on flour weight) in bulk fermentation and low- The principles applied to bleaching flours of
speed mixing methods of baking, and 20-25 different grades also apply to improver treatment
mg/kg (on flour weight) in the high-speed mixing (cf. Table 7.1).
Chorleywood Bread Process (CBP). The agent
Emulsifiers and stabilizers
does not bleach, but the bread made from treated
flour appears whiter because of its finer cell
structure. The use of ADA has been permitted, to ‘Emulsifiers’ and ‘stabilizers’ are any substances
a maximum level of 45 mg/kg, in the U.K. since capable of aiding formation of (emulsifiers) or
1972. Its usage is also permitted in Canada, New maintaining (stabilizers) the uniform dispersion
Zealand and the U.S.A., but not in Australia or of two or more immiscible substances. Flours,
in EC countries other than the U.K. (1989). sold as such, are not allowed to contain emulsifiers
L-Cysteine is a naturally occurring amino acid, but the following are permitted by the Bread and
is used in the Activated Dough Development Flour Regulations (1984) to be included in bread:
process (ADD) (cf. Ch. 8), in which it functions E 322 lecithins; E460 a-cellulose (permitted only
as a reducing agent. The addition of L-cysteine in bread for which a slimming claim is made);
(in the form of L-cysteine hydrochloride or E466 carboxymethyl cellulose, sodium salt (per-
L-cysteine hydrochloride monohydrate) to bread mitted only in bread for which a slimming claim
doughs, for this purpose, is permitted by the is made); E471 mono- and di-glycerides of fatty
Bread and Flour Regulations 1984 in the U.K. acids; E472(b) lactic acid esters of mono- and
to a maximum level of 75 mg/kg in bread flours di-glycerides of fatty acids; E472(c) citric acid
FLOUR QUALITY 177
esters of mono- and di-glycerides of fatty acids; coarse a flour produces incomplete sheets of
E472(e) mono- and di-acetyl tartaric acid esters of unsatisfactory wafers.
mono- and di-glycerides of fatty acids; E481 Gluten development in wafer batters must be
sodium stearoyl-2-lactylate (cf. Ch. 8); E482 avoided, so flours which have a low tendency to
calcium stearoyl-2-lactylate; E483 stearyl tartrate; give an aggregated gluten under low shear rates
E481 and E482 are subject to a maximum level in aqueous flour batters are required. Hence low
of 5000 mg/kg. protein flours with weak extensible glutens are
normally specified (cf. p. 186).
Cracker doughs have fully developed gluten
networks and protein quality is important in
Biscuit (cookie, cracker) flour
Biscuit flours for short and semi-sweet biscuits dough processing. Cracker flours with medium
are typically produced from grists containing protein contents (9.5-10.5%) made mainly from
mainly soft wheats, with some hard wheats hard wheats are commonly used. Matzos are
included to increase the rate of production in the water biscuits made from unbleached, untreated
mill. However, hard wheat flours produce thinner flour and water only.
biscuits than those of soft wheats so it is important
Emulsifiers
to use a narrow range of levels of hard wheat in
the flour. The level specified will depend on the
manufacturer’s preference since the biscuit plant Emulsifiers are used in biscuits, either as
will have to produce biscuits of particular sizes processing aids or as partial replacements for fat.
and weights to suit the packing plant. Very low levels (e.g. 0.1% on fat basis) of sodium
There is no developed gluten network in short stearoyl-2-lactylate (E48 1) in sheeted biscuit
biscuit doughs, hence neither the level nor quality doughs produce a smooth, non-sticky surface
of protein is significant in production. However, which aids dough-piece cutting. Lecithin (E322)
consistency of quality is critically important in is commonly used in wafer batters to aid release of
modern, high-speed production plants. Flours the baked wafer from the wafer baking machinery.
would normally be specified to have, say, a range Emulsifiers which can replace a substantial propor-
of 1% protein within the typical range for flours tion of fat in biscuits without serious deterioration
(8-1 0%). in product quality are sodium stearoyl-2-lactylate
Semi-sweet biscuits have a developed gluten and the diacetyltartaric acid esters of mono-
network which is modified during processing, glycerides of fatty acids E472e. Lecithin can be
and for these biscuits low protein flours (typically used to replace a low level of fat in biscuits.
8.5-9.5%) with weak, extensible glutens are used.
Flours for confectionery products
At present, sulphur dioxide (SO*, usually obtained
from sodium metabisulphite added at the mixer)
Cake flours
is used to increase the extensibility and decrease
the elasticity of the doughs. This aids control of
the dough sheet and hence biscuit thickness. EC Flour in cakes should allow an aerated structure
proposals include permission of SO2 in fine to be retained after the cake has been built up.
bakery wares, up to 50 mg/kg in the final product. The stability of the final cake depends largely
Nevertheless wheat breeders are seeking to develop upon the presence of uniformly swollen starch
varieties which perform well without its use. granules; hence, the granules should be undamaged
For wafers, low protein flour milled from weak during milling, free from adherent protein, and
wheat is suitable. Particle size is an important unattacked by amylolytic enzymes. These charac-
characteristic; ideally about 55% should be below teristics are found in flour milled from a soft,
40 pm, 35% between 40 and 90 pm, and not more low-protein wheat of low alpha-amylase activity.
than 10% coarser than 90 pm. Too fine a flour Typical parameter values for cake flour milled
produces light, tender, fragile wafers, while too in the U.K. would be as follows: Untreated cake
178 TECHNOLOGY OF CEREALS
flour: 8.5-9.5% protein and aminimum of particles at a level of about 0.5-1 .O% of batter weight,
exceeding 90 pm in size. Fine particle size is more whisking times can be greatly reduced, all-in
important than low protein content for cake mixing methods can be used and liquid egg can
quality, giving finer, more even crumb than that be replaced with dried egg.
given by a coarser flour. Foam-promoting emulsifiers such as GMS,
Strong cake flour (for fruit cakes): 12% poly-glycerol esters, propylene-glycol esters (E477)
protein, 20-25 FU starch damage, 0.18% chlorine or blends of these, used at about 1% of batter
treatment. weight, allow a reduction in the fat content of a
cake or even substitution of the fat by a smaller
quantity of vegetable oil.
