What an Active Sourdough Starter Actually Looks Like
Almost every sourdough failure we hear about traces back to the same thing: the starter wasn't ready. Not dead, not contaminated, not the wrong flour — just used a few hours too early, on the assumption that bubbles mean ready.
Bubbles don't mean ready. Here's what does.
Active means predictable, not just bubbly
An active starter is one that does the same thing on the same schedule. Feed it, and it should roughly double within four to eight hours, hold at that peak for a while, then sink back down. If you can guess when it will peak tomorrow based on what it did today, it's active. If it's doing something different every day, it isn't yet — it's still establishing.
The single most useful thing you can do is put a rubber band around the jar at the level of the starter right after you feed it. Doubling is obvious then, and completely ambiguous without it.
The four signs, in order of usefulness
- It doubles on a predictable timeline. This is the real test and the only one that matters much.
- The top is domed, not flat or sunken. A dome means it's still rising; a crater means you've missed the peak.
- It smells yeasty and faintly tangy — like beer or plain yogurt. Sharp acetone or nail polish means it's hungry, not spoiled.
- The texture is webby and full of bubbles all the way through, not just a layer of foam sitting on top.
Skip the float test
You'll read that a spoonful of ready starter floats in water. Sometimes it does. A stiff starter can sink while being perfectly active, and a thin one can float on trapped gas well past its peak. It's a coin flip dressed up as a test — watch the jar instead.
If it isn't doubling
Nine times out of ten it's temperature or feeding, in that order. Wild yeast slows down badly below about 70°F, and a kitchen that feels fine to you can be well under that in winter. Find the warmest spot you have — on top of the fridge, inside the oven with just the light on — and give it a few days.
If temperature isn't it, the next thing to look at is what you're feeding it. Bleached flour and starter don't get along, and the flour you choose changes how fast the whole thing moves.
A starter you keep in the fridge is not a dead one
Refrigerating slows a starter almost to a stop, which is exactly the point if you bake once a week. Take it out, feed it, and give it two or three feeds at room temperature before you expect it to raise a loaf. The first feed after a cold spell is almost always sluggish, and that's normal.
One more thing: the flour you pour off before each feed isn't waste. It's the starting point for some of the best things in the kitchen.
We keep ours going year-round — it's the same starter behind every loaf and every pan of rolls we bake. If you'd rather skip the jar entirely, that's what the bake is for.