How does flour protect custards against breaking and cracking?

There must be a cheesecake-making convention out there somewhere, because two very closely related questions (this one and the one below) inbox late last week. Reader Alan notes that some cheesecake recipes call for a little flour (or cornstarch) in the batter as insurance against curdling and cracking. He asks: does that really work? And if so, how?

Well Alan, as you may recall from other posts on the subject, custards are gels that form when egg proteins (in a mixture of eggs, water and fat) are gently heated. The heat encourages these long, bunched-up molecules into uncoil themselves. As they do so, they get tangled up with and/or bond with their neighbors. That has the effect of creating a sort of lattice that restricts the flow of the water (and fat molecules) around them, and the mixture firms. 

However when too much heat is applied, the proteins begin to re-bunch themselves (coagulate). The water between the proteins gets squeezed out, and as discussed below, the custard breaks. The result is a bunch of curds floating in water. Starch molecules protect against this process by getting in among the proteins and stopping the re-bunching process from happening. Of course it only works up to a point. If the intense heat continues for too long you’ll get curdling no matter what.

Me, I’m not a big fan of adding starches to custard batters. They make the finished product a little mealy. Better, I think, to follow the suggestions below and control your heat. It’s really not so hard to do.

2 thoughts on “How does flour protect custards against breaking and cracking?”

  1. Agreed on the no starch/flour! I’ve found that even a teaspoon affects the texture and flavor.

    1. Amen. Custards aren’t much fun if they aren’t silky. Or so says i!

      Cheers,

      – Joe

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