Although anti-staling effects of emulsifiers in
High-ratio flour
In the late 1920s it was discovered, in the cakes are not as clearly defined as in bread,
U.S.A., that cake flour which had been bleached sucrose esters (E473), sodium stearoyl lactylate
with chlorine gas to improve its colour permitted (E481) and poly-glycerol esters (E475) offer some
production of cakes from formulae containing possibilities as a means of minimizing the effects
levels of sugar and liquid each of which is in of staling.
excess of flour weight. Such flour for use in
high sugar/flour ratio and high liquid/flour ratio
Flour for cake premixes
formulae is known as ‘high-ratio flour’. It should
also have fine, uniform granularity and low protein Some cake premixes sold in Britain contain, in
content. The chlorination treatment, generally powder form, all the ingredients required for a
0.1-0.15% by weight, besides allowing addition cake, viz. flour, fat, sugar, baking powder, milk
of larger proportions of liquid and sugar, reduces powder, eggs, flavouring and colour, and need only
elasticity of the gluten and lowers the pH to 4.6- the addition of water before baking. However,
5.1. some cake premixes, particularly those sold in the
Heat treatment of the grain or of the semolina U.S.A., omit the eggs and/or the milk, because
from which the flour is milled has been found to lighter cakes of larger volume can be made by the
be an effective substitute for the chlorine treat- use of fresh eggs instead of dried ingredients.
ment of high-ratio cake flour (BP nos 1444173 The type of flour must be suitable for the
(FMBRA) and 1499 986 (J. Lyons)) (cf. p.171) particular product, flours of high-ratio type gener-
and cake flours may be similarly treated. ally being used. The fat must have the correct
Typical characteristics of high-ratio flour milled plasticity and adequate stability to resist oxida-
in the U.K. would be 768.4% protein, 2&25 FU tion. The addition of certain antioxidants to fat,
starch damage, granularity such that 70% of the to improve stability, is allowed in Britain, the
particles were below 32 pm in size and a minimum U.S.A. , and elsewhere. Those allowed in Britain
of particles exceeding 90 pm in size. High-ratio under the Antioxidants in Food Regulations 1978
flour is particularly suitable for sponge-type goods. (S.1 1978 No. 105, as amended) for addition to
anhydrous oils and fats, and certain dairy products
other than butter, for use as ingredients are
propyl, octyl or dodecyl gallates up to 100 mg/kg,
Emulsifiers in cakes
In cake making, emulsifiers such as glycerol or butylated hydroxyanisole (BHA) and/or
monostearate (GMS) and mono- and di-glycerides butylated hydroxytoluene (BHT) up to 200
of fatty acids (E471) are used in soft fats at levels mg/kg (calculated on the fat). Those allowed in
of up to 10% to produce high-ratio shortenings. the U.S.A. (with permitted levels based on fat or
Certain emulsifiers such as GMS, polyglycerol oil content) are: resin guaiac (0.1%), tocopherols
esters and lactic acid esters of mono-glycerides (0.03%), lecithin (0.01%)) citric acid (0.01%),
(E472b) possess remarkable foam-promoting pyrogallate (0.01%), propylgallate (0.02%) and
properties so that when added to sponge batters BHA and/or BHT (0.02%).
FLOUR QUALITY 179
wheat has been denatured it is not suitable for
breadmaking. The flour may, for many purposes,
be regarded as impure starch, and is often used
to replace starch in certain types of adhesives,
and as a filler for meat products.
The bacteriological status of flour for soups is
important and requires not > 125 total thermo-
philic spores per 10 g, not >50 flat sour spores per
10 g, not >5 sulphide spoilage organisms per 10 g,
thermophilic anaerobic spores in not >3 tubes out
of 6.
Quellmehl
Quellmehl or heat-treated starch, is defined as
maize flour or wheat flour of which the starch
has undergone hydrothermic (vzz. steam) treat-
ment resulting in pregelatinization of the starch
thereby increasing its swelling capacity by at least
50%.
Flour for sausage rusk
A low protein flour milled from weak wheat,
such as U.K.-grown Riband, or a low protein air-
classified fraction is required. Desirable charac-
teristics are low maltose figure (not > 1.4 by Blish
and Sandstedt method), low alpha-amylase activity
(high Falling Number) and high absorbency.
Batter flour
A low protein flour milled from a grist com-
prising 90% weak British wheat plus 10% strong
wheat is suitable. Alpha-amylase activity should
be low. Too high a viscosity in the batter caused
by excessive starch damage is to be avoided, and
therefore the proportion of hard wheat in the grist
should be restricted.
Household flour
Household flour is used for making puddings,
cakes, pastry, etc. In the U.K. it is milled from a
grist consisting predominantly of weak wheats of
low protein, such as British or Western European,
with admixture of up to 20% of strong wheat to
promote flowability and good mixing. Exclusion
In preparing the premixes, the dry ingredients
are measured out by automatic measures and
conveyed, often pneumatically, to a mixing bin,
mixed, and then entoleted (cf. p. 111) to ensure
freedom from insect infestation. The fat is then
added, and the mixture packaged. If fruit is
included in the formula, it is generally contained
in a separate cellophane-wrapped package enclosed
in the carton.
Flour for fermented goods
For buns, etc. a breadmaking flour is required.
Fermentation time is short; the fat and the sugar
in the formula bring about shortening of the
gluten.
