Heavy Cream Resists Curdling

The casein proteins in milk and cream are stable to boiling temperatures, but they’re sensitive to acidity, and the combination of heat and acid will cause them to curdle. Many sauces include flavorful acid ingredients: sauté pans are often deglazed with wine, for example. This means that most milk and cream products, including light cream and sour cream, can’t actually be cooked to make a sauce; they must be added as a last-minute enrichment. The exceptions are heavy cream and crème fraîche, which contain so little casein that its curdling simply isn’t noticeable.