When it goes wrong · Boil
The pot boiled over.
Can you save it?
Reviewed for this symptom
Lower the heat and add a splash of cold water or lay a wooden spoon across the pot; the foam collapses at once. Wipe the hob before the sugar and starch bake on.
How to confirm the diagnosis
Observable cues, not inferred user state
- A foaming head rising in seconds
- The pot is small for the quantity
- The heat stayed at full after the boil
Not this?
What actually happened
Only this symptom
Starch and protein foam stabilising the bubbles. A wooden spoon across the top or a splash of cold water knocks it down; so does simply lowering the heat, since it was already as hot as it can get.
The full mechanism
Shared by every boil failure
At normal pressure water tops out at 100°C however hard it boils, so more heat under a boiling pot makes it boil faster, not hotter. What a rolling boil provides that a simmer does not is movement: it keeps pasta separated so it cannot glue itself together, it circulates heat so a large pot has no cold spots, and it supplies the energy that fully gelatinises starch in a thickening slurry. Salting pasta water is not about raising the boiling point — the effect at kitchen concentrations is a fraction of a degree and irrelevant. It is the only opportunity to season the pasta itself, and the dissolved starch that comes off into that water is a genuinely useful emulsifier. Less water gives a more concentrated starch solution, which is why the traditional advice to use a huge pot is worth ignoring for most sauces.
The full Boil lesson — how to tell, where to practise it, what it carries to.
Next time
Prevent this specific failure
A bigger pot with the water lower than two-thirds, the heat turned down once it boils, and a spoon across the rim.
What right looks like
Shared by every boil failure
- The whole surface is in motion and bubbles rise everywhere, not just from a few points.
- Adding food drops it out of the boil; how fast it returns tells you whether the pot is big enough.
- Pasta water should taste seasoned, not like the sea — around a tablespoon of salt per litre.
- Starch-thickened liquids turn from opaque and matte to glossy at the moment they reach a boil, which is the endpoint.