Flour for pastry
A weak, medium strength flour is needed for
the production of sweet and savoury short pastes.
Flour strength for puff pastry will vary according
to the processing methods, with rapid processing
methods requiring weaker flours than those used
in traditional methods of production. In general,
flours for puff pastry should have low resistance
to deformation (e.g. low Brabender resistance
values) but reasonable extensibility.
Flour from steamed wheat
Flour milled from steamed wheat ('stabilized'
flour, in which enzymes have been inactivated)
is produced for use in manufacture of soups (Ch.
7), gravies, crumpets, liquorice and as a thickening
agent. For these purposes, the flour should form
a thick paste when it is heated with water, and
the paste should retain its consistency for some
time when heated at 9Oo-95"C. The alpha-amylase
activity of normal (non-steam-treated) flour is
usually high enough to degrade swollen starch
granules during the cooking process, resulting in
loss of water-binding capacity and formation of
thin pastes of low apparent viscosity. The greater
water-absorbing capacity of the flour from steamed
wheat could also make it a suitable ingredient for
canned pet-foods.
As the gluten in the flour from steam-treated
180 TECHNOLOGY OF CEREALS
of sprouted wheat from the grist is important (cf. acid pyrophosphate (SAPP) diluted with starch
Ch. 4), as high alpha-amylase activity leads to the and used in the ratio of 2: 1 with sodium hydrogen
production of dextrins and gummy substances carbonate at a rate of 4.7% on flour weight.
during cooking, and to sticky and unattractive
lnstantized or agglomerated flour
baked goods.
This a form of free-running flour, readily
Self-raising flour
dispersible in water, made by ‘clustering’ flour
This is a household flour to which raising particles in an ‘Instantizer’. Uses include the
agents have been added. Choice of sound wheat making of sauces and gravies and for thickening
is important because evolution of gas during and general culinary purposes. In the instantizing
baking is rapid and the dough must be sufficiently process, the flour as normally milled is damped
distensible, and yet strong enough to retain the with steam, tumbled in a warm air stream to cause
gas. The moisture content of the flour should not the particles to agglomerate, then dried, sieved,
exceed 13.5% in order to avoid premature reaction cooled and packed. The U.S. standard for agglom-
of the aerating chemicals and consequent loss of erated flour requires all the flour to pass through
aerating power. a sieve of 840 pm aperture width and not more
Distension of the dough is caused by carbon than 20% to pass through a sieve of 70 pm
dioxide which is evolved by the reaction between aperture width. Free-flowing flour is also produced
the raising agents (U.S.: leavening agents), one by air classification (cf. Ch. 6).
alkaline and one acidic, in the presence of water.
The usual agents used for domestic self-raising
Flour for export
flour in the U.K. are 500, sodium hydrogen
carbonate (‘bicarbonate’) (NaHC03) and acid Besides the specific requirements according to
calcium phosphate, (ACP, E341 calcium tetra- the purpose for which the flour is to be used,
hydrogen diorthophosphate) (CaH,(PO&), and flour for export must have low moisture content
their use was described by J. C. Walker in BP to prevent development of mould, taint or infesta-
No 2973 in 1865. The usual rate of usage is 1.16% tion during its transportation. As a safeguard, the
bicarbonate plus 1.61% of 80% grade ACP flour should be entoleted. In addition, export
on flour weight. A slight excess of the acidic flour must conform to any special requirements
component is desirable, as excess of bicarbonate of the importing country, e.g. regarding the
gives rise to an unpleasant odour and a brownish presence or absence of nutrients and improvers,
yellow discolouration. The Bread and Flour for which the regulations of most other countries
Regulations 1984 permit the following raising differ from those of the U.K. (cf. Ch. 14).
agents in the U.K.: 500, sodium hydrogen In January 1988 the (U.S.) Food and Drug
carbonate, E341 calcium tetrahydrogen diortho- Administration (FDA) announced guidelines for
phosphate (monocalcium phosphate (ACP)), E450 contamination levels at which flour is seizable.
disodium dihydrogen diphosphate (sodium acid These levels are 75 insect fragments or more per
pyrophosphate (SAPP)), 541 acidic sodium 50 g flour and an average of one rodent hair or
aluminium phosphate (SAP), 570 D-glucono-1,5- more per 50 g flour.
lactone and E336 mono potassium+( +)-tartrate
(cream of tartar).
Flours from cereals other than wheat
ACP used at a rate of 1.61% on flour weight
adds about 250 mg Ca per 100 g flour; hence, Besides wheat, all other cereals yield flour when
self-raising flour does not require chalk to be subjected to milling processes as outlined in Ch.
added to it (cf. Ch. 14). Phosphate-starch mixtures 6. The uses for these flours, both commercially
are known as cream powders, a commonly used and domestically, are many and varied, as the
commercial example of which consists of sodium following summary indicates.
FLOUR QUALITY 181
The former finds uses in the food industry, while
the latter is reported to make a unique beer. The
major food uses for malt products and cereal
syrups are in bread, biscuits, crackers, crisp-
bread, breakfast cereals, infant and invalid foods,
malted food drinks, pickles and sauces, sugar
confectionery and vinegar.
Oat flour
Rye flour
Rye flour of various extraction rates is used
extensively in Eastern Europe for making a range
of breads - both soft breads and crispbreads -
using conventional straight dough or sour dough
processes.
Rye flour is also used as a filler for sauces,
soups and custard powder, and in pancake flour
in the U.S.A., and for making gingerbread in
France. A mixture of 10% of rye flour with 90%
crackers in the U.S.A. The rye flour is said to
expensive than wheat flour. Rye flour can be
fractionated by air-classification; a flour of 8.5%
protein content yielded high and low protein
fractions of 14.4% and 7.3% protein contents
match and plastics industries.
