Knowledge Base

Sourdough Starter

Levain

Grain ferment · Traditional · peer-reviewed

A stable culture of wild yeast and lactic bacteria kept alive on flour and water — the leavening and the sour in every loaf of real sourdough.

Moderate to make
5–10 days ferment
wild-yeast, lactic-acid, leavening supplied

Ingredients

  • Wholemeal or rye flour (to start)50 g/day
  • Water, non-chlorinated50 g/day

How to make it

  1. Step 1

    Day 1: mix 50 g wholemeal flour with 50 g water in a jar. Cover loosely.

  2. Step 2

    Keep at 22–26 °C. Warmth speeds establishment.

  3. Step 3

    Days 2–5: each day discard most of it and feed with fresh 50 g flour + 50 g water.

  4. Step 4

    Watch for it to double between feeds and smell tangy-yeasty, not just sour.

  5. Step 5

    Once it reliably doubles in 4–8 h it's mature. Refrigerate and feed weekly, or keep out and feed daily.

What it is

A sourdough starter (levain) is a living culture of wild yeast and lactic-acid bacteria carried in a paste of flour and water. Refreshing it with fresh flour keeps the microbes fed; a spoonful leavens bread and gives it the characteristic sour tang, entirely without commercial baker's yeast.

The science

Mature sourdough is a remarkably stable, self-selecting consortium. It is dominated by lactic-acid bacteria — classically Fructilactobacillus sanfranciscensis — together with sourdough yeasts such as Kazachstania humilis or Saccharomyces cerevisiae, typically at a ratio around 100:1 LAB to yeast (De Vuyst et al., 2014). The yeast provides most of the CO₂ that raises the dough; the bacteria produce lactic and acetic acid for flavour and keeping-quality.

Acidification also switches on cereal and microbial enzymes that break down starch, protein and phytate, which improves texture, flavour and mineral availability in the finished bread (Gänzle, 2014). The balance of the two acids — and so the taste — shifts with temperature and hydration (De Vuyst & Neysens, 2005).

Signs it worked / troubleshooting

  • ✅ Good: reliably doubles in 4–8 h, domed and bubbly, pleasant yeasty-sour smell.
  • ⚠️ Grey liquid on top ("hooch") = hungry starter → pour off and feed more often.
  • 🚫 Pink/orange streaks or fuzzy mould = contamination → discard and start over.

How to store

Keep it on the counter and feed daily, or refrigerate a mature starter and feed weekly. It can be dried to a powder for long-term backup and revived later.

References

  • De Vuyst L, Van Kerrebroeck S, Harth H, Huys G, Daniel HM, Weckx S (2014). Microbial ecology of sourdough fermentations: diverse or uniform? Food Microbiology 37:11–29. doi:10.1016/j.fm.2013.06.002
  • Gänzle MG (2014). Enzymatic and bacterial conversions during sourdough fermentation. Food Microbiology 37:2–10. doi:10.1016/j.fm.2013.04.007
  • De Vuyst L, Neysens P (2005). The sourdough microflora: biodiversity and metabolic interactions. Trends in Food Science & Technology 16(1–3):43–56. doi:10.1016/j.tifs.2004.02.012

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