Why does vinegar curdle milk? Would adding pickled capers to a cream sauce curdle it?
Iris A. Brown, Kerhonkson, NY
Shirley Corriher replies: Acid on protein causes the protein to coagulate, because the acid is actually “cooking” the protein strands. When vinegar curdles milk, what you get is a dairy version of scrambled eggs.
As to whether pickled capers cause a cream sauce to curdle, that depends on what else is in the sauce. If the sauce has a reasonable amount of starch, it shouldn’t curdle, since the starch should prevent the acid from coagulating the proteins in the cream. If you want to be certain, mix 1/2 cup cold milk with a teaspoon of cornstarch, heat, stirring, until thickened, and then add some of the pickled capers.
Adding an acidic ingredient to heavy cream doesn’t usually cause curdling. The cream has very few proteins and a lot of fat to coat them. When in doubt, a little cornstarch is always good insurance to prevent curdling. And you should always rinse the capers.