What went wrong?

One culture doing two jobs. The starter is the jar you keep alive and feed; it never all gets used, and it outlives every loaf. The levain is a small batch built from a spoonful of that jar a few hours before you mix, and all of it goes into the dough. Plenty of recipes say "starter" for both, which is where the confusion starts.

Building a levain rather than tipping in the jar means it goes into the dough at its peak, you can give it different flour than the jar gets, and a failed bake never costs you the culture. In this app the Starter tab is the jar; "Starter (levain)" in a formula is what goes in the dough, and the first step of a bake gives you the exact weights to build it from.

Baker's percentages are shares of the total flour, not of the dough. 20% starter with 500 g of flour means 100 g of levain.

You do not need to work it out. Set the pot or the flour weight and the percentages on the Calc tab or when starting a bake, and every number you have to weigh is listed underneath in grams.

Almost always an under-fermented bulk, or a levain that was not lively when it went in. The dough never built enough gas to open up.

Bulk until the dough has risen about 50% and feels alive — domed, jiggly, bubbles at the edges — rather than until the clock says so. If the levain took more than 6 hours to peak, feed the starter twice a day for a few days before trying again.

Two different faults look identical: cut too soon, or baked too little. Over-fermentation gives a third version, where the crumb is gummy and the loaf is also flat.

Bake to 205–210°F / 96–99°C internal, and leave it on a rack a full two hours before cutting. If it is flat as well as gummy, shorten the bulk next time.

Over-fermented dough, weak shaping, or more water than the flour can carry.

Cut the bulk by 30–45 minutes, shape tighter, and drop the hydration by five points. Supermarket plain flour will not hold 80% — that needs strong bread flour.

Over-proofed dough has no lift left. A cool oven or no steam will do it too.

Bake straight from the fridge, into a properly preheated Dutch oven — the pot wants 45 minutes at full temperature. Score one decisive cut about 1 cm deep at a shallow angle.

Gas trapped by loose shaping, or a skin that formed during the bench rest.

Pre-shape with real tension, keep the bench rest under 30 minutes, and cover the dough if the kitchen is dry.

The oven was not hot enough, or the lid stayed on too long.

Give it longer uncovered and take the colour further than feels right. A deep brown crust is where most of the flavour lives.

Long cold proofs, whole grain, and a starter that sits hungry all push acetic acid up.

Shorten the retard to 8–10 hours, use a younger levain at its peak, feed the starter more often, and keep the dough warmer rather than colder.

A young, frequently fed starter and a short, warm schedule make a mild loaf.

Retard 16–24 hours, add 10–20% whole rye or whole wheat, and let the levain go slightly past peak.

Usually too cold, or fed too rarely. Chlorinated water and bleached flour do not help.

Feed 1:1:1 twice a day and keep it at 77–82°F / 25–28°C — an oven with only the light on works. Swap a quarter of the flour for whole rye. Give it a week before deciding it has failed.

Hooch. It is alcohol, and it means the starter has eaten everything and is hungry.

Pour it off, feed at a bigger ratio such as 1:5:5, and feed more often or keep it cooler.

This is contamination, not fermentation. Healthy starter never grows fuzz and is never pink or orange.

Throw the whole jar out — do not scrape the top off and carry on, and do not bake with it. Wash everything and start again.

Volume alone lies, because it depends on the vessel. Read the surface and the feel.

Look for a 40–60% rise, a domed top, bubbles at the edge, and a wobble when you shake the bowl. The dough should feel full of air rather than heavy.

The poke test, which reads the gas structure rather than the clock.

Flour a fingertip and press 1 cm into the dough. Springs back fast: not ready. Springs back slowly and not all the way: bake it. Stays dented and sighs: over-proofed, bake it now and expect it flatter.