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basic sourdough fermentation concepts

We assume that participants of the workshop: Sourdough Fermentation through Science & Senses, are familiar with the following concepts:

Sourdough starter
A starter is  a natural culture of yeast and lactic acid bacteria that thrive in acidic aqueous environments used to leaven dough.

Bakers percentage
A baker’s percentage is a common dough formula or convention, where the total weight of the flour represents 100%, and all other ingredients are compared or related by weight to that total and expressed as a percentage.

Yeast versus Bacteria in the Sourdough fermentation
We assume – in a very simplified fermentation model – that  yeast produce alcohol and CO2 (carbon dioxide), which leavens the bread, while bacteria are responsible for the production of acids, mainly lactic acid and acetic acid.

Fermentation, Waste products and Stress
Fermentation refers to the growth of microbial organisms, yeast and bacteria. During fermentation these organisms produce metabolic waste products (alcohol, acids, carbon dioxide, etc), which we perceive as flavour but these organisms need to get rid off. Accumulation of waste products in the dough increases the toxic stress for these organisms and reduces the speed of growth.

The pH of an aqueous solution is a measurable scale used to specify the acidity or basicity of the solution. The lower the pH the more acidic the solution is. A pH of 7 is considered neutral. Lower pH values are considered acidic and higher values basic.

Large granules where sugar (energy) is stored by plants. A large part of the – cereal – grain consist of starch. Starch needs first to be broken down by enzymes into smaller units before becoming sweet and fermentable by yeast or bacteria.

Fermentable and unfermentable sugars
There are different kinds of sugars in nature. Bacteria and yeast have preferences for specific sugars, these are referred to as fermentable sugars. There are also sugars that certain microorganisms can not use as a source of energy. For some organisms specific sugars may be unfermentable. For example some people can’t use lactose as a source of energy, they are lactose intolerant, or in case of microorganism such a sugar would be unfermentable. Sourdough contains many different organisms, implying that most sugars normally can be fermented by a wide range of microorganisms.

A class of molecules that reduce the pH in an aqueous solution, and taste sour.
Acids are formed when fermentable sugars a broken down by enzymes to release energy, 

A class of large molecules, with folded structures, including gluten which gives wheat bread its unique structure.

A special class of proteins that are able to promote the breakdown and construction of organic molecules. Enzymes play a key role in life.

The ash content stands for the amount of minerals in flour. Minerals are elements from the periodic system required by cells to function. Minerals are often required by enzymes to function properly.

Levain or pre ferment
The part of flour which is pre-fermented in a sourdough recipe using the sourdough starter. The levain is basically an activated starter that is allowed to grow extensively in a solution of water and fresh flour and is responsible for leaving and adding flavour to the bread.

Bulk fermentation
Initial stage of fermentation of the final dough.

Final Proof
Final fermentation phase of shaped breads, prior to baking.

Hydration, formation and development of  gluten without starting the main fermentation process. It improves (shotens) the following kneading process and gives the enzymes (amylases) a head start before a large number of microbes  (levain or commercial yeast) start consuming the fermentable sugars in the dough.