A starter that has stopped rising is cold, hungry or too acidic

What follows is an argument about sluggish sourdough starter, and about where the received version of it stops being true.

Temperature first

A starter is a population of yeast and bacteria whose working speed depends almost entirely on how warm they are. The same culture that doubles briskly in a warm kitchen can barely move in a cold one.

Seasonal changes catch people out, since a starter that was reliable in summer becomes sluggish in winter. Finding a consistently warm spot, or accepting a longer wait, resolves most of these cases immediately. Before concluding anything is wrong, check the temperature where the jar actually sits rather than the room average.

Acidity building up

Between feeds, the bacteria continue producing acid long after the yeast has run out of easy food. As acidity rises, yeast activity is suppressed, so the starter smells strong but stops lifting. A dark liquid on the surface indicates a starter that has been left well past its peak and is very hungry.

Feeding more often, or with a larger proportion of fresh flour and water, dilutes that acidity. Two or three generous feeds usually restore a culture that looked hopeless the day before.

Feeding ratios and what they change

A small feed leaves a high proportion of old, acidic starter and the culture peaks quickly then declines. A large feed dilutes the acid, gives the yeast more fresh food and produces a slower but stronger rise.

Once the crumb sets, discarding most of the starter before feeding is what makes a large feed practical without a growing jar. Whatever ratio you use, being consistent matters more than the specific numbers, since the culture adapts. Changing ratio, flour and temperature at once tells you nothing about which of them helped.

Flour and water

Wholemeal and rye flours carry more nutrients and more wild organisms, so they invigorate a slow starter. White flour alone is perfectly workable but gives a slower, milder culture that needs more patience. Very heavily chlorinated tap water can slow a starter, and letting the water stand or using filtered water is a common fix.

The dough tells you first: very hot water kills yeast outright, so anything that feels more than mildly warm to the hand is too hot.

Switching to a different flour for a few feeds is worth trying before concluding that a starter has failed.

What a genuinely dead starter looks like

Pink, orange or fuzzy growth of any colour means contamination rather than a sluggish culture, and it should be discarded. A truly dead starter shows no activity at all after several days of regular feeding in warm conditions. A strong acetone or nail varnish smell indicates extreme hunger rather than death, and it usually recovers.

The dough tells you first: a starter kept in the fridge for a long time is dormant rather than dead and often takes several feeds to wake. Follow national food safety guidance if you see any visible mould, and do not attempt to scrape it off and continue.

Flour absorbs water differently by brand and by season; hydration is a target, not a rule.

Judging readiness for baking

A starter ready to use has risen substantially, is domed or just past its peak, and smells pleasantly sour rather than sharp. Rising and falling before you use it means the peak has passed and the culture will be less energetic.

Marking the jar and noting how long the rise takes turns readiness into something you can predict. A starter used at its peak gives a faster, more reliable bulk fermentation than one used late. If the starter never doubles, no adjustment to the dough recipe will compensate for what the culture is not doing.

The takeaway

Warm it, feed it generously, give it fresh wholemeal, and only then start worrying about whether it survived.

Bake it badly once on purpose. The failure teaches more than the photograph.