12 Chemicals
Biscuit making involves the use of a number of chemicals, the most
generally used of which are salt, leavening agents and fruit acids.
The usage rates of all of these chemicals are small so they are
never handled in bulk. They are delivered and stored in bags, boxes
or sacks.
Most of the chemicals are used as fine crystals or powders. They
tend to become caked and lumpy during storage so the storage
conditions and the length of time they are in store should be
monitored closely. Chemicals may require sieving before use.
12.1 Salt, sodium chloride
Salt is obtained from natural deposits and the sea. It is usually
purified and then vacuum dried to a desired crystal size. It has no
smell and is a white material like sugar. It can be safely checked by
taste to distinguish it from sugar. A flaky, or dendritic, type obtained
from the USA is used to garnish certain savoury crackers.
Salt is used in almost all recipes for its flavour and flavour
enhancing properties. Its most effective concentration is around 1-
1.5% based on the flour weight, but at a level of more than 2.5% the
taste becomes unpleasant.
Because the usage rate is low in doughs the particle size is not
critical as all the salt will soon become dissolved in the dough water.
However, where it is used as a surface dressing the size is important
and it is normal to use a fine particle size. Salt is hygroscopic in
most atmospheric conditions causing it to become damp, non-free
flowing and lumpy. Solutions of salt cause corrosion of iron and
aluminium so it should therefore be stored in airtight containers of
plastic or stainless steel. Unopened bags should be stored in dry
conditions.
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Chemicals 71
12.2 Baking soda, sodium bicarbonate, ‘soda’
This compound is relatively cheap and is obtainable in various
particle size grades, for example, free running grade, refined
standard grade and fine granular. Each of these is suitable for
baking, but coarser grades may not dissolve sufficiently quickly
during the preparation and baking of a dough and will result in dark
brown soda specks on the biscuit surface. This will also be the case if
the soda is lumpy when added to the dough and does not adequately
disperse during mixing.
In the presence of moisture, soda will react with any acidic
materials to liberate carbon dioxide gas. As many biscuit ingredients,
including flour, have an acidic reaction it is often useful to use
sodium bicarbonate as a means of adjusting the acidity of the dough
and thence the taste of the resulting biscuits. If the carbon dioxide
liberated is required as a raising agent it is best to keep the soda away
from the other ingredients as long as possible by, for example in
multistage mixes, adding at the last stage with the flour. In these
circumstances the soda powder must be evenly dispersed through the
mix and if necessary the soda should be screened with a fine sieve
before use to remove any lumps. An excess of sodium bicarbonate
will give biscuits with an alkaline reaction and a yellowish crumb and
surface colouration with an accompanying unpleasant taste (this taste
is known as soda bite).
12.3 Acid salts used as baking powders
Domestic baking powders are balanced mixtures of sodium
bicarbonate and an acid or acid salt. When they become wet or
when the dough is heated they react to liberate a gas, carbon dioxide,
the bubbles of which are the basis of the open structure in a baked
biscuit or cake. In the biscuit industry it is unusual to use blended
baking powders and the soda and acid salt are added separately. Self-
raising flour has baking powder added.
12.4 Acid salts
Several different acid salts can be used in doughs but the most
common are acid calcium phosphate, (ACP) and sodium acid
pyrophosphate, (Puron or SAPP). Both of these are fine white
powders with an acrid acid taste. SAPP is to be preferred in biscuit
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doughs as the reaction with soda is very slow until the dough is
heated in the oven. Much of the reaction between ACP and soda will
occur in the mixer so its effect is not so good during baking because
the gas bubbles produced will be squeezed out during sheeting and
gauging of the dough. There are optimum ratios of soda to each of
these salts but the calculations are confused because the acid salts are
often sold as blends with a diluting material such as starch to make
the metering easier. Refer to the suppliers’ data sheets to find out the
optimum ratio of acid to sodium bicarbonate in a dough.
Baking acids are always sold in multiwall paper bags and they
should be stored in dry conditions.
12.5 Ammonium bicarbonate, ‘Vol’
This is another white crystalline material. It is an extremely useful
leavening agent for biscuits because it decomposes completely when
heated, breaking down into carbon dioxide gas, ammonia gas and
water and thus leaving no residue in the baked biscuit. The name
‘Vol’, by which it is commonly known, derives from ‘volatile salt’
because of this complete dissociation. It is readily soluble but is very
alkaline giving softer doughs which require less water for a given
consistency.
