Why Your Sourdough Smells Like Nail Polish Remover

You pull the lid off your starter jar and get hit with a wave of something that smells like nail polish remover. It is sharp, chemical, and genuinely alarming. Your first instinct might be to dump it and start over. Do not do that. What you are smelling is completely normal, not dangerous, and very easy to fix.

What Is That Smell?

The smell is acetone (and related compounds like ethyl acetate), which is a byproduct of acetic acid fermentation. When your starter runs out of food, meaning all the flour has been consumed and there is nothing left to eat, the bacteria shift into a survival mode that produces more acetic acid and its volatile relatives. That is the sharp smell hitting your nose.

How to Fix It

The fix is straightforward: feed your starter more often, and it will stop producing that smell within 2 to 3 feedings.

Immediate fix: Discard all but about 25g of your starter. Feed it with 50g flour and 50g water (a 1:2:2 ratio). Let it ferment at room temperature. It should start bubbling within a few hours, and the acetone smell should be noticeably reduced.

Ongoing solution: If you keep your starter at room temperature, it needs to be fed at least once every 24 hours, ideally every 12 hours. If you cannot commit to that schedule, store it in the fridge and feed it once a week. The cold slows fermentation enough that it will not get desperately hungry between feedings.

When to Actually Worry

Acetone smell is normal and harmless. But there are smells that do signal a problem:

• Rotten garbage or vomit smell: Something genuinely wrong, likely contamination. Start fresh.
• No smell at all: Your starter might be dead or extremely dormant. Try a series of feedings and see if activity returns.

If it is pink, orange, or has fuzzy mold, discard it and start a new one. But that sharp, chemical, nail-polish-remover smell? That is just a hungry starter asking for dinner. Feed it and move on.