Sourdough.
A spoonful of starter fed 1 : 5 : 5 in the evening peaks by morning; fed 1 : 1 : 1, it peaks by mid-afternoon. The microbes need time to fill the new flour.
Before commercial yeast, all bread was leavened by a culture kept from the last batch: a sourdough starter (老面 in Chinese steamed-bread making, XXVI.3). Flour and water left at room temperature are colonised by the wild yeasts and lactic acid bacteria already on the grain and in the kitchen (XIV.1); fed fresh flour and water every day or two, the community stabilises within a week or two into a starter that rises predictably. The yeasts make carbon dioxide; the bacteria, far more numerous, make lactic and acetic acids, which lower the pH to about 3.5–4, giving flavour, keeping the dough safe from spoilers (XIV.3), slowing staling and changing the gluten.
Feeding is dilution: one part starter with five parts each of flour and water dilutes the microbes elevenfold, and the starter "peaks" — domed, bubbly, at its highest — when they have multiplied back. That takes longer for bigger feeds and cooler rooms, which is how bakers time a starter to be ready when they want it. Cooler, stiffer starters lean towards acetic acid and a sharper sourness; warmer, wetter ones towards lactic acid and a milder, yoghurt-like tang. The workshop feeds a starter.
Below: the hours for a starter fed at the ratio you choose to peak at the temperature you choose — the doublings needed to recover from the dilution, times the doubling time of lactic acid bacteria (microbe bench, the course's teaching parameters from XIV.3).
- Explain what lives in a starter.
- Time a feeding to peak when needed.
- Control sourness by temperature and hydration.
- Keep a starter healthy.
Dilute, wait, use at the peak
With these teaching parameters a starter fed 1 : 1 : 1 at 24 °C peaks in about 7 hours and one fed 1 : 5 : 5 in about 15; at 20 °C the 1 : 5 : 5 feed takes about 20 hours and 1 : 10 : 10 about 26 — a full day. Real starters are often quicker, their yeasts and bacteria tuned by months of feeding, but the pattern holds: bigger feed or cooler room, later peak. Use the starter at or just before its peak, when it is most active, or the dough will rise slowly and taste sharp.
Keeping a starter: feed it once or twice a day at room temperature, or keep it in the fridge and feed it weekly, with one or two room-temperature feeds before baking; discard (or cook with — pancakes, crackers) what you do not keep. A sourdough bread typically uses 15–25 % starter of the flour weight, a long bulk fermentation (4–8 hours) and often a cold retard (XXIV.6). Grey liquid on top (hooch) means hunger, not spoilage; pink, orange or fuzzy growth means start again (XIV.10).
Feed your starter (or start one) at 1 : 2 : 2 and 1 : 5 : 5 in two marked jars at the same time, and note when each reaches its peak.
Terms
- Starter (levain)
- A culture of wild yeasts and lactic acid bacteria in flour and water.
- Feeding ratio
- Parts of flour and water added per part of starter.
- Peak
- The starter at its highest, most active point after a feed.
- 老面
- A Chinese sourdough kept from batch to batch for steamed bread.
Sources
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.