This is made by grinding oatmeal on stones
flour is also obtained as a by-product of groat
and for ready-to-eat breakfast cereals, e.g. shredded
products made by a continuous extrusion cooking
process (Ch. 11) and an extruded gun-puffed
product (Ch. 11).
concentrate by the air-classification (Ch. 6) of oat
flour has been described (Cluskey et al., 1973).
(N x 6.25, d.b.) was obtained which comprised
2-5% of the flour by weight. The compound
granules of oat starch (Ch. 2) tend to disinte-
grate upon fine grinding, releasing the individual
granules, which measure 2-10 pm. Separation of
an almost pure protein fraction would therefore
require the use of an extremely fine Cut size __
less than 2 pm.
Of wheat flour is used for making biscuits and
and sifting OUt the fine material (cf. Ch. 6). Oat
improve the quality Of the products and is less
cutting. Uses for oat flour include infant foods
respective1y* Rye flour is a1so used in the glue,
A process for the separation of a protein
Rye flour can also be used for making gun-
puffed and shredded ready-to-eat breakfast cereals'
An ultra-fme fraction with 85-88% protein content
Triticale flour
The use of triticale flour in breadmaking is
mentioned in Ch. 8, and its use in making
chapattis is referred to in Ch. 13. Other bakery
products made with triticale flour include pancakes
and waffles.
Barle y flour Rice flour
Barley flour is used in the manufacture of flat
bread, for infant foods and for food specialities.
It is also a component of composite flours used
for making yeast-raised bread (cf. Ch. 8).
Pregelatinized barley flour, which has high
absorbent properties, provides a good binder and
thickener. Barley breading is made by combining
pregelatinized barley flour with barley crunch.
Malted barley flour is made from barley malt
(cf. Ch. 9). Malt flour is used as a high diastatic
supplement for bread flours which are low in
natural diastatic activity, as a flavour supplement
in malt loaves, and for various other food products.
Malted barley flour can be air-classified (cf. Ch.
6) to yield protein-rich and protein-poor fractions.
This is used in refrigerated biscuit manufacture
to prevent sticking; in baby foods, as a thickener;
in waffle and pancake mixes, as a water absorbent.
The use of rice flour, in blends with wheat flour,
to make bread of acceptable quality, is mentioned
in Ch. 8, and also its use, as a component of
composite flours, for breadmaking. Rice flour can
also be used for making pasta products.
Maize f,our
This is used to make bread, muffins, dough-
nuts, pancake mixes, infant foods, biscuits, wafers,
breakfast cereals, breadings, and as a filler, binder
and carrier in meat products.
182 TECHNOLOGY OF CEREALS
Dry milled maize flour is not to be confused through collaborative testing, by various standard-
with ‘corn flour’, the term used in the U.K. izing organizations. Most countries have national
for maize starch obtained as a product of wet- Standards Organizations (e.g. British Standards
milling. Institute, BSI), and international standards are
The inclusion of maize flour in composite flour also produced by e.g. the International Association
used for breadmaking, and its use, alone, to make of Cereal Science and Technology (ICC), Inter-
bread of a sort in Latin America, are mentioned national Standards Organization (ISO) and
in Ch. 8. The use of maize flour, in blends with American Association of Cereal Chemists (AACC).
wheat semolina, to make pasta products is men- Tests may be applicable to whole grains or
tioned in Ch. 10 and for making extrusion-cooked derived products, in the case of whole grains it
ready-to-eat breakfast cereals in Ch. 11. may be necessary to grind them to achieve an
Industrial uses for maize flour are noted in appropriate particle size distribution.
Ch. 15. For valid comparisons to be made it is necessary
to observe proper sampling procedures (ICC 130,
AACC 64) and to normalize results of most tests
to a constant moisture basis. Either a dry matter
basis or a 14% moisture basis is usually adopted. As
test procedures become more stringent, protocols
increasingly demand that test samples contain a
consistent dry weight of sample, requiring an
adjustment of the actual mass taken to compen-
sate for moisture variation, rather than subsequent
correction. Moisture content must thus be deter-
mined by an acceptable method, such as deter-
mination of weight-loss when the ground product
is heated at 100°C for 5 h in vacuo or at 130°C
for 1 h (flour) or 1.5 h (ground wheat) at
atmospheric pressure. (ICC lOl/l). These methods
are suitable for moisture contents up to 17%. Oven
methods are primary methods as they deter-
mine directly the required parameter; secondary
propem which varies as a function of the requhed
parameter, and thus require calibration against
a standard. Secondary methods are frequently
more rapid but less accurate than oven methods;
hey include electfical conductivi~ and N~~~ infra-
Sorghum and millet flours
Sorghum flour is used as a component of
composite flour for mhg bread in those corntries
in which sorghum is an indigenous crop (cf. Ch.
8).
The use of flour or wholemeal from sorghum
and SOme of the millets to make porridge, Toti,
chapatti, tortilla and other products is described
in Ch. 13.
Sorghum flour finds industrial uses, e.g. as
core-binder, resins, adhesives, and in oil-well
drilling (cf. Ch. 15).
Composite flours
lished by the Food and Agriculture Organization
in 1964 to find new ways Of using flours Other
than wheat - particularly maize, mi11et and
sorghum - in bakery and pasta products, with
the objective of stimulating local agricultural
The Composite F1our Programme was estab-
methods may also be used, they measure a
production^ and saving foreign exchange, in those
countries heavily dependent on wheat imports
red Reflectance Spectroscopy (NIRS) methods
(IS0 202, covers moisture and protein determina-
(Kent, 1985).
tions). NIRS determinations are based on absorp-
tion of NIR energy at specific wavelengths by OH
bonds in water molecules. The same is true of
protein determinations where the peptide bonds
between amino acids define the critical wave-
lengths. Considerable mathematical processing
of signals and measurements at reference wave-
lengths are necessary to ensure accurate indications
of the required parameters.
