The Science of Curdling

• Dairy products, including cream, contain fats and the protein, casein. When an acidic ingredient is mixed with cream, a chemical reaction takes place. The proteins in the cream separate from the liquid and coagulate, or become lumped together. The acid essentially cooks the proteins, similar to the process of making scrambled eggs. All types of alcohol are acidic, and have the potential to curdle cream, although some are more acidic than others. Beer, for example, has a pH of 4.0 to 5.0, while most wines are more acidic and fall in the pH range of 2.8 to 3.8. A pH below 7.0 is considered acidic. Acidic ingredients aren't the only cause of curdling, though. Boiling or heating cream at high temperatures can also cause curdling and the less fat in the cream, the more likely it is to curdle.

Read the Label

• To minimize the risk of curdling, use heavy cream, rather than half-and-half or light cream. Heavy cream contains a lot of fat, but few proteins. The fat coats the proteins so they're protected from the acid in alcohol. Skim or low-fat milk is the most difficult dairy product to combine with alcohol. You're almost guaranteed curdling with these. Use the freshest cream available. As cream ages, its pH drops and it eventually becomes sour. The more acidic the dairy product, the more likely it is to curdle when combined with alcohol.

An Ounce of Prevention

• To prevent curdling in cooked dishes and sauces, add the cream last. When making a wine reduction sauce, simmer the wine until it reduces by one-fourth to one-half. Remove it from the heat and allow it to cool slightly. Only then should you add cream. A tablespoon or two is plenty. Adding cornstarch to a sauce can also help prevent curdling. Combine the cornstarch with a little cold water or milk to make slurry and stir it into the sauce. To prevent curdling in mixed drinks, stick with fresh, heavy cream. Combine all the ingredients except the cream in your cocktail shaker and shake vigorously. The ice and additional ingredients help dilute the acidity of the alcohol. Add the cream and stir gently.

A Pound of Cure

• Fixing a broken sauce is fairly simple. Warm some cream gently in a saucepan and slowly whisk in the broken sauce. This technique tempers the sauce and brings the proteins back together. You can also try stirring a cornstarch slurry into a broken sauce. Repairing a curdled cocktail is much more difficult. You can try pouring the drink through a sieve to remove the curdled particles, but in most cases, your best bet is to start from scratch.