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 which has been
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 in bread-making 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:
- mixing the ingredients to make a dough
- kneading or beating the dough
- rising
- knocking back
- shaping
- baking.
When the ingredients have been mixed together, kneading is
required to help the protein (gluten) to soften and strengthen the dough. After
kneading, the dough is left to
rise (or 'prove') to double its original volume, as the yeast
cells multiply and produce carbon dioxide gas. The yeast multiplies at different
speeds in different temperatures, so the 'rising time' depends on where the
dough is kept. The dough would 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.
When the dough has risen, it must be knocked back before
shaping. The large air bubbles produced by the yeast are knocked out of the
dough to ensure a more even texture and a better rise. Large bubbles of gas
would make large holes in the finished bread.
After knocking back, the dough is shaped and may be put in a
tin. It is then covered and left to prove, or rise, again. Proving times will
vary with the temperature and volume of the dough, e.g. 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.
The dough is ready for baking. The yeast has done its job,
and now a very hot oven is needed to kill off the yeast cells. Basic bread
doughs are normally baked at 230°C (450°F, gas mark 8). The baked bread should
be well risen, golden and crisp; it should sound hollow when you tap it on the
base.
