Dilution Demands Delicacy

Nearly all the problems that arise in custard and cream making come from the fact that the egg proteins are spread very thin by the other ingredients. Take the nearly identical recipes for a typical sweet milk custard or a crème anglaise: 1 whole egg, 1 cup/250 ml milk, 2 tablespoons/30 gm sugar. The milk alone increases the volume of the mix—which the proteins must span and knit together—by a factor of 6! And each tablespoon of sugar surrounds every protein molecule in the egg with several thousand sucrose molecules. Because the egg proteins are so outnumbered by water and sugar molecules, the coagulation temperature in a custard is between 10 and 20°F higher than in the undiluted egg, between 175 and 185°F/79–83°C. And the protein network that does form is tender, tenuous, and fragile. Exceed the coagulation range by just 5 or 10°F and the network begins to collapse, forming water-filled tunnels in the custard, grainy curds in the cream.