Yeast and bread
Bread, and the “baguette” or stick in particular, is considered to be the ultimate traditional French food.
Made with flour, water and salt, bread is now eaten all over the world. But to obtain light, well-risen bread with an airy crumb, another ingredient is indispensable: yeast!
Yeast: a key ingredient!
During fermentation in bread-making, yeast produces carbon dioxide and modifies the physical properties of dough through the action of enzymes.
During normal fermentation of bread dough consisting of water, flour, salt and yeast, there are three distinctive phases.
- Firstly, yeast ferments sugars which it directly assimilates and are naturally present in flour (about 1.5% of its weight).
- The second phase corresponds to the fermentation of a sugar found in flour called maltose. Maltose results from the action of certain enzymes, amylases, on flour starch and which is damaged when milling the wheat. When the dough contains added sugar, saccharose or glucose, this is directly fermented before maltose. In a product like brioche, saccharose is mainly consumed by yeast. The other unconsumed part helps to give a sweet taste to the product. The action of flour amylases is completed by that of another yeast enzyme, maltase, which then breaks down maltose to produce the simplest sugar form, glucose. Glucose is transformed by yeast into carbon dioxide (which gives volume to bread and the honeycomb shape of the crumb) and into alcohol (evaporated on baking). Yeast also produces aromatic compounds that contribute to the aroma and taste of bread.
- The third phase occurs during baking. Fermentation is activated by heat and ends when the temperature reaches 50°C.
To enhance flavours:
“Food yeasts” are inactive yeasts used for their taste and their nutritive value. Thanks to their sapidity agents, aromatic notes and minerals, these yeasts are flavour enhancers. They are also used to improve the texture of low-fat products but also reduce acidity and bitterness. They have an impact on the aroma of the crumb via secondary fermentation products. Yeasts play a major role in colouring bread crust.
The development of yeast in bread dough
Yeast is a living organism that needs a favourable environment, food and water to develop:
- Its food: Yeast is mainly nourished by sugar molecules that it finds in flour included in the bread recipe.
- Water: It is mainly found in flour and in the water added to make bread dough. Without water, there can be no fermentation.
- The environment: the medium into which yeast is introduced is important as its physical and chemical composition needs appropriate salt content and temperature ranging between 10°C and 30°C.