A sharp alcoholic smell means the dough went past its useful point

There is a short answer about overfermented dough and a useful one, and they are not the same. What follows is the useful one.

What overfermentation does

As fermentation continues, yeast produce ethanol alongside carbon dioxide, and that alcohol accumulates when the dough is left too long. At the same time bacteria produce increasing quantities of lactic and acetic acid, which progressively degrade the gluten network.

The dough therefore becomes weaker exactly when it has the most gas to hold, which is why it collapses. The smell shifts from pleasantly yeasty and slightly sweet to sharply alcoholic, vinegary or reminiscent of nail varnish. That change in smell usually arrives before the visual signs are unambiguous, which makes it a useful early warning.

Reading the dough

An overfermented dough is slack, sticky and difficult to handle, and it spreads across the bench rather than holding a shape. Poking it leaves a dent that does not fill back at all, whereas a correctly proved dough fills slowly and incompletely.

The surface goes flat, blistered and slightly grey rather than domed and smooth. During shaping it tears rather than tightening, because the gluten no longer has the strength to build surface tension. Any one of these alone can be misleading, but three together are conclusive.

Why it happens

The most common cause is a warmer kitchen than the recipe assumed, since fermentation rate roughly doubles for a rise of eight to ten degrees. A three hour bulk written for a 21C kitchen can be finished in ninety minutes at 27C, and overproved by two hours.

Too much yeast or too much starter accelerates everything and narrows the window in which the dough is correct. A retard in a fridge running at 7C rather than 3C can ferment overnight far more than intended. Measuring the dough temperature and the fridge temperature removes almost all of this uncertainty.

Catching it early

Use an aliquot jar, a small sample of the dough in a straight-sided container, and mark 50 and 75 per cent on the outside. Ending bulk at a rise of 50 to 75 per cent for white sourdough leaves the dough with strength in reserve. Waiting for a full doubling is advice inherited from commercial yeast doughs, which acidify far less over the same period.

Check every thirty minutes rather than setting a single alarm for the recipe's stated time.

In a warm kitchen the window between ready and past it can be as short as twenty minutes.

Salvaging the dough

A mildly overproved dough can often be reshaped gently, given a short final prove and baked as a slightly flatter loaf. A badly overproved one will not hold any shape, and forcing it into a banneton wastes both the dough and your time. The better use is a flatbread, focaccia or pizza base, where a slack dough and a strong sour flavour are both acceptable.

Once the crumb sets, pressing it into an oiled tray, dimpling it and baking hot produces a genuinely good result rather than a consolation prize. Nothing about overfermented dough is unsafe; it is simply the wrong structure for a free-standing loaf.

Preventing a repeat

Record the final dough temperature after mixing and the actual time bulk took, then use those numbers rather than the recipe's. Reduce the starter or yeast quantity if you need a longer window for scheduling reasons. Move the dough somewhere cooler or use a water bath to hold a steady temperature rather than letting it drift upward.

For long retards, measure the fridge where the dough actually sits rather than trusting the dial on the front. Two bakes with recorded numbers will usually tell you more than a dozen without them.

The takeaway

Learn the smell, measure the rise in a jar, and turn the failures into focaccia.

Temperature and time are the same argument held at opposite ends.