Starter / Discard

A sourdough starter is a living, self-sustaining ecosystem of wild yeast (principally Saccharomyces cerevisiae and Kazachstania humilis, formerly Candida milleri) and lactic acid bacteria (primarily Lactobacillus species, especially L. sanfranciscensis — now reclassified as Fructilactobacillus sanfranciscensis). The two organism types coexist symbiotically: wild yeasts produce carbon dioxide for leavening and ethanol; bacteria produce lactic and acetic acids that flavor the bread, lower pH to inhibit spoilage organisms, and make gluten more extensible via protease activity. Starters are maintained by regular feeding (refreshment): a portion of the existing culture is combined with fresh flour and water, and the remainder — the discard — is removed. The discard is not waste; it is mature, tangy, and teeming with organisms useful for flavoring non-yeasted baked goods, pancakes, crackers, pasta, and quick breads. A well-maintained starter stored at room temperature needs feeding once or twice daily; refrigerated starters can go 5–7 days between feedings, though their leavening activity diminishes proportionally and they need one or two room-temperature refreshments before building a levain. Hydration is flexible: 100% (equal weights flour and water by mass) produces a pourable starter that many bakers find easiest to read for activity signs (bubbles, rise, dome, fall); stiffer 50–70% starters tend to express more acetic acid and are traditional in some French, Italian, and German bakehouse cultures. A healthy starter smells yeasty, slightly acidic, and mildly alcoholic; an over-fermented one smells strongly of acetone or nail polish remover, signaling the yeast population has starved and bacterial byproducts dominate.

“She kept her starter in a 500 ml jar on the counter, discarding half and feeding it with 50 g flour and 50 g water each morning; the discard went straight into overnight waffle batter.”

• glossaryLevain
• glossaryBiga
• ConceptWild Fermentation

1. 1.Tartine Bread — Chad Robertson (Chronicle Books, 2010)
2. 2.The Sourdough School — Vanessa Kimbell (Kyle Books, 2018)
3. 3.Modernist Bread — Nathan Myhrvold & Francisco Migoya (The Cooking Lab, 2017)
4. 4.Microbiology and Technology of Fermented Foods — Robert W. Hutkins (Blackwell, 2006)

Confidence: high