7 Signs Your Sourdough Starter Is Ready to Bake - Don't Miss #4

The foundational sign. Doubled means the top of the starter is at 2× the level it was right after feeding (the rubber band mark). Not 50% rise, not almost doubled - actually doubled. A starter that doubles in 4-8h at 22-24°C has the activity level needed to leaven bread reliably. If it doubles in 12-16h at that temperature, it works but is slower than optimal; a stronger feed (1:5:5) the day before a bake will bring it to peak faster.

At peak, the surface of a well-fed starter bulges upward in a dome shape - it's full of CO2 bubbles that haven't yet collapsed. A flat surface means it hasn't peaked yet or peaked and fell slightly. A sunken, liquid-looking surface means it's past peak and on its way down. Time your bake for when the dome is at its highest.

Look at the jar from the side. At peak, you'll see a network of irregular, stretchy-looking bubbles clinging to the glass - the gluten web the yeast CO2 is trapped in. Fine bubbles in an even grid mean low-gluten flour (rye or high whole-grain). Irregular, open, stretchy-looking bubbles mean good gluten development and a well-leavened starter. No bubbles at the sides, even at 'peak height', means under-developed fermentation.

This is the most important sign of readiness and the one that gets least attention. A single doubling tells you today's starter is active. Consistent doubling at the same time window, across five or more consecutive feeds at a stable temperature, tells you the colony is established and reliable. The difference: a starter that peaked once at 7h might peak at 11h next time and 5h the time after. A starter that reliably peaks at 7-8h for five days in a row will leaven your bread predictably every single bake. Consistency is the metric to optimise for, not a single impressive rise.

At peak, a healthy starter smells of lactic acid - mildly tangy, faintly dairy, alive. Not sharp vinegar (that's past peak), not acetone (that's hungry), not alcohol (that's starved). The smell is part of the readiness check. If the starter looks right but smells wrong, trust the smell - it's ahead of the visual.

At or near peak, just watching the jar for a minute you should see occasional small bubbles rising through the mass. This is CO2 being released by actively fermenting yeast. If the starter is completely still - no movement visible over a few minutes of observation - it's either pre-activity (just fed, too early) or post-peak (past its high point). Peak is when you can see the starter breathing.

The famous test: drop a small teaspoon of starter in a glass of water. If it floats, the starter is aerated enough for bread. If it sinks, it may not be ready. The caveat: false negatives are common - especially with rye. Rye contains compounds called pentosans that prevent it from forming a proper gluten network, so the CO2 produced during fermentation escapes instead of being trapped. Even a highly active rye starter won't pass the float test, not because it's unready but because rye physically can't hold the gas that makes it float. A starter fed with rye or high whole-grain flour reliably doubles but will sink every time - and still bakes excellent bread. Use the float test as one supportive signal alongside the other six, not as the sole readiness criterion. If signs 1-6 are all present, you don't need the float test.

If you're going to use the float test as a supporting signal, do it properly - most false negatives are method errors, not an unready starter. The steps: take a clear glass of room-temperature water. Do not stir the starter first - stirring or tapping pops the trapped CO2, and a degassed sample sinks even when it's at peak and perfectly ready (this is the number-one mistake). Gently scoop about half a teaspoon from the top surface, where the gas sits, not dragged from the dense bottom. Drop the blob in; don't push it under. Test it at peak, not hours later when the gas has already escaped.

And read it as a one-way test: floating does not guarantee readiness, and sinking does not prove the opposite. King Arthur's own experiments had dough risen only 30 minutes - nowhere near ready - float happily, while at-peak rye starters sank. So treat a float as 'probably aerated' and a sink as 'check the other six signs before you worry'. If signs 1 through 6 are present, you don't need this test at all.

There are really two readiness questions, and they get mixed up. For a brand-new starter the question is 'is it mature enough to bake at all?' - and the honest bar is high: it needs to be at least about two weeks old and double reliably on three feeds in a row before its first loaf. Baking earlier gives you a flat, dense disappointment and a wrongly-blamed recipe. For an established starter the question is per-bake: 'is it ripe right now?' That's the peak-timing judgment the seven signs above are for. If you've just started a starter from scratch, you're answering the first question; if you bake every week, you're answering the second.

Peak time depends on feed ratio and temperature, so learn your jar's number rather than a universal one. As rough anchors: a 1:1:1 feed at room temperature (~22-24°C) peaks in about 3-6 hours; a bigger 1:5:5 feed takes 8-12 hours; warmer kitchens shave 30-60 minutes off, and a cool room or huge feed can stretch past 12 hours. Mark the jar at feeding, note when it crests, and after a few feeds you'll know exactly when to mix.

If it simply isn't there yet, don't force it. A young or sluggish starter wants warmth (~25-27°C), a feed or two of whole rye to boost activity, and a day or two more of patience. A starter that has already collapsed past peak isn't broken - just feed it and wait for the next rise. And if it sank the float test but meets the other signs, bake anyway. The fastest way to stop guessing is to log the peak time, temperature, and feed ratio every day; the consistent number is your green light.

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