We all knead flour at home to make rotis or chappatis. It seems like such a routine activity that we dont consider it to be a chemical reaction anymore. We have noticed before that when dough is kneaded too long it becomes elastic, we always rest the dough for sometime before using it, why do we follow these steps ?
Here is an attempt to answer these questions. We start with a simple dough that is made by kneading wheat flour with water and go on to understand how yeast acts on dough to give us the delicious bread we eat everyday.
When flour is mixed with water the proteins present in flour – Glutenin & Gliadin, grab water and each other to form an elastic mass of molecules called ‘Gluten’.
The more you knead the dough stronger the gluten bonds become.
Let the dough rest for sometime before making bread or
rolling it out into rotis/chappati
When the dough is allowed to rest the gluten bonds relax
making it easier to give shape to the dough.
Leavening is the process of adding gas to a dough before baking to produce a bread that is light and easy to chew.
Stir yeast with sugar in warm water until it
dissolves.
Yeast cells feed on sugar and get activated.
Yeast metabolizes sugar to produce CO2 and
ethanol.
Warm water is used because optimal temperature for yeast to ferment sugar is 32 ° C.
The yeast mixture is now kneaded with flour to prepare a dough
Kneading helps distribute the yeast evenly
throughout the dough hence strengthening the
gluten bonds.
The more the dough is worked upon, the chewier the end product will be. This would be desirable for bakes like bagels, pizza crust or French bread.
Bread that has not been kneaded enough tends to be crumbly and falls apart easily due to weak gluten bonds.
The by-product ‘Ethanol’ is an alcohol that contributes to the bread’s flavor.
The dough is now allowed to rest. In about an hours time it doubles up in volume.
If the dough has a strong gluten network the produced CO2 is trapped in the dough in the form of tiny bubbles and the dough begins to inflate.
Each Co2 bubble helps more protein find water, hence forming more gluten. Its almost like kneading at the molecule level resulting in a stronger gluten network.
The dough is now punched down and kneaded further with light hands
Punching down the dough releases the large
CO2 bubbles. If the gas is not allowed to
escape you will end up with yeasty flavored
bread! Kneading further causes the gluten
bonds to strengthen.
Now allow it to rest for a short while so that the gluten bonds relax and it will be easier to shape the bread.
Give the desired shape to the dough and
let it rest for a short while till it puffs up.
This is to complete any yeast activity
before the dough goes into the oven.
Once in the oven, yeast will become
completely inactive as yeast cells die at
around 45 °C.
The enzymes in the flour that were assisting the break down of starch also become inactive now.
Once the bread is done you can tap the bottom of the bread can. If it sounds hollow the bread is ready, else it needs to be baked further.
Certain breads appear more brown on baking than others. There are a couple of reasons behind that :
1) Wheat flour breads are naturally browner than breads made with white flour.
2) If milk was used in the dough you will get a browner bread. Milk contains lactose, a sugar that yeast can not act on. Hence, lactose is available for browning. The color change starts when its heated to about 175 °C.
Dough that doesn’t contain milk can be refrigerated up to 3 days. However, if it has milk then its shelf life is reduced to 2 days.
There is another case of bread making where you intentionally refrigerate the dough and bake it later as the bread seems to have a better flavor this way.
The reason behind this change of taste is that at low temperatures bacteria begins to act on the dough. Yeast does not die at low temperatures, rather its activity reduces giving bacteria a chance to feed on the sugar and produce flavorful acids. This process of bread making is also known as ‘Cool Rise’.
If the dough is stored for too long the CO2 released by slow yeast action, along with the acids produced by bacteria will cause the dough to turn sour.
