Acid to Dairy - curdling

The critical step in many custards, panna cottas, and lemon creams is adding an acidic element (buttermilk, crème fraîche, yoghurt, lemon juice) to a hot cream base without splitting it. Above about 70°C, the acid denatures cream proteins and produces a granular, curdled texture. Pull the cream off the heat, wait until it drops to 60–65°C (140–150°F) - still warm enough for gelatin or other binders to stay active, cool enough that the proteins are stable - then whisk in the cold dairy in a thin, slow stream. Never add cold dairy all at once, and never add it to a still-simmering base.