Rescues · TO WHISK
Cream turned to butter.
Why it happens
The same failure in fat form — the crystals coalesced. This happens in seconds, and warm cream reaches it faster.
Recovering it
Overwhipped egg white can be partly rescued by whisking in one fresh unwhipped white, which reintroduces intact protein. Cream taken slightly too far comes back with a splash of cold liquid cream folded through; cream that has turned to butter cannot come back, though it is perfectly good butter. Lumpy sauce can be pushed through a sieve, which works completely and is not a defeat.
The mechanism
A whisk's many thin wires cut a liquid into far more small streams than a spoon can, which is why it does three different jobs well. It aerates: egg white proteins unfold at the air-water interface and link into a network around the bubbles, which is why the foam builds progressively and why any trace of fat prevents it, since fat competes for that interface. It disperses: the wires shear lumps apart faster than they can re-form, which is why a sauce whisked as liquid is added stays smooth. And it emulsifies, by tearing fat into droplets small enough for an emulsifier to coat. Temperature and acid both matter for foams — a little acid stabilises egg white by helping the proteins unfold without over-linking, and cream whips only when cold, because it is solid fat crystals that hold the structure.
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