Rescues · TO SIMMER
Stock is cloudy and greasy.
Why it happens
Boiled. Agitation emulsifies fat into the liquid and breaks up the protein scum that would otherwise be skimmed off.
Recovering it
A cloudy stock cannot be made clear by straining alone, though a slow strain through cloth helps and chilling lets the fat lift off in a solid cap. Broken sauces come back by whisking into fresh emulsifier off the heat. A thin starch sauce is easily fixed — bring it to a proper boil, which is the step that was skipped. Fish that has broken up is a texture loss, not a flavour loss; it becomes a soup or a fishcake.
The mechanism
Water boils at 100°C and cannot get hotter at normal pressure, so a rolling boil is not hotter than a simmer by more than a few degrees — around 85-96°C against 100°C. The difference is not temperature but agitation. A boil is thousands of collapsing bubbles delivering mechanical energy, which shreds fish, clouds a stock by emulsifying fat and driving protein scum back into suspension, and breaks the emulsions in cream sauces. A simmer delivers the same heat without the turbulence. This is why almost everything long-cooked wants a simmer: the extra few degrees buy almost nothing and the agitation costs a great deal. The exceptions are when you specifically want that energy — reducing fast, or gelatinising starch in a slurry, which genuinely needs to reach a boil to thicken fully.
The full TO SIMMER lesson — how to tell, where to practise it, what it carries to.