Sourdough Starter
A sourdough starter is a living culture of wild yeast and lactic acid bacteria kept in a mix of flour and water. Bakers feed it regularly and use a portion of it to leaven bread, giving sourdough its rise, its chewy texture, and its tangy flavour.
What lives in a starter
A healthy starter is a small ecosystem:
- Wild yeasts, such as Saccharomyces cerevisiae and Kazachstania humilis, produce carbon dioxide that raises the dough, plus some alcohol.
- Lactic acid bacteria, such as Fructilactobacillus sanfranciscensis and Lactiplantibacillus plantarum, outnumber the yeasts many times over. They make lactic and acetic acids, which give the sour taste and keep spoilage microbes out.
The acids drop the starter's pH to around 3.5–4, too acidic for most harmful microbes. That's why a mature starter is so resilient.
Starting one from scratch
Wild microbes are already on flour. You only need to give them food, water, and time.
- Mix equal weights of whole grain flour and water, for example 50 g each.
- Every 24 hours, discard all but about 50 g and feed with 50 g flour and 50 g water.
- Keep it at 24–27 °C (75–80 °F) if you can.
Expect a burst of bubbles around day 2–3, then a quiet spell. Keep going. By days 7–14, it should rise and fall on a predictable schedule.
Chef Fizz says: The day-four slump is real. Nearly every starter goes quiet before it gets serious. Don't quit now.
Feeding ratios
Ratios are written as starter : flour : water by weight.
| Ratio | Time to peak at ~24 °C (75 °F) | Use when |
|---|---|---|
| 1:1:1 | 4–6 hours | Baking the same day |
| 1:2:2 | 6–8 hours | Feeding morning, mixing dough evening |
| 1:5:5 | 10–12 hours | Overnight, or in a hot kitchen |
A higher ratio gives the microbes more food, so it takes longer to peak and tastes milder.
Signs of a healthy starter
- Doubles or more after feeding.
- Domed top with bubbles throughout.
- Smells tangy, yeasty, and a bit like yogurt or beer.
A slightly flat, very sour or nail-polish smell means it's hungry. Feed it more often or at a higher ratio.
When to toss it
Pink or orange streaks, or fuzzy mould in any colour, mean contamination. Discard it and start fresh.
Starter vs levain
A levain is a portion of starter built up specifically for one bake, often with a recipe's flour and timing. The starter is the mother culture you keep going. A mature starter at 100% hydration adds equal parts flour and water to a recipe, which matters when you calculate dough hydration.
Questions
How long does it take to make a sourdough starter?
Usually 7–14 days of daily feedings before it rises reliably. Cool kitchens and certain flours can stretch that to three weeks.
What is the liquid on top of my starter?
That greyish liquid is called hooch, a mix of alcohol and water produced when the starter is hungry. Pour it off or stir it in, then feed the starter.
How do I know my starter is ready to bake with?
It should reliably double in volume within 4–8 hours of feeding at about 24 °C (75 °F), smell pleasantly sour and yeasty, and have a domed, bubbly top. That peak is the best time to use it.
Why did my starter bubble on day 2 then stop?
Early bubbles usually come from bacteria that don't survive as the culture turns acidic. The quiet phase that follows is normal; keep feeding and the yeast population will take over.
Can you keep a sourdough starter in the fridge?
Yes. A mature starter can live in the fridge and be fed about once a week. Take it out and give it one or two feedings at room temperature before baking.