Quality control and flour testing
Testing protocols, and acceptable degrees of
reproducibility (agreement between laboratories)
and repeatability (agreement between replicate
determinations by the same operator using the
same equipment), have been established, usually
FLOUR QUALITY 183
Parameters dependent on the nature of
the grains milled
Sedimentation tests
These provide a useful indication of the suit-
ability of a flour (it is more usually performed on
Protein content
a ground wheat) for breadmaking. The Zeleny
Protein content of whole grains, meals and test (Pinkney et al., 1957) (AACC 56-60, ICC
flours may be calculated from nitrogen contents 116) has been adopted in a number of countries
determined by the Kjeldahl method (AACC 46) for protein evaluation. It depends on the superior
in which organic matter is digested with hot swelling and flocculating properties, in a dilute
concentrated sulphuric acid in the presence of a lactic acid solution, of the insoluble proteins of
catalyst. Ammonia, liberated by addition of an wheats with good breadmaking characteristics
excess of alkali to the reaction product, is separ- (Frazier, 1971). In the U.K. a better guide to
ated by distillation and estimated by titration. A breadmaking properties has consistently been
convenient apparatus is the Tecator Kjeltec 1030 obtained using the SDS sedimentation test (Axford
Auto System (IS0 1871). In white wheat flour, et al., 1979) rather than the Zeleny test. The SDS
protein content is estimated by multiplying N2 test has been standardized as BS 4317, part 19,
content by 5.7, and in many references this factor and it has been adopted for evaluation of T. durum
is used for other wheat products and other cereals. quality as ICC 5670 and AACC 15 1. It consists
However FAONlrHO (1973) recommend factors of an initial suspension and shaking of ground
appropriate to individual foodstuffs. Those relating material in water, to which sodium dodecyl
to cereals are given in Table 7.7. sulphate is later added. Following a series of
carefully timed inversions of the cylinder con-
taining the suspension, it is allowed to stand for
20 min after which the height of sediment is read.
The test is performed under controlled temperature
conditions.
TABLE 7.7
Factors Used forConvertingKjeldah1 Nitrogen toprotein Values
Wheat fraction Factor Cereal Factor
Wholemeal flour 5.83 Maize 6.25
Flours, except
wholemeal 5.70 Rice 5.95
Pasta 5.70 Barley, oats, rye 5.83 Enzyme tests
Bran 6.31
One of the most important enzymes influencing
flour quality is alpha-amylase. Its activity may be
For routine estimations of protein (and moisture) determined directly, using the method of Farrand
content NIRS methods are now very reliable for (1964) or McCleary and Sheehan (1987), or
whole grains as well as their derivatives. Deter- indirectly, as a result of its solubilizing effect on
minations are carried out at intake and on-line starch, leading to a reduction in paste viscosity.
during processing, in many cereals plants through- The most widely adopted method uses the Falling
out the world. Number apparatus to detect starch liquefaction
For determining the amount of wheat protein in a heated aqueous suspension of flour or (more
contributing to gluten, the Glutomatic instru- usually) ground grain (ICC Standard Method
ment (Falling Number Co) and method may be 107, AACC 56-81B). As enzyme activity can
used. A dough is prepared from a sample of flour vary dramatically among individual grains it is
or ground wheat, and a solution of sodium essential to grind a large sample of grain (at least
chloride. Wet gluten is isolated by washing this 300 g) in preparing a representative meal, and to
dough with a solution of buffered sodium chloride mix it thoroughly before taking the test sample
and, after removal of excess water, weighed, or (7 g at 15% m/c) from it. Wholemeals also require
dried and weighed according to whether wet or regrinding and thorough mixing, and flours have
dry gluten content is required (ICC 137, AACC to be free of lumps. Following the preparation of
56-81B). a suspension in a special tube, this is introduced
184 TECHNOLOGY OF CEREALS
into the apparatus and the test proceeds auto-
matically. The suspension is heated and stirred
at a programmed rate for 60 sec, after which a
plunger is allowed to fall through it. The Falling foam-type cake tests also appear under
Number is the number of seconds from the start
of heating to the coming to rest of the plunger.
A similar principle underlies stirring tests with
the Rapid Visco-Analyser .
Used on grain or grain products to measure
alpha-amylase, both insments probably also
respond to hydrolysis of other viscous components
such as proteins and ceu-wall components, but the
effects of these are usually comparatively small.
Heat damage test for gluten
The effect of overheating on gluten is measured
directly by a method introduced by Hay and
Every (1990). Described as the glutenin turbidity
test, the procedure measures the loss in solubility
of the fraction of glutenins normally soluble
in acetic acid. Dilute acetic acid extracts are
precipitated by addition of alkaline ethanol and
the precipitate is quantified by spectrophotometric
measurement of turbidity allowing the degree
of damage to be assessed by comparison with
standards. Good correlations have been found
between loss of turbidity and reductions in baking
quality.
Pigmen tation
The yellow colour of durum semolinas is highly
valued. Under ICC 152 the carotenoid pigments
are extracted at room temperature with Water-
saturated butanol for Photometric evaluation of
Optical density Of the Clear filtrate against a
p-carotene standard.
End-use tests
version of the same. Several bread baking tc
appear under AACC 10 and ICC 131, rye flc
is tested by AACC 10-70. Biscuit (cookie) E
10-heading. Pasta semolinas are also subjectec
approved small scale tests (AACC 66-41 and -4
Machinability test
In adopting a test for bread wheats eligible
Intervention Price SUPPOrt, the EC has not St
dardized a breadmaking test but instead '
defined flour Of breadmaking quality as flc
which produces dough which does not 'stick
the blades or the bowl of the mixer in which
dough is mixed, nor to the moulding apparat
Extraneous matter test ('filth test')
The rodent hair and insect fragment COUn,
flour is determined by digesting the flour ~
acid and adding the cooled digest to petrol i
separating funnel. The hair and insect fragme
are trapped at the petroVwater interface, and,
be collected and identified microscopically.
