Why is there liquid on top of my sourdough starter?

A starter eats the available flour, produces alcohol and acid, and when the food runs out the alcohol and water separate to the surface. That is hooch. Its appearance is a straightforward hunger signal and a starter that produces it every day is being underfed for how warm it is being kept. What matters is telling hooch from the two things that genuinely mean throwing the jar out: fuzzy coloured mould, and pink or orange streaks.

Safety

Step by step

1. Look at it before doing anything.Hooch is a clear-to-grey or brownish liquid layer sitting on top, sometimes with a strong smell of nail varnish or spirits. It is uniform, not fuzzy, and not coloured pink or orange.
2. Rule out mould and pink streaking.Anything raised, fuzzy or velvety, in any colour, means discard. Pink or orange streaks mean discard. A darkened crust where the starter has dried on the jar wall is neither of those and is harmless.
3. Decide whether to pour it off or stir it in.Pouring it off removes some acidity and gives a milder starter and milder bread. Stirring it in keeps the acid and gives a sharper flavour. Neither is wrong — see `control-sourdough-sourness`.
4. Read the colour as a hunger gauge.Clear or pale grey means it has been hungry for a day or so. Dark brown or almost black means considerably longer, and the starter may need two or three feeds before it is baking-strength again.
5. Feed at a bigger ratio, not just more often.If a starter is producing hooch daily at room temperature, discard most of it and feed 1 part starter to 5 or 10 parts each of flour and water. More food per unit of culture is what stretches the interval between feeds.
6. Move it somewhere cooler if that suits you better.A fridge starter fed once a week is normal and will produce hooch between feeds. That is fine for weekly baking; feed it twice at room temperature before a bake to bring it back to strength.
7. Give it two or three feeds before baking with it.A starter recovering from a long hungry period will not double reliably on the first feed. Bake when it doubles within four to six hours of feeding, not before.

Tips

• Hooch is more common in liquid starters than stiff ones, simply because there is more free water to separate out.
• A starter kept in the fridge and fed weekly is the low-effort option and hooch between feeds is expected. It is not neglect if you feed it up before baking.
• Discard is not waste. Sourdough discard makes crumpets, pancakes, crackers and flatbreads without needing any rise at all.
• A wide jar with a loose lid is better than a sealed one. Sourdough produces gas and a sealed jar can build pressure.

Common mistakes

• Throwing the starter away at the first sight of hooch — It is the most normal thing a starter does. Feeding it fixes it in a day.
• Scraping mould off and carrying on — Mould in a wet culture is not confined to the visible patch. This is the one situation where the whole jar goes.

If it doesn't work