The main ingredients for biscuit making are flours, sugars and fats. To these ingredients, various small ingredients may be added for leavening, flavour and texture.
1.1. Wheat flour
The principle ingredient of biscuits is wheat flour. The grain consists of bran (12%), which is the outer husk, endosperm, which is the white centre (85.5%) and the tiny germ (2.5%). Typical biscuit flour is milled to a yield or extraction of 70-75%. Wholemeal flour is of 100% extraction and wheat meal flours in between these extraction rates, normally around 84% extraction. The flour will also contain moisture of between 13 – 15%.
The wheat flour is composed of carbohydrate (as starch), protein and fat, together with some fibre, ash and trace minerals and vitamins. The protein is mainly gluten, composed of gliadin and glutenin.
The percentage of protein determines the flour strength. A dough made from strong flour with a high protein content, is extensible and can be machined into a continuous sheet for crackers and hard biscuits. A weak flour with a low protein content produces a short dough which may be moulded or a soft, high fat dough which may deposited on the baking band and when baked, gives tender cookie.
1.2. Wheat gluten
The formation of the gluten, its strength and elasticity are largely determined by the flour specification, recipe and the mixing and forming processes. Wheat flour contains proteins including gliadin and glutenin. In the presence of water these proteins combine to form gluten. As the dough is mixed the protein molecules form long strands of gluten, which have strength and elasticity. The gluten forms an elastic web, which gives the dough strength and allows it to be machined into a thin sheet for crackers and hard sweet biscuits. These biscuits are made with “strong” flour, which has a high protein content, typically 10-12%.
The gluten web is also important in trapping air and gas bubbles formed by yeast fermentation or by leavening agents such as sodium bicarbonate (“soda”) or ammonium carbonate (“vol”). This leavening process, combined with the laminating of the dough, gives the characteristic open, flaky texture of crackers during baking.
Soft or short biscuits are generally made with low protein flour (7-9%). A low protein flour makes a dough with a much weaker gluten web. In addition these doughs have higher fat contents. The fat coats the flour particles and this inhibits the hydration of the proteins and the formation of the gluten web. Shorter mixing times also result in less development of the gluten strands and hence the biscuits have a short texture.
Starch is the main component of wheat flour. It represents almost all of the carbohydrate content and around 80% of the total energy content of wheat flour. Starch is a polysaccharide (many sugars) made up of glucose units linked together to form long chains. The principle starch molecules in wheat flour are amylose, which typically comprises 28% of the total amount of starch. Amylose molecules contribute to gel formation. Their linear chains of molecules line up together and are able to bond to make a viscous gel.
Starch is insoluble in water, however the starch granules do absorb a limited amount of water in the dough and swell. Above temperatures of 60o-70o C the swelling is irreversible and gelatinisation begins.
The gelatinisation may continue until the starch granules are fully swollen, but it is normal in baked products that only partial gelatinisation occurs. The gelatinisation of the starch contributes to the rigidity and texture of the biscuit.
As the starch gel is heated further, dextrinisation occurs. This contributes to the colouring of the biscuit.
In soft dough products, the high sugar and fat content of the dough inhibits starch gelatinisation. The presence of sugars delays the gelatinisation of the starch, which may be due to the competition for water. The fat, composed of triglycerides and surfectants, also tends to inhibit gelatinisation. With high sugar and fat recipes, the dough has a low gel viscosity and strength and produces short and soft biscuits and cookies.
1.4. Corn flour
Corn flour is a white free flowing powder produced by wet milling of maize, followed by washing, concentrating, centrifuging, drying, milling and sifting to give a natural maize starch. It has a short gel texture, relatively high viscosity and is easily dispersed in cold water.
The protein in corn flour does not form gluten, and it can be used as an ingredient to produce a more tender biscuit with reduced gluten development.
Common sugar (sucrose) is a carbohydrate derived from sugar cane or sugar beet. It is a disaccharide composed of two monosaccharides, a molecule of glucose joined to a molecule of fructose. Sugar is used in biscuit formulations in a granulated or powder form.
Sugar gives sweetness, but it is also important in developing the texture of the biscuit. Dissolved sugar tends to inhibit starch gelatinisation and gluten formation and creates a biscuit with a more tender texture. Undissolved sugar crystals give a crunchy, crisp texture. Sugar crystals, which melt during baking, cool to a non-crystalline glass-like state which gives a crispy, crunchy texture, particularly on sugar topped biscuits.
Dry sucrose melts at 160oC – 186oC. Biscuits with sugar toppings which are melted to a smooth, shiny surface require high intensity flash heat at the end of the oven to fully melt the sugar.
Invert sugar syrup is a mixture of glucose and fructose. The sucrose is split into its component monosaccharides by hydrolysis. The sucrose in solution is heated with a small quantity of acid such as citric acid. After inversion the solution is neutralised by the addition of soda. The invert syrup is sweeter than sugar and it contributes to a moist, tender texture in the biscuit.
Other reducing sugars are included in biscuit formulations in syrup form, for example glucose syrup, malt extracts, honey. The reducing sugars in the presence of amino acids produce the Maillard reaction which contributes to the colour of the biscuit.
