Types of Dough
The basic ingredient of nearly all biscuit doughs is flour. To this is added sugar, fat and possibly a wide variety of other ingredients. The dough is bound together with water. As more fat is included in the recipe less water is required.
After mixing, the dough is divided up into small pieces of particular shape and size. These pieces are baked into biscuits. Whether the dough is processed into pieces by machine or by hand the consistency is very important.
The consistency, the feel, of dough is determined principally by the amount of water present and also by the temperature of the dough. Wetter and warmer doughs are softer. The mixing of water with flour involves a number of changes but basically the hydration of the components of the flour is a relatively slow process. This means that some change, which affects the dough consistency, may continue to occur after the mixing has been completed. Thus, when considering the making of a biscuit dough one must think not only about what happens in the mixer but also in the period afterwards.
There are basically two types of biscuit dough, hard and short. The difference is in the consistency which in turn is determined by the amount of water available to hydrate the flour. When there is a high water content (and therefore a relatively low level of fat) the blending with the flour involves the formation of gluten from the hydrated proteins. The formation of gluten requires mechanical work, kneading, and thus we say that hard doughs are "developed" doughs, referring to the mechanical action. When the quantity of fat is higher the amount of water is less and the mixing is designed so that little or no gluten is formed as the flour hydrates, this is called a short dough.
Hard, or developed doughs, are used to make crackers and semi-sweet biscuit types. The fat and sugar levels are relatively low. In all cases sustained mixing action is required, to develop the gluten. In the case of cream crackers and soda crackers the gluten is further modified after mixing during a period of fermentation with yeast. However, for semisweet biscuit dough all the gluten development takes place in the mixer and the mixing time is relatively long.
Dealing firstly with cracker dough that is to be fermented. The yeast cells are a living fungus and the speed of their growth and action to produce carbon dioxide gas is determined very largely by the temperature. It is therefore most important, in the first instance, that the dough is mixed to the desired final temperature (usually a value between 26 and 30°C). This can be achieved both by the length of the mixing time (during mixing a dough warms up through friction) and by the temperature of the ingredients (particularly the water) used.
In some cases cracker doughs are remixed after a period of fermentation and at this time more flour and water is added.
Other cracker doughs involve the use of an enzyme, known as proteinase, which chemically modifies the gluten during a standing period after mixing. The reaction is not too dissimilar to fermentation by yeast as living cells all use enzymes to effect metabolism, however, in this case no gas is produced. The temperature of the dough is again important as the speed of chemical reactions is very sensitive to temperature. The temperature of proteinase doughs is usually about 35°C.
Typically all types of cracker doughs are mixed in only one stage of mixing. All the ingredients are loaded into the mixer and the mixing proceeds. This is known as an "all in" mix procedure.
Puff doughs are a special type of developed dough. In the course of dough piece forming a laminated structure must be developed and the layers are separated by soft, semisolid, plasticised fat. The fat must be maintained cool which means that the dough must also be cool or cold. Thus, puff doughs must be mixed and stood so as to maintain low temperatures (usually around 15°C or less). Iced water will be used at dough mixing and a chilled room is required to hold the dough and in which to make the laminations.
Semi-sweet doughs are rather different from cracker doughs. They have appreciably more sugar and fat in the formulation and they are not fermented after mixing. A considerable amount of work is needed to get the gluten into an optimum condition. Much research has been done to determine conditions that produce a well mixed dough. The conclusions are that doughs should be mixed to a specific final temperature, and provided that the mixing time is above a low minimum (about 4 minutes), the time to produce the mix is not critical.
In many cases the gluten quality is additionally modified, during mixing, by using a small quantity of the chemical sodium metabisulphite.
The use of sodium metabisulphite, SMS, has a dramatic effect on the dough quality. Compared with doughs with no SMS the amount of water needed is reduced by 10% or more. The SMS reduces the elasticity of the gluten so the dough shrinks less after cutting. It is therefore easier to control the shape of the biscuits baked from the dough. By adjusting the amount of SMS used some variations in the quality of the flour can be compensated for.
Typically semisweet doughs are mixed in only one stage of mixing. All the ingredients are loaded into the mixer and the mixing proceeds.
A variety of semisweet doughs where the amount of mixing is much less is referred to here as "Continental" semisweet. This is because the method is commonly used in France, Switzerland and Germany but not in the UK and many other countries.
These doughs are mixed in a two stage process. Firstly all the ingredients except the flour are put into the mixer and mixed to a homogeneous cream. The flour is then added and a second mixing proceeds for only a few minutes. The dough is then rested for 30 to 90 minutes to allow the flour to hydrate and for the stickiness to reduce. Thus continental semisweet doughs are more like low fat short doughs.
Short doughs and batters
As a group, short doughs vary very greatly in their formulations. In no case is the hydrated flour protein developed into cohesive gluten. The dough pulls apart easily, there is minimal elasticity and extensibility, and is said to be "short". The formation of gluten is hindered or very limited because the level of fat is high and the level of water low.
The challenge in making a short dough is to disperse the fat and water evenly through the flour and prevent the hydrated proteins forming gluten. Normally this is achieved by firstly forming an emulsion of the fat and the water and then mixing this quickly with the flour. In the first stage of this procedure the sugar and most of the other ingredients are also added. This allows the sugar to dissolve in the water and all ingredients to become well dispersed. Often the level of sugar is too high for it to dissolve completely in the available water and undissolved crystals of sugar will be an important part of the texture of the baked biscuit.
Typically the first stage will take several minutes of mixing but the time is not critical. There is little or no development of heat as the mixture is very soft. The second stage, after addition of the flour, will be very short, perhaps as little as one minute, depending upon the efficiency of the mixing action. The time is very critical to prevent the development of gluten and thus toughening the dough.
It will be appreciated that during the second stage of mixing there is insufficient time for the water to become totally absorbed into the flour. Hydration continues passively after the mixing has finished. This means that the dough is much softer at the end of mixing than it is after 30 minutes standing. This change must be allowed for in the dough handling before rotary moulding or sheeting.
Some short doughs are very soft and even pourable.
The temperature of short doughs is determined largely by the temperature of the flour, sugar and fat. There is little possibility of controlling or adjusting the temperatures of the flour or the sugar but the fat is normally used soft at up to 26°C. A small amount of dough temperature control can be achieved by using cold or warm water and by holding the jacket of the mixer at a desired temperature. The ideal temperature for a completed short dough is between 18 and 22°C.
Some "biscuits" are made from very fluid batters, normally these are based on egg and are really variants of cake formulas. These batters are mixed with high sheer mixers in order to incorporate air bubbles which form the basis of the baked structure.