One of the most common physicochemical phenomena in the kitchen is the leavening of the dough.
Leavening agents are those substances that release gases and cause the risen of dough during baking or frying.
To understand how the dough is rising, we need to understand what happens when flour is mixed with liquid ingredients.
Wheat flour contains besides starch two proteins: gliadin and glutenin. During the kneading, in the presence of water, these two will form the gluten and this it is responsible for the elastic structure of the dough.
The gas bubbles formed by the leavening agent remain trapped in the gluten structure and as the temperature rises during the baking process, they increase the volume. When the temperature rises, even more, the gluten coagulates, the starch becomes gelatinized and form the fluffy structure characteristic to pastry and bakery products.
The gluten coagulates starting about 38°C but finishes to coagulate between 70°C and 80°C.
In dough without gluten (or not kneaded), such as those based on whipped egg whites, the protein structure is formed on the base of egg albumin.
The egg white coagulates between 60°C and 65° C.
Although essentially the mode of action is the same, the expansion of a gas that causes the rise of dough, the leavening agents are divided into three main categories:
It is generally used in chiffon cakes and sponge cakes and it is still met in the case of flat, unleavened bread.
Up to a point we can talk about an isobar transformation.
Vf - Final volume
Ti - Initial temperature (°K)
Tf - Final temperature (°K)
When the dough water begins to evaporate and the mass of gas increases, the volume increases even more.
1 mol of water = 18.0152 g = 30.6 liters of water vapor at 100° C.
Then we are also talking about an isobar transformation.
At temperatures above 65°C, sodium bicarbonate decomposes and forms carbon dioxide.
The chemical reaction is as follows:
The reaction of sodium bicarbonate with acids is used for this. Citric acid, tartaric acid, vinegar, lemon juice, fruit juice, etc. are commonly used.
Sodium bicarbonate reacts with acid (acetic in the equation below) as follows:
The first phase results in sodium acetate and carbonic acid.
Double action baking powder has two or more acids, one reacts at room temperature, while the other react only when it is heated.
It is the ammonium salt of carbonic acid.
By heating them to above 36°C decomposes according to the reaction below:
Yeasts are unicellular microorganisms in the fungus class.
The most important yeast for dough leavening is Saccharomyces cerevisiae.
Yeast breaks down sugars in two ways:
If you didn't know, now you know how the dough rise!
