THE SCIENCE OF BAKING

The basic ingredients of bread are:

• flour
• yeast (to make the bread rise)
• salt (to add taste and aid proving),
• vinegar (a preservative)
• vegetable fat (to make the loaf lighter and airier and extend its shelf life)
• water.

All white bread sold in the UK is made with white flour fortified with calcium, iron and B vitamins.

Yeast

Almost all breads today are leavened, which means that a substance has been added to the dough to start fermentation and make it rise. The most popular and widely known leavening ingredient is yeast.

Yeast is a micro-organism, one of the tiniest forms of life. The air around us is full of thousands of different kinds of yeast. If it is given warm, damp surroundings and starchy or sweet matter, it will start to breed. As the yeast multiplies, it turns starches and sugars to alcohol and produces carbon dioxide gas. It is this gas that adds the air into the dough, and makes it increase in size.

The yeast used by bakers is called Saccharymosa cereviserae. It was originally a by-product of brewing beer (when the yeast was used for the alcohol, rather than the carbon dioxide, it produced). Today it is cultivated commercially in laboratory conditions, and sold as fresh, compressed or dried yeast.

Yeast must be mixed with a warm liquid before adding it to flour. If the liquid is too cool, the yeast won't multiply; if it is too hot (over 43°C), the yeast will be killed.

Protein

The important protein found in flour is gluten. Gluten gives the dough softness, so that it can expand when the gas bubbles produced by the yeast form. It also gives the dough strength so that the gas bubbles do not burst.

The stages of baking

All mixtures made with yeast are prepared in several distinct stages:

Ingredients are mixed to make a dough

Next

Dough is kneaded to help the protein (gluten) soften and strengthen the dough.

Next

The dough is left to rise (or 'prove') to double its original volume, as the yeast cells multiply and produce carbon dioxide gas. The 'rising time' depends on where the dough is kept (double in size in about 1 hour in a warm place, 1–2 hours in a cool place, and up to 12 hours in a refrigerator).

Next

The dough is knocked back to remove the large air bubbles produced by the yeast. This ensures a more even texture and a better rise. Large bubbles of gas would make large holes in the finished bread.

Next

The dough is shaped and may be put in a tin. It is then covered and left to prove, or rise, again. The time this takes will again depend on the temperature and volume of the dough. In a warm place, a large loaf may take 50 minutes to rise, while rolls will take 25 minutes. When proved, the dough will be light, puffy and doubled in size.

Next

The dough is ready to be baked. A hot oven (230°C, 450°F, gas mark 8) is needed to kill off the yeast cells. The baked bread should be well risen, golden and crisp and should sound hollow when you tap it on the base.

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