Microbial Dynamics of Sourdough
A sourdough starter (levain) is a complex symbiotic culture of wild yeasts and Lactic Acid Bacteria (LAB). Maintaining this culture requires regular 'refreshment'—the process of discarding a portion of the culture and adding fresh flour and water. The ratio of this feeding dictates the acidity, leavening power, and peaking time of your starter.
Understanding Feeding Ratios
Feeding ratios are expressed as Starter : Flour : Water (e.g., 1:2:2).
- 1:1:1 (Maintenance): Keeps the culture active and stable. Peaking occurs rapidly (4-6 hours).
- 1:5:5 (High Ratio): Used to 'cleanse' a starter that has become too acidic or to time a peak for 12+ hours later. The lower 'inoculation' rate means the yeast has more food relative to its population, slowing down the cycle.
The Formula
The amount of food (flour and water) you provide is directly proportional to the amount of seed starter you retain.
Add Amount = Retained Starter * Ratio Part
The pH and Suffix of Sourdough
As the bacteria consume sugars, they produce lactic and acetic acids, lowering the pH of the starter. If you don't feed it regularly, the acidity will climb too high, eventually killing the yeast. Regular discarding is mandatory to prevent the starter from growing to an unmanageable volume and to prevent the buildup of 'hooch' (an alcoholic byproduct of hungry yeast).