egg yolks
Also known as: egg yolk
The yellow, fat- and lecithin-rich center of an egg, separated from the white; used to enrich, thicken, and emulsify custards, sauces like hollandaise and mayonnaise, and rich doughs. Lecithin is what lets a yolk bind fat and water into a stable emulsion, and yolks thicken at a relatively low temperature, which is why gentle heat is essential.
Buying guidance
The freshest eggs separate most cleanly, since the yolk membrane weakens with age and breaks more easily. Buy eggs sized as "large" unless otherwise specified, since yolk size -- and its fat content -- scales with egg size. Whisk hot liquid into yolks gradually rather than pouring yolks into a hot pot: the reverse order scrambles them almost instantly.
Substitutions
- Whole egg -- adds the white's extra protein and water, thinning the result slightly; fine for custards, not for a rich emulsified sauce.
- Cornstarch or flour slurry -- thickens without the richness or emulsifying power; use where viscosity matters more than flavor and gloss.
Tips & common mistakes
Yolks left over from a recipe that only needed whites are easy to waste, but they enrich almost anything -- stirred into rice, pasta, or a pan sauce off the heat, or turned into a quick custard -- so treat extra yolks as an ingredient in their own right rather than a scrap to toss.
Storage
Raw egg yolks left uncovered form a skin and dry out within minutes -- press plastic wrap directly onto the surface, or cover them with a thin layer of cold water, if they need to sit before use. They don't freeze well plain, since they turn thick and gel-like on thawing; whisking in a pinch of salt or sugar first (matched to whether the dish is savory or sweet) keeps them usable after freezing.