Cake Flour Is Not Just Any Old White Powder: A Fun Take-Home Experiment
Baking cakes with different recipes can provide an exercise in the application of the scientific method, illustrating the need to vary only one ingredient at a time for correct derivation of conclusions. This experiment, most likely to be performed at home, compares a cake flour with flours from durum wheat, rice and cornflour (gluten-free starch). It leads into discussions about the chemistry of gas production in baking, about the taxonomy (relatedness) of cereal-grain species and about the nutritional aspects of baked goods, especially for people with wheat (gluten) intolerance.
Wheat flour is used to make the many food products listed in Figure 1. Pasta, for example, is best made from flour (semolina, a coarse flour) milled from very hard durum wheat with a high protein content (about 14%, mainly gluten). On the other hand, low-protein flour milled from soft wheat is favoured for cake and biscuit manufacture.
For general home baking, the flour available from the supermarket is suited to cake making--rather low in protein content (8% protein or so) and from soft wheat thus having low starch damage. Baker's flour is indicated in Figure 1 to require moderately high protein content made from hard wheat; the consequent starch damage means that more water is needed to make a dough from baker's flour than for cake flour.
Flours made from other cereal grains, such as rice, are not so well suited for bread or cake baking because they do not have the gluten protein that is unique to wheat. The same goes for cornflour, which is the starch part of wheat flour with the gluten protein removed by water washing (see Wrigley, 2012). Although the product called 'cornflour' in the supermarket is often made from wheat flour, it may alternatively be the starch from corn (maize). In the UK, the word 'corn' may mean any grain.
Bread and cake are characterised by their light fluffy texture due to many air holes (thus you might say that they are 'wholesome'). For leavened bread, the holes are made by carbon dioxide (C[O.sub.2]) production from yeast. In contrast, 'chemical leavening' is used for cakes.
Self-raising flour is cake flour that includes chemical raising agents, namely, some form of 'baking powder'. The most common form of baking powder is a combination of sodium bicarbonate ('bicarb' or sodium hydrogen carbonate, with the formula NaHC[O.sub.3]) and 'cream of tartar' (a weak acid, potassium hydrogen tartrate, with the formula KH[C.sub.4][H.sub.4][O.sub.6])
When this combination is mixed with water and heated, carbon dioxide (C[O.sub.2]) is liberated according to the following equation:
NaHC[O.sub.3] + KH[C.sub.4][H.sub.4][O.sub.6] [right arrow] KNa[C.sub.4][H.sub.4][O.sub.6] + [H.sub.2]0 + C[O.sub.2] [up arrow]
In this experiment, commercial baking powder is suggested as the raising agent. So how different in function are these various types of flour for cake baking?
To determine the effectiveness of different types of flour in cake baking.
Cake flour (milled from low-protein soft wheat flour) is better suited for cake baking than are other flour types, especially flour from a non-wheat cereal.
The experimental strategy in Figure 2 is to compare the suitability for cake making of flours from common wheat, from durum wheat, from rice and a gluten-free flour. Only the flour type is altered. All other ingredients and the method are kept the same throughout. [That is how an experiment should be conducted--altering only one factor at a time.] However, to optimise the conditions, it may be necessary to adjust slightly the amount of liquid added to the batter and the cooking time.
According to the strategy of Figure 2, four flour samples are needed: