A sourdough starter is a living mixture of flour and water that contains wild yeast and lactic acid bacteria, used to ferment and raise sourdough bread.
The quick answer
Think of a starter as your reusable raising culture. You keep a small amount, feed it with fresh flour and water, then use part of it when it is active. With regular care, the same culture can be maintained for years.
What is living inside a starter?
Flour naturally carries microorganisms, and more are present in the surrounding environment. When flour and water are mixed and refreshed repeatedly, conditions favour a community of yeasts and acid-producing bacteria that can live together.
The yeasts consume available sugars and release carbon dioxide. This gas helps bread rise. Lactic acid bacteria produce acids and flavour compounds, helping create the aroma and character associated with sourdough. The acidity also helps the culture remain stable when it is cared for correctly.
You do not need to identify individual strains to bake good bread. What matters at home is whether the culture rises reliably after feeding, smells clean and fermented, and reaches its active stage within a reasonably predictable window.
Starter, levain and discard: what is the difference?
- Starter: the culture you maintain from one bake to the next.
- Levain: a portion of starter built for a particular recipe. It may use a different flour, hydration or feeding ratio.
- Discard: starter removed during feeding. It may be unfed or past peak and can be used in suitable discard recipes if it is healthy.
The words starter and levain are sometimes used interchangeably. The practical distinction is that your starter is the culture you keep, while a levain is usually a recipe-specific build that you intend to use.
Why does a starter need feeding?
A feed supplies fresh flour and water. The microorganisms use nutrients from the flour, multiply and produce gas and acids. As that food is used up, activity slows and the starter eventually falls. Feeding begins a new cycle.
A common feeding ratio is written as 1:1:1—one part starter, one part flour and one part water by weight. For example, 25 g starter, 25 g flour and 25 g water. A larger feed such as 1:2:2 gives the culture more fresh food and normally takes longer to peak.
Common mistake: measuring feeds by volume
A tablespoon of water and a tablespoon of flour do not weigh the same. Use digital scales and calculate feeding ratios by weight. This makes the starter’s hydration and behaviour much more repeatable.
What does hydration mean in a starter?
Hydration describes water as a percentage of flour by weight. A starter containing equal weights of flour and water is at 100% hydration. It should be thick and spoonable when freshly mixed, although different flours absorb water differently.
Some bakers keep a stiff starter with less water; others maintain a liquid culture. Neither is automatically better. A 100% hydration starter is a useful standard for beginners because the maths is simple and many recipes are written for it.
How do you know when a starter is active?
- It has risen noticeably—often close to double, depending on the flour and consistency.
- Bubbles are visible throughout the jar, not only on the surface.
- The top is rounded or domed before the starter reaches its peak.
- The aroma is pleasantly fermented, tangy or yeasty rather than rotten.
- It repeats this pattern predictably after feeding.
Watch the rise, not the float
The float test is not a dependable readiness test. Hydration, flour and the way a sample is handled can make an active starter sink or a weak one float. Rise, bubbles, shape, aroma and repeatable timing give you better evidence.
Where should you keep a starter?
If you bake frequently, keep the starter at room temperature and feed it often enough that it does not remain hungry for long periods. If you bake less often, keep it in the fridge between bakes. Refrigeration slows fermentation; it does not stop it completely.
Use a clean food-safe jar with enough space for the starter to expand. Rest the lid on or fasten it loosely according to the jar design. You want to prevent contamination without allowing pressure to build in a tightly sealed container.
A simple observation routine
- Mark the starter’s level immediately after feeding.
- Note the room temperature and feeding ratio.
- Check when it reaches its highest point.
- Repeat the same feed for several cycles before changing variables.
This small record tells you far more than copying someone else’s feeding timetable.
When is a starter unsafe?
A hungry starter may smell strongly acidic or acetone-like, and it may develop a greyish liquid commonly called hooch. Those signs usually call for a refresh. They are different from obvious contamination.
Discard the culture if you see fuzzy mould, pink or orange colouring, or detect a rotten smell. Do not taste it or scrape away the affected area. Clean the jar and tools thoroughly before starting again with a sound culture.
Sourdough starter questions beginners often ask
Is a starter the same as yeast?
It contains yeasts, but it is not the same as a packet of baker’s yeast. A starter is a mixed culture of yeasts and bacteria maintained in flour and water.
How old must a starter be before baking?
Age alone is not the useful test. A starter is ready when it rises strongly and predictably after feeding. A new homemade starter may take several weeks to become dependable, while an established culture can be used once it has recovered from transport and is feeding well.
Do I have to discard starter every day?
No. Discarding controls the total quantity before feeding. Once your culture is established, you can keep a small starter, refrigerate it between bakes and plan feeds to minimise waste.
Which flour should I use?
Unbleached bread flour is simple and consistent. Wholemeal and rye flour often produce lively fermentation because they contain more of the grain, but they also change texture and water absorption. Consistency matters more than constantly changing flour.
Can a starter really last for years?
Yes. The culture continues through repeated refreshments rather than remaining as the same untouched flour and water. Good hygiene, regular feeding and sensible storage allow it to be maintained indefinitely.
Start with an established heritage culture
Our starter kits include a living culture and clear guidance for feeding, storing and baking. They remove the uncertain early stage of creating a culture from scratch.
Continue learning
Now follow the first week step by step: feeding, observing and building enough strength for your first loaf.
A good way to learn
Focus on repeatability before optimisation. Use one straightforward recipe, keep notes on temperature and timings, and change only one thing on the next bake. You will learn faster from three comparable loaves than from three completely different methods.
