Lactic acid fermentation
Also searched as: sourdough, fermentation, souring, yoghurt
In short: Lactic acid bacteria turn sugar into acid. That gives sourdough and yoghurt their flavour and makes them keep longer.
Like a shared household: bacteria take care of acid and flavour, the wild yeasts in sourdough take care of the gas.
Simplified model
What happens
In sourdough, lactic acid bacteria and wild yeasts live together. The bacteria make lactic and acetic acid, the yeasts make gas. The acid adds flavour, strengthens the structure of rye dough and keeps bread fresh longer.
Why it matters
Explains why sourdough bread tastes different and stays fresh longer, and why rye can hardly be baked without acid.
Rules of thumb
- Warmer ferments milder, cooler more sour (as a guide).
- An active sourdough doubles within a few hours after feeding.
Levers
In practice
Bread
Rye bread needs acid so the dough can be baked and the crumb does not turn sticky.
Milk and cheese
Yoghurt forms when lactic acid bacteria sour milk and the protein thickens.
- Harold McGee: On Food and Cooking (2004), Kapitel Brot, Getreide