1:1:1 feeds with supermarket plain flour, kitchen is 19 to 20C through the winter, and it rises maybe 30% before it stalls and slowly sinks. It smells pleasantly yoghurty, no hooch, no funny colours, so I don't think it's ill. I'm after the specific thing that changed for you rather than another list of general tips.
Two smaller levers once the temperature is sorted. Swap 20% of each feed to whole rye or wholemeal — the bran carries minerals and enzyme activity that plain white flour has had removed, and it perks most sluggish starters up within a few feeds. On water: chlorine gasses off if you leave it standing, but chloramine, which many suppliers now use instead, doesn't, so if you're suspicious use filtered or bottled for a fortnight and compare rather than arguing about it. In my experience it's rarely the water and almost always the thermometer.
I timed mine to make the same point with numbers. Same starter, same feed: peak at about 4.5 hours sitting at 26C, and roughly 12 hours at 20C. The rule of thumb bakers use is that fermentation roughly halves in speed for every eight to ten degrees you drop, and that matches what my jar does. So if you feed at 8am and check at 2pm in a 19C kitchen, you are looking at a starter that is nowhere near its peak and concluding it's broken. Mark the jar with a rubber band and check it at hour ten and hour fourteen before deciding anything.
I'd also retire 'doubling' as your target. Apparent rise depends on jar diameter, hydration and how much you stirred the air out, so a wide jar makes a healthy starter look lazy. Use an aliquot — a tablespoon of the mixed dough in a small straight-sided container — or just accept a reliable 50 to 60% rise, which bakes perfectly good bread. I've had starters that never doubled in their lives and made better loaves than ones that tripled.
The jar width thing caught me out for months. Moved from a wide preserving jar to a tall narrow one, changed nothing else, and suddenly it was 'doubling'.
Warmer spot, twice the wholegrain, and judge it at its peak rather than at a convenient hour. Six weeks old and smelling good means it's fine.
@sourdough_stella · 3mo ago · 2 replies
Temperature, and it isn't close. At 19C a starter is alive but working at a fraction of the speed, and by the time it would have peaked you've already fed it again and reset the clock. Mine did exactly your 30%-and-stall in a cold flat and doubled reliably the week I started putting the jar in the oven with just the light on, which sits around 25 to 27C in my oven — check yours with a thermometer because some run much hotter. Nothing else changed: same flour, same ratio, same jar.
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@batch_bea · 3mo ago
Cheaper version if your oven light is LED and produces no heat: a cool bag with a jar of warm water in it, swapped morning and evening. Held mine at about 25C all winter for the price of nothing.
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