Fermentation should take 3 to 4 hours, until the dough doubles its volume. Fermentation time depends on the temperature and the activity of yeast in the starter.
During fermentation gluten is gradually stretched into strands which form the structure of porous dough. The process starts at the moment of the first contact of wheat flour with water and ends when gluten strands are fixed during baking in the oven. Meanwhile, gas produced during the fermentation process will give the bread its structure, forming irregular bubbles which give the cross-section of the loaf its magnificent look.
You can imagine individual yeast cells munching on starch and producing, among others, alcohol and carbon dioxide in the process. Alcohol is captured by starter bacteria which produce lactic and acetic acid and other substances giving your bread its delicious flavour and aroma, as well as carbon dioxide which inflates the numerous gluten bubbles.
Throughout the entire bread-making process, the dough yeast and bacteria live very active lives. Their activity can be controlled by temperature. Yeast activity is fostered by higher temperatures and inhibited by lower temperatures – this is when bacteria come into play. Therefore, later on (during retardation) we will leave the dough in a fridge for several hours. But first, let’s mould the loaves.