Despite the strong smell of ammonia, both in solid form and in
solution, only a small proportion of the available gas is lost when it is
dissolved in water and held at normal temperatures. Even in solution
for 24 h little of its potency is lost.
It is important that all of the ammonia is driven off during
baking otherwise unpleasant tastes are encountered. Ammonium
bicarbonate is therefore not suitable as a leavening agent in any
products that leave the oven with more than 5% moisture, e.g.
cakes and sponges.
In many cases it has been found satisfactory and convenient to
eliminate all acidulants in biscuit doughs and to use only Vol and
soda. The soda is there primarily as a means of controlling the acidity
of the baked biscuit.
Vol is purchased as a white crystalline solid in paper or plastic
bags. It is prone to severe lumping even when stored in dry
conditions. It should, therefore, be used as soon as possible after
delivery.
Chemicals 73
12.6 Fruit acids
Food acids are organic acids found in natural products but now
normally manufactured by chemical synthesis. They are all white
crystals or powders. In biscuits they are used mainly to accentuate
fruit flavours in sandwich creams but they also have a technical
function in jams and jellies in that they control the setting of
pectin.
There are three commonly used food acids in biscuits. These are
citric, found in oranges and lemons, tartaric, found in grapes and
malic, found in apples.
Citric and tartaric acids have a similar taste giving an immediate
sharp sensation which is not persistent. Malic is less strong initially
but is more lasting. The selection of acid for use in biscuit creams
will probably be made primarily on the basis of cost. To achieve a
good spread of acidic sensation finely ground acid powder should
be used. If the acid has caked during storage it should be sieved
before use.
12.7 Sodium metabisulphite, 'Natron'
Sodium metabisulphite (SMS) or Natron is another white crystalline
powder. It is used in very small quantities to modify the gluten
quality chemically in semi-sweet biscuit doughs. It behaves as a
reducing agent through the liberation of sulphur dioxide gas
(unpleasant smell) when in solution. It causes the gluten to become
more extensible and less elastic and therefore reduces the shrinkage
of dough pieces as they are baked. It is a useful processing aid to
compensate for the variations in gluten quality that are encountered
from month to month and year to year.
As only small amounts are used in a dough it is normal to use the
salt as a solution in water. A 10% solution is commonly prepared.
Solutions should be used within a day. The normal level at which
SMS is used in doughs is up to 50 g per 100 kg of flour.
SMS is not universally permitted for use in baked foods. There is
concern about the effects of sulphur dioxide on human metabolism.
Research has shown that in biscuits, residues of SMS der baking
are extremely small and difficult to find. The possibility of health
risks from this valuable processing aid are therefore probably
negligible.
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12.8 Emulsifiers
Emulsifiers form a large group of compounds whose function is to
stabilise mixtures of two immiscible liquids. In the food context, the
immiscible liquids are normally oil (fat) and water. Emulsifiers are
effective at very low levels (less than 2% of the recipe weight) and so
are classed as minor ingredients or food additives. In biscuit doughs
an emulsifier permits the easier blending of a fat in the dough and
this effect also gives the possibility of reduced fat usage to obtain
similar biscuit textural properties.
Most emulsifiers are synthesised chemicals and there are legal
restrictions for their use in food. Naturally occurring emulsifiers are
few and only lecithin, derived principally from soya bean, is in
common usage. However, for about 50 years the value of specially
prepared monoglycerides, such as glycerol monostearate, products of
fat refining, have been used. Glycerol monostearate is a white flaky
substance.
Lecithin is a natural food substance which occurs in all living
matter but is found in significant quantities in egg yolk (&lo%) and
soya beans (2.5%) which is the main source of vegetable lecithin. It is
extracted from the beans by solvents, but varies in composition and
always contains a sizable percentage of soya oil. It is a fluid or a
plastic paste which, if used in excess, imparts unpleasant flavours to
baked products. It is normally supplied in steel drums.
The usage rate is normally between 0.5-1.0% of the fat but
quantities up to 2% are not unusual. Soya lecithin is not soluble in
water but dissolves in warm fats and oils. It is, therefore, convenient
to dissolve the lecithin in the fat before this is added to the recipe.
Purified and modified lecithin is also available as a powder.
Typically this is a 50% mixture with skimmed milk powder or
lactose. In this form it may be dispersed in water directly.