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. 70 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 72 Biscuit, cookie and cracker manufacturing manuals 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. 74 Biscuit, cookie and cracker manufacturing manuals 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.