FAQ on fermentation in baking

Let me answer some questions on fermentation in baking.

Q: Why the dough can't be well fermented well by blending dry active dry yeast with other dry ingredients followed by adding liquid?

A: Firstly, we should know what active dry yeast is. Certainly, it is one of the commercial forms of yeast. It begins as compressed yeast but the press cake is extruded through perforated plates or screens in the form of thin spaghetti-like strands. These strands are cut into elongated pellets as they enter a tunnel dryer and pass through a series of drying chambers maintained at different temperature levels. Drying may also be carried out in rotating drums or in the fluid bed system. The pellets are then ground into small granules or beads. The combination of strain chosen for active dry yeast, the growth conditions, and the drying method tend to favour stability over activity. This means that active dry yeast has lower activity or gassing power than compressed yeast in lean dough. Active dry yeast has lower activity or gassing power than compressed yeast and higher activity or gassing power than instant active dry yeast in sweet dough. Since it is DRY, it is very important to rehydrate this type of yeast before adding it to the other dry ingredients. Some recipes suggest us combine dry yeast with other dry ingredients such as flour, sugar, salt ...etc together directly. The result come out very disappointing -- yeast pellets disperse on the surface of dough and are never dissolved, though wet ingredients are added in the dough too. Therefore, to make active dry yeast more efficient, blend one part yeast with at least four parts lukewarm water, wait ten minutes and stir. The exact definition of lukewarm water can be found on the label of the packet, different products from different companies need different temperature. However, temperature lower than 90F (32C) and higher than 115F (46C) should be strictly avoided.

Q: Why the texture given by fermentation dough wrapped in plastic wrap much better than the dough covered with damp cloth?

A: This relates to the definition of anaerobic fermentation and aerobic fermentation. Anaerobic fermentation is also called ethanol fermentation. In this condition, yeasts convert sugar to ethanol and carbon dioxide. The carbon dioxide causes the air bubbles created in the dough to expand or rise, the alcohol contributes to the bread's flavour, and an organic acid glutamathione, relaxes the dough and gives it more elasticity. This allows it to absorb surface water, making the dough less sticky. Ethanol will be baked out later. In this way, yeast doesn't leave final products or by-products.

Under aerobic conditions, yeasts convert sugar to carbon dioxide, water and cellular mass.

Comparing the two conversion, I don't think anaerobic condition is strictly necessary since both procedures produce carbon dioxide. But I still prefer anaerobic fermentation, because nothing left at all but great taste and structure; and for the production of water under aerobic fermentation, it will affect the structure more or less.

Q: Why fermenting dough in the fridge usually gives very good structure?

A: Generally, the dough is left in a warm draft-free place to rice. Ferment dough in the fridge is called cool rise. It allows yeast to ferment over a long period of time and slow down its rise. Though the cold dramatically reduces yeast activity, the bacteria, who function well even in cold temperatures, now have an opportunity to thrive, producing many more marvellously flavourful acides. On the contrary, an overly warm rising place contributes to an unpleasant beer taste and crumbly loaf.

Q: Except for fermentation, are all the other procedures important?

A: Yes, definitely. Each procedure has its own target:

1) First kneading: Develop a gluten structure (hydrated proteins) in the dough through the application of energy during mixing;

2) Mixing: Incorporate air bubbles as well as fermentation gases;

3) Proof: Ferment and expand of dough or shaped dough pieces;

4) Second kneading: Continue to develop gluten structure in order to modify the rheological properties of the dough and to improve its ability to expand when gas pressures increase because of the generation of carbon dioxide gas in the fermenting dough. This stage also known as "ripening" or "maturing",

5) Baking: Further expand dough pieces and fix final bread structure.