Moisture content: 0.06% maximum
Ash content: 0.03% maximum
Powdered sugar: 60μm
Crystal sugar: 150μm
Caster sugar: 150 – 450μm
Granulated sugar: 450 – 600μm
Brown sugar, a dry golden brown sugar with bold crystals.
Particle size: 0.8 – 1.2 mm
2.2. Glucose syrup
Glucose syrup (C6H12O6) is a solution (up to 80%) of glucose (dextrose), maltose and maltodextrins in water. It is normally obtained by enzymatic hydrolysis of starch. Starch from wheat, corn, potato, cassava or any other plant can be used for this purpose.
Standard glucose syrup has a DE value (dextrose equivalent) of 42. The relative sweetness of 42DE glucose to sucrose is 40-45%.
2.3. Cane syrup 80%
Syrups with 80% solids derived from the refining of cane sugar. Used for their excellent flavour.
2.4. Invert syrup 70%
Syrup of 70% solids made by acid hydrolysis of sucrose. The result is a 50:50 mixture of dextrose and fructose which are both reducing sugars and contribute to the Maillard reaction in baking.
2.5. Fructose syrup 80%
Commercially, fructose is usually derived from sugar cane, sugar beets and corn. Crystalline fructose is a monosaccharide, dried and ground, and of high purity. High-fructose corn syrup (HFCS) is a mixture of glucose and fructose. High fructose syrup is a special type of glucose, formulated with a high fructose content. It is much sweeter than glucose.
2.6. Malt extract 80%
A thick glutinous syrup of 80% solids usually non-diastatic and obtained by water extraction of malted wheat or barley. The heat treatment used to concentrate the solution destroys any enzymes. Used as an important flavour ingredient. Rich in maltose, which is a reducing sugar.
3. Dough fats and oils
3.1. Vegetable fats
Fats are a vitally important ingredient in achieving the texture, mouth feel, and the bite of the biscuit. The fats are produced from good quality crude oils by a process of refining, bleaching and deodorising. They are produced primarily from vegetable oils, but may contain hydrogenated fish oils.
Typical blended vegetable dough fats are solid at ambient temperature and melt over a wide temperature range. Most fats used in biscuit making are melted below blood temperature (36.9oC), and this avoids a waxy mouth feel. Fats are specified with a Solid Fat Index (SFI), which indicates the percentage of solid fat present in the total fat. A vegetable shortening typically has an SFI of around 21% at 25oC and 17% at 30oC.
Graph showing melting profiles (Solid Fat Index vs temperature) of various oils and fats Oxford Instruments
Recipes with high fat contents require little water for producing a cohesive dough and produce soft, short doughs. During mixing, the fat coats the flour particles and this inhibits hydration and interrupts the formation of the gluten. Fats also tend to inhibit the leavening action of the carbon dioxide diffusion in the dough during baking and this produces a softer, finer texture. Where both fat and sugar amounts in the recipe are high, they combine to make a soft, syrupy, chewy texture.
Typically crackers and hard sweet biscuit doughs, which are sheeted and cut, have fat contents of 10% – 22% of the flour by weight. Rotary moulded doughs may have 17% – 30% of fat and wire-cut and deposited cookie doughs 25% – 60%.
Butter is used for its shortening and flavour. The flavour of the butter is complemented by sugar and vanilla during baking and gives a distinctive flavour and aroma.
3.3. Coconut oil
Coconut oil is typically used for oils spraying. The oil is hydrogenated, neutralised, deodorised and bleached. Melting point: 32 – 34oC
4. Other ingredients
4.1. Whole egg powder
Whole egg powder is spray dried. Egg yolk is rich in fat and lecithin and it is these ingredients which enhance the flavour and eating quality of the cookie.
Lecithin is an emulsifier produced from soya beans and available in liquid or powder form. It may be added to the fat or directly into the dough mix.
4.3. Yeast (fresh)
A microscopic, unicellular organism. It breaks down sucrose and maltose into monosaccharides and glucose and fructose into alcohol and carbon dioxide. During fermentation, the gas production causes the dough to increase in volume and develops the flavour. Fresh yeast is available as a compressed block. Active dried yeast and instant active dried yeast are other forms.
4.4. Ammonium bicarbonate (“Vol”) (NH4)HCO3
A volatile salt, which is an effective leavening agent. When heated it liberates carbon dioxide, ammonia gas and water.
4.5. Sodium bicarbonate (“Soda”) NaHCO3
The most important aerating agent. When heated, it reacts with acidic materials in the dough to release carbon dioxide and water,
4.6. ACP – Acid calcium phosphate
Acid calcium phosphate is also known as monocalcium phosphate. It is used as a leavening agent in conjunction with sodium bicarbonate and ammonium carbonate.
4.7. SAPP – Sodium Acid Pyrophosphate
Sodium acid pyrophosphate is commonly used in the baking industry as a leavening agent. It combines with sodium bicarbonate to release carbon dioxide.
4.8. Salt (NaCl)
Sodium chloride, used as a flavour enhancer and also to control the rate and extent of fermentation.
4.9. SMS – Sodium metabisulphite Na2S2O5
A reducing agent for the modification of the strength of the gluten in doughs. It causes the gluten to become more extensible and less elastic and so reduces shrinkage of the dough pieces during baking.
4.10. Proteolytic enzyme
Proteinases break down and modify the gluten in doughs, giving a softer, less elastic dough.
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