The water you were about to throw away

Why a sauce slides off

Oil and water do not mix, and a sauce that has separated is not a sauce — it is a slick sitting on top of a puddle. Something has to stand between them and hold both. Starch does that: its long molecules tangle through the water and give the fat droplets something to catch on, so the two stay suspended in each other instead of parting the moment you stop stirring.

Worth remembering A sauce that pools at the bottom of the pan is missing a binder, not more fat.

Pasta water is not water

The cloudiness in a pot of cooked pasta is starch the pasta shed. A ladle of it, tossed hard in the pan with the sauce and a little fat, turns a thin sauce glossy and makes it cling. This is why Italian recipes finish the pasta in the pan for the last minute instead of pouring sauce over a drained bowl — and why the single most common ruin of a good sauce is tipping that water down the sink.

Worth remembering Save a mug of the water before you drain. Every time.

Every starch needs to get wet first

Starch grains have to absorb water one at a time before heat can swell them. Thrown dry into something hot, the outsides gel instantly and seal the dry middles in — those are the lumps, and they are dry flour inside forever. A slurry mixes it with cold liquid first; a roux coats it in fat so the grains cannot touch each other. Two routes to the same requirement.

1. Runs off
2. Coats
3. Lumpy

Worth remembering Lumps are not too much starch. They are starch that never got wet.

Or use no starch at all

Boiling a sauce down does the same job by the other end: take water out and what is left is concentrated enough to coat on its own. It costs time and it costs volume, and it concentrates the salt along with everything else — which is why a sauce you intend to reduce is one you season at the end, never at the start.

Worth remembering Thicken by adding, or thicken by removing. Salt only once you have decided which.