Tests for characteristics dePendent
mainlY on Processing conditions
Ash test BS 4317 Part 10
The ash test (incineration of the material i
furnace at a specified temperature and un
prescribed conditions, and the weighing of
resultant ash) is widely used as a measure
&g refinement because pure starchy endospc
yields relatively little ash, whereas bran, aleurc
and germ yield much more. The ash test can
carried out very precisely, but, as the endospe1
of different wheats vary in mineral content, a gi.
ash value can correspond to different levels
bran content. The test is not suitable for indicat
the content ofnon-stuchy-endosprm compone
in flours to which chalk has been added.
In spite of much research no single test has Yet
been devized which Can reliably predict the
breadmaking properties of an unknown wheat or
flour. Hence for this application, and for many
other applications of cereals, the most reliable
means of evaluating a sample is to subject it to
the intended end-use itself, or to a scaled down
Grade Colour
The Grade Colour test, performed, for exam]
with the Kent-Jones and Martin Colour Grac
FLOUR QUALITY 185
can be used to estimate the degree of contamina- Donelson and Yamazaki (1962) and Barnes (1978)
tion of white flour with bran particles. In the test, rely on assaying reducing sugars (mainly maltose)
the intensity of light in the 530 nm region, produced by the action of alpha-amylase derived
reflected from a standardized flourlwater paste, from malt flour. Another method (Gibson et ai.,
in a glass cell, is compared with that reflected 1992) employs amyloglucosidase to further hydro-
from a paste of a reference flour. The grade colour lyze oligosaccharides to glucose, which is then
was said to be unaffected by variation in content determined by the effect of a derivative on a
of flour pigment (xanthophyll) (cf. p. 171). It has chromogen.
now been demonstrated however, that this is not Damaged starch granules may be recognized
so (Barnes, 1978), thus diminishing the value of microscopically by a red coloration with Congo
the test as a means of quantifying bran content. Red (colour index: 22120) stain (cf. Ch. 6), and
have been described, from their microscopical
Tristim ulus methods appearance, as ‘ghosts’ by Jones (1940). Un-
damaged granules do not stain with Congo Red.
Use of an instrument designed to simulate the
A method of damaged starch determination, in
visual response of the human eye has found favour
which damaged and undamaged granules are
in some applications, as an alternative to the
measured separately taking advantage of their
Grade Colour system. The instrument depends
different staining reactions with a fluorescent dye,
upon complex mathematical transforms to produce
has been developed, using image analysis for
values in three arbitrary spectral ranges, X, Y and
making the measurements.
Z, which cannot be produced by any real lights
(Hunter and Harold, 1987). Users can derive a
Whiteness index to suit their needs, by selecting Particle size analysis
from these values. Like the Grade Colour system
Test sieving by hand or sieve shakers tends to
it responds to factors other than bran content -
be unreproducible on flour, but the Alpine air-
probably particle-size - and it thus has a limited
jet sieve, in which negative pressure below the
usefulness (Evers, 1993).
sieve assists particles through the mesh, and
clears the mesh with reversed air-jets, gives more
reproducible analyses. Sedimentation methods
Damaged starch
The amount of starch that is mechanically depend upon the faster settling rates of larger
damaged influences a flour’s ability to absorb particles, in a non-aqueous solvent; the Andreassen
water. The content of damaged starch in flour is pipette is an example of a simple device using
estimated by methods which measure either the this principle (ICC 127), another is the Simon
digestibility or the extractability of the starch. Sedimentation Funnel. Sedimentation methods
Digestibility-based methods measure the amount are not much used today in flour quality control,
of hydrolysis effected by added amylase enzymes; having been superseded by more reproducible
extractability-based methods measure the amount methods. The Coulter counter is a device which
of amylose present in an aqueous extract by its rapidly measures the volume of thousands of
reaction with iodine in potassium iodide. The individual particles as they pass through an
iodine/amylose complex may be assayed colori- orifice. Each particle is measured by the change
metrically (e.g. McDermott, 1980), ampero- in electrical resistance that it causes by displacing
metrically or potentiometrically (e.g. Chopin SD 4 its own volume of the electrolytic solution (non-
method). Only the damaged granules are suscept- aqueous in the case of flour) in which the particles
ible to amylase at temperatures below gelatiniza- are suspended. Reproducibility is very good with
tion temperature and appreciable leaching of this method (Evers, 1982) which is suitable for
amylose occurs only from damaged granules flours and starches but not wholemeals. Laser
under the test conditions. diffraction-based instruments provide a means of
Methods such as those of Farrand (1964), making rapid comparisons among flours. There
186 TECHNOLOGY OF CEREALS
are many instruments of this type available,
some capable of operating on dry samples. The
distributions that they indicate may not agree well
among different instruments or with those of the
other methods described.
Physical tests on doughs and slurries
The physical characteristics of doughs and
slurries are important in relation to the uses
of flours. Pseudo-rheological characteristics are
investigated mainly with the following:
The Brabender Farinograph (D' Appolonia and
Kunerth, 1984) measures and records the resist-
ance of a dough to mixing as it is formed from
flour and water, developed and broken down.
This resistance is called consistency. The maximum
consistency of the dough is adjusted to a fixed
value by altering the quantity of water added.
This quantity, the water absorption (cf Ch. 8),
may be used to determine a complete mixing
curve, the various features of which are a guide
to the strength of the flour (AACC 54-21, ICC
115).
