Utilisation of Yeast for baking

Bread came into being from observations made by the Egyptians 3,000 years ago of the transformation of the dough by beer froth which they scooped up from the surface of bowls. Since then, the history of bread, yeast and men is tightly linked. For a long time, bread was a basic food element in Europe and in the whole Mediterranean basin, with a high symbolic content.

Without fermentation by yeast, a living and natural product, we could not obtain the equivalent of bread or Viennese pastry.

Bread is less important nowadays as a basic food in developed countries, but it is still a healthy product, harmoniously helping to bring about a balanced diet and nutritionists recommend its consumption.

Baking fermentation

0710I02 Petrissage a la main

In the process of fermentation, yeast produces carbon dioxide, alcohol and other compounds which enable dough to rise and modify its physical properties. When the fermentation is correctly achieved, depending on the quality of flour among other things, the baker will obtain the proper external and internal characteristics (grain and texture) suitable for a determined finished product.
Together with alcohol, a small amount of other volatile compounds are released. These are involved in the original taste and flavours of baked leavened products. Most of these compounds, and all of the alcohol, evaporate when baked.

There are two stages during the fermentation of a dough made from flour, water, salt and yeast, and with no extra sugar added.

First of all, yeast ferments sugars naturally present in flour, which can be directly and easily assimilated. These sugars represent about 1.5% of the flour weight. At the end of this first stage, gaseous releases more or less slow down.

The second stage corresponds to the fermentation of a sugar contained in flour called maltose. Maltose comes from the action of some enzymes, the amylases, on the starch granules of the flour, damaged during the milling process. Amylases which are naturally present in flour, split starch into small fractions of a much simpler sugar, the maltose. The action of amylases starts as soon as water is added to the flour and stops during baking.

The action of the flour amylases is completed by that of another enzyme of yeast, the maltase which, in its turn, splits maltose to give the most simple sugar, glucose. The glucose is transformed by the yeast into carbon dioxide and alcohol.

Maltose formed from starch must be present in sufficient quantity so that the production of carbon dioxide makes dough rise correctly until it is put in the oven.

Since 1960, the bakery industry has benefited from better adapted yeast strains, allowing a rapid process as they ferment the maltose sugar earlier. Effectively, the maltose is fermented only when there are no or little pre-existing sugars or added simple sugars left in the dough.

The yeast industry has studied to a great extent baker’s yeast strains, not only with a view to making them more rapid, but also to adapt them as much as possible to different types of baking processes.
If sucrose has been incorporated into the dough, it is immediately transformed by a yeast enzyme, the invertase, into glucose and fructose (the two basic links composing sucrose are thus separated).

When sucrose or glucose are added to the dough, they are directly fermented before maltose. This means that in such a dough, mainly sucrose or glucose are consumed by the yeast. These sugars do not contribute to giving the bread a sweet taste since they are partly consumed. 

Use of yeast

The Dosage of Yeast
For breadmaking, the amount of yeast used is between 2 and 5 kilos of compressed yeast for 100 kilos of flour. In practice, this proportion varies effectively according to the baking process and the temperature of the bakery.
In 100 grams of flour, 1 to 10 million micro-organisms live among which only 30,000 are the so-called wild yeasts. A standard amount of 2.5 grams of baker’s yeast for 100g of flour provides 25 billion yeast cells. This is the proof that baker’s yeast is predominant in the bakery fermentation.

Fermentation begins as soon as the yeast is in contact with the mixture of water and flour. During the first fermentation (bulk fermentation), the baker lets the dough rise for a first time. During that stage, the physical properties of the dough (extensibility and elasticity) are modified, thus completing the kneading action.
This is an important stage on which depends the final quality of the bread: external and internal characteristics, taste and aroma.
The mechanisation of the division of the dough requires some rest so that the dough pieces may relax before moulding, in order to recover some extensibility.
The fermentation process goes on in the cut lumps of dough during the proofing which can be made on layers, on flexible nets or in moulds, in cupboards at ambient temperature or in proofing ovens. In order to prevent the lumps of dough drying out during this stage, they must be covered so as not to hinder the development and the appearance of the finished product.
This stage can be achieved by a cold-controlled fermentation, in chambers in which temperature and degree of humidity (hygrometric degree) are determined with precision. Thus, the fermentation can be controlled and working hours organised.
In the case of French bread, the baker makes small and regular blade incisions in the lumps of dough just before putting them in the oven. These incisions will give nice edges, the puckering, on the crust of the bread. It is a delicate operation requiring much experience: it is said that it is the baker’s signature because it essentially depends on his know-how.
Without these blade incisions, the loaf of bread loses its shape and bursts under the violent release of the carbon dioxide and steam which appear right after being put into the oven. The blade incision is therefore not made for decorative reasons only, but it also gives the loaf a regular aspect by creating a zone where the dough will be torn in the right direction. Thus, the loaf gets a regular volume and an optimal development.

Science and history

Bakers know two ways of getting dough to rise :
the first one, only for biscuits and cakes, is the use of a chemical powder which makes dough expand as soon as it is put into the oven ;
the second one, for bread and Viennese pastry, is the use of natural living yeast which requires fermentation before it is put into the oven in order for the dough to develop.

The use of chemical powder may seem more simple and convenient, but its use is not appropriate for bread making. On the one hand, carbon dioxide is not produced in sufficient quantity to obtain a light and alveolated bread texture and, on the other hand, only a fermentation agent like yeast can give bread its organoleptic quality.     

Bread is symbolical food which, in spite of its various compositions, is appreciated worldwide thanks to a special manufacturing process : fermentation.

Between 1857 and 1863 Louis Pasteur demonstrated the role of yeast as a micro-organism responsible for fermentation.

" All yeast which ferment bread, beer, wine and cider correspond to microscopic living cells of a microscopic fungus, Saccharomyces cerevisiae.
Many varieties of Saccharomyces cerevisiae exist in nature and they are more or less suitable for the various types of fermentation".