How Sourdough Feeding Ratios Control Fermentation Kinetics
A sourdough starter is a living symbiotic ecosystem of wild yeasts (primarily Kazachstania exigua and Candida humilis) and lactic acid bacteria (predominantly Fructilactobacillus sanfranciscensis). How much you feed them relative to their existing biomass determines how rapidly they consume available maltose and ferment.
Feeding ratios are written in the format Starter : Flour : Water. Consider the difference between a 1:1:1 feeding and a 1:5:5 feeding:
- 1:1:1 Ratio: Small buffet. With equal parts starter and fresh food, the microbial population finishes consuming available sugars rapidly, reaching peak rise in roughly 4 to 6 hours at 24°C (75°F). This ratio is perfect when you need ripe levain quickly for same-day baking.
- 1:5:5 Ratio: Feast. Keeping 20g of starter and adding 100g of flour and 100g of water (producing a 220g new culture) dilutes the bacterial acidity and requires 10 to 14 hours to reach peak rise at ambient temperature. This is the gold standard for overnight levain builds or weekly refrigerator maintenance.
The Critical Importance of Temperature
Fermentation rate doubles with roughly every 10°F (5.5°C) increase in dough temperature. In winter kitchens (18°C – 20°C / 65°F – 68°F), a 1:1:1 starter might require 8 to 10 hours to double in volume. In mid-summer (27°C / 80°F), that same 1:1:1 feed will peak and begin collapsing into alcohol (hooch) in under 3.5 hours.
To manage a warm summer kitchen, switch your maintenance ratio to 1:3:3 or 1:5:5. The higher proportion of fresh flour and water buffers acid accumulation, keeping the gluten matrix strong and preventing the starter from turning overly sour and runny.
Why You Must Discard Starter
New bakers often feel guilty about discarding starter. However, discarding 40g of starter from a 60g jar when retaining 20g is not waste—it is the biological necessity of refreshing the colony. Because sourdough bacteria produce acetic and lactic acids as byproducts, failing to discard allows acid to build to toxic levels, eventually killing the yeast and producing an unpleasant acetone odor.