Preston, 1991) (ICC 114, AACC 54-10) records
the resistance of dough to stretching and the
distance the dough stretches before breaking. A
flour-salt-water dough is prepared under standard
conditions in the Brabender Farinograph and
moulded on the Extensograph into a standard
shape. After a fixed period the dough is stretched
and a curve drawn, recording the extensibility of
the dough and its resistance to stretching (see Fig.
7.1). The dough is removed and subjected to a
further two stretches. The Extensograph has
replaced the Extensometer in the Brabender
instrument range but the older instrument is still
widely used for testing biscuit flours.
The Chopin Alveograph (AACC 54-30) uses
air pressure to inflate a bubble of dough until it
bursts; the instrument continuously records the
air pressure and the time that elapses before the
dough breaks.
The Brabender Amylograph (ICC 126 for wheat
and rye flours) continuously measures the resist-
ance to stirring of a 10% suspension of flour in
water while the temperature of the suspension is
raised at a constant rate of l.S"C/min from
20"-95"C and then maintained at 95°C (Shuey and
Tipples, 1980). It is of use in testing flour for
soups, etc., for which purpose the viscosity of
the product after gelatinization is an important
The Brabender Extensograph (Rasper and characteristic (cf. Ch. 6), and for adjusting the
malt addition to flours for breadmaking (cf. p. 62).
The Rapid Visco Analyser (RVA), produced
by Newport Scientific, in Australia, may be
regarded as a derivative of the Amylograph.
weak medium
500
-
e
v)
C
3
.-
L
0
E \ \
\ \ 1-
$
C
d strong
% 500
w
/ 4
$
9
\
cm 5 10 15 20 5 10 15 20
FIG 7.1 Extensometer curves of unyeasted doughs made from flours of different strengths as indicated.
FLOUR QUALITY 187
Measurements of viscosity are made using small 32 kg when packed; the multiwall kraft paper
samples, containing 34 g of starch, in periods bags are stacked, often several tiers high, on pal-
which may be as short as 2 min. Use of disposable leting. The harshness of treatment to be expected
containers and mixer paddles eliminates the need during filling and handling influences the number
for careful washing of the parts between tests. As of plys in the walls of the chosen bags. Using
with the Amylograph, the characteristics of starch single-spout packers approximately 300-350 bagsh
pastes and the effects of enzymes on them can be can be filled. Using multi-spout packers, with up
recorded on charts. They can also be transferred to 8 spouts, 600-800 bags/h are possible.
in digital form, direct to a data-handling computer. The hazards to flour in storage include those
The capacity for measuring the liquefying to wheat in storage, vzz. mould and bacterial
effects of enzymes on viscous pastes enables the attack, and insect infestation (cf. Ch. 6) and
RVA to be used for detecting the products of also oxidative rancidity (cf. Ch. 3) and eventual
sprouted grains in cereal meals. deterioration of baking quality.
True rheological instruments. In recent years Freedom from insect infestation during storage
frustration with instrument-dependent units can be ensured only if the flour is free from insect
obtained with some of the above methods, together life when put into store, and if the store itself is
with the poor reproducibility from one instru- free from infestation. Good housekeeping in the
ment to another of the same type, has led cereal mill and the milling of clean grain should ensure
chemists to turn to true rheological measure- that the milled flour contains no live insects,
ments. Suitable instruments for use with doughs, larvae or eggs, but as a precautionary measure
slurries and gels, derived from flours, include flour is often passed through an entoleter before
the Boklin VOR (viscometric, oscillation and being bagged off, or going to bulk bins. The
relaxation), the Carri Med CSL Rheometer and entoleter (BP No 965267) is a machine consisting
the Rheometrics RDA2. In addition to providing of a rotor rapidly rotating within a fixed housing.
excellent reproducibility, these instruments, which The flour is fed in centrally and is flung with
are also used on many non-food, and many non- considerable impact against the casing. At normal
cereal food materials, allow comparisons to be speeds of operation (2900 rev/min for flour) the
made across a wide range of substances. Although machine effectively destroys all forms of insect
they are expensive, and may never feature life and of mites, including eggs (cf. Ch. 5). The
prominently in routine testing, they will undoubt- insect fragments, however, are not removed from
edly enable the development of tests that can be the flour by the entoleter.
performed on simpler, dedicated instruments The optimum moisture content for the storage
(Faridi and Faubion, 1990). of flour must be interpreted in relation to the
length of storage envisaged, and to the prevailing
ambient temperature and r.h., remembering that
flour will gain or lose moisture to the surrounding
Storage of flour
It has been recommended that, for long periods atmosphere unless packed in hermetically sealed
of conservation, flour should be stored in a closed containers. For use within a few weeks, flour can
atmosphere (Bellenger and Godon, 1972). In be packed at 14% m.c., but at moisture contents
these conditions, flour acidity increases owing higher than 13% mustiness, due to mould growth,
to accumulation of linoleic and linolenic acids, may develop, even if the flour does not become
which are slowly oxidized; reduction of disulphide visibly mouldy. At moisture contents lower than
groups (-S-S-) is slow, and there is little increase 12%, the risk of fat oxidation and development
in sulphydryl groups (-SH); solubility of gluten of rancidity increases. The reactions involved in
protein decreases; as a result, changes in baking oxidative rancidity are catalyzed by heavy metal
strength are only minor. ions, such as Cu*+.
Flour is stored commercially in bags or in bulk The expected shelf life of plain (Le. non-self-
bins. Bags of flour in the U.K. contain 50 or raising) white flour packed in paper bags and
188 TECHNOLOGY OF CEREALS
stored in cool, dry conditions and protected from
infestation is 2-3 years. The rate of increase in
acidity increases with temperature rise and with
fall in flour grade (i.e. as the ash residue increases).
