From flour & water
to a living thing
you'll feed for years.

Wild yeast multiplies fastest between 75–80°F. Below 70°F, growth slows dramatically. Below 65°F, it can stall entirely in a brand-new starter that doesn't yet have a thriving population.

On top of the fridge, near a south-facing window (out of direct sun), or inside the oven with just the interior light on (creates a stable 78–82°F box). A heating pad on its lowest setting under a tea towel works too.

The yeast and bacteria have metabolized all the available carbohydrates. With nothing left to eat, they produce acetone (the same compound found in nail polish remover) as a byproduct.

Discard down to 25g and feed 1:5:5 (25g starter + 125g flour + 125g water). The extra-large feeding gives the yeast plenty to work with and helps mellow the acidity.

Mold spores enter the jar and find a home — sometimes from a wooden spoon that wasn't rinsed clean, sometimes from a jar that had old crust on the sides feeding spores.

Compost the starter, wash the jar in hot soapy water, and start over. Skimming or stirring will not work — mold mycelium has already penetrated below what you can see.

Most common cause. The starter ate everything, finished producing CO2, and is now sitting in its own alcoholic exhaust.

For tangier bread, stir the hooch (which contains organic acids) back into the starter, then feed normally. Most bakers do this.

The float test is most accurate when starter is at peak — domed top, just before it falls. A spoonful taken from a starter that has already fallen has released most of its gas and will sink even though the culture is healthy.

Use a rubber band on the jar to mark where the starter sat after feeding. Test the moment it's tripled and domed — that's the best-case scenario for a float test.

At 78–82°F, a 1:1:1 or 1:2:2 starter can finish in three hours. You're catching the rocket on the way down.

More fresh food per unit of starter extends the time-to-peak. 1:5:5 typically peaks at 6–8 hours in a warm kitchen; 1:10:10 at 10–12. Both give you a longer window.

Same flour, same ratio, same starter — but a 60–65°F kitchen ferments at a fraction of the speed of a 75–80°F one. This is the most common cause.

On top of the fridge (typically 75–78°F from the compressor's waste heat), near a heating vent, on the back corner of the stove if you bake daily, or inside the oven with just the interior light on (78–82°F).

Common in starters under 3 weeks old. Bacteria establish faster than yeast — you'll smell the bacteria long before you see the yeast.

Bigger feedings select for the yeast population (yeast outcompetes bacteria when food is abundant). Twice daily prevents the starter from over-acidifying between feedings.