Hence, the shelf-life of brown and wholemeal
flours is shorter than that of white flour.
Stored at 17°C (62"F), the shelf-life of brown
flour of 85% extraction rate and of wholemeal
(100% extraction rate) is closely related to the
moisture content and temperature. Brown flour,
for instance, should keep 9 months at 14% m.c.,
4-6 months at 14.5% m.c., 2-3 months at 15.5%
m.c. For wholemeal stored under the most favour-
able conditions, a shelf life of 3 months may be
expected, or of 12 months if the product has been
entoleted.
Flour blending
Blending of finished flours is widely practised
on the continent of Europe and it is becoming
increasingly popular in the U.K. It can ensure
greater uniformity in a product and it can provide
flexibility in response to requirements for flours
of unusual specification, through the blending of
separately stored flours of various types. Blending
can be performed as a batch process or on a
volumetric basis. The simpler volumetric method
depends upon flours being discharged from two
or more bins into a common conveyor, their
discharge rates being controlled to provide the
respective proportions required. The more accurate
batch method involves the use of weighers to
deposit required weights of products from each
of the selected bins into a batch mixer. An
additional advantage of the batch system is that
improvers can be added at the same time as the
flours are mixed. The mixers used may be of
the ribbon type where the blend is continually
tumbled, or the air mixer type in which the blend
is agitated by air injected into a holding bin.
Bulk storage and delivery of flour
The storage of flour in bulk bins, and delivery
in bulk containers, has advantages over storage
and delivery in bags. Although constructional
costs of bulk storage facilities are high, the
running costs are low because manhandling is
much reduced, and warehouse space is better
utilized.
The capacity of bins for storing flour in bulk
is 70-100 t. Packing pressure inside the bin
increases with bin area, not with bin height; a
bin area of 5.6 m2 is satisfactory. Normally bins
are constructed of concrete or metal. Wooden
bins are liable to become infested. The choice of
construction material is a personal one but steel
is currently most popular as metal bins are
cheaper (unless capacity is over 20,000 tonnes),
they do not crack, they are easily installed and
relocated, and they are immediately usable on
completion of construction (Anon., 1989). The
inner surfaces must be smooth to allow stock to
slide down the walls. Steel bin walls are usually
coated with shellac varnish and lower parts may
be painted with a low-friction polyurethane paint.
Concrete surfaces are ground and coated with
several coats of sodium silicate wash to provide
a seal. The shape of bins is again a matter of
choice. Circular bins are cheaper as lighter gauge
steel may be used, however, there is more space
wasted between cylindrical bins than between
rectangular bins. A problem that can arise, when
flour is discharged from the base of the bin, is
bridging of stock: this can be avoided by good
hopper design and efficient dischargers. Bins may
be filled and emptied pneumatically; fluidizing
dischargers use 0.8-1.1 m3/min of low-pressure
air (20-70 kN/m2) to fluidize the flour, causing
it to behave as a liquid and to flow down a reduced
gradient to the outlet. Mechanical (worm or screw
type), and vibratory dischargers may also be used
to assist discharge of flour from bins. When flour
and air are present in appropriate proportions
there is a risk of dust explosions if a source of
ignition is also present. In all flour conveying and
handling situations, it is essential to avoid sources
of ignition arising. Additional precautions include
the incorporation of explosion relief panels into
bin tops. Similar panels are recommended in the
areas of buildings surrounding the bins.
Flour was first delivered in bulk in the 1950s
and by 1987, 65% of flour delivered in the U.K.
was in bulk (Anon., 1989).
Bulk wagons for transport can be filled at the
FLOUR QUALITY 189
FARRAND, E. A. (1964) Modern bread processes in the
United Kingdom with special reference to a-amylase and
starch damage. Cereal Chem. 41: 98-1 11.
FRAZIER, P. (1971) A Physico-chemical Investigation into the
Mechanism of the Zeleny Test. PhD thesis.
GIBSON, T. s.9 ALQUALLA, H, and MCCLEARY, B. v. (1992)
An improved enzymic method for the measurement of
starch damage in wheat flour. 3. Cereal Sci. 15: 15-27.
GUY, R. (1993) Ingredients. In: The Technology of Extrusion
Cooking. N. FRAME. (Ed.) Blackie, Glasgow.
HAY, R. L. and EVERY, D. (1990) A simple glutenin turbidity
test for the determination of heat damage in gluten.
J. Sci. Food Agric. 53: 261-270.
HOLLAND, B, WELCH, A. A., UNWN, I. D., Buss, D. H.,
PAUL, A. A. and SOUTHGATE, D. A. T. (1991) McCance
and Wddmson’s The Composition of Foods, 5th edn, The
Roy. SOC of Chem. Cambridge.
HUNTER, R. S. and HAROLD, R. W. (1987) The Measurement
ofAppearance. 2nd Edn. John Wiley & Sons, NY. U.S.A.
JONES, C. R. (1940) The production of mechanidy damaged
starch in milling as a governing factor in the diastatic
activity of flour. Cereal Chem. 15: 133-169.
KENT, N. L. (Technical Ed.) (1985) Technical compendium
mill by gravity feed or by blowline, or, most
efficiently, by fluidzed delivery from an outload
bin direct1y above the vehic1e* By this method
flow rates of 250-300 t/h can be achieved. Dis-
charge of the vehicle is assisted by air pressure;
some larger tankers have a fluidizing Pad in the
base of each hopper. Compressors mounted either
On the vehic1e Or at the customer’s premises b1ow
the de1ivery direct to the storage bins at the
bakery.
Mini-bulk containers, holding up to about 2 t,
may be Used in Some mil1S for transport and
delivery of products - mainly bran and germ,
but in some cases flour also.
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190 TECHNOLOGY OF CEREALS
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