If you’re an experienced custard maker, you’ve likely observed a difference in the makeup of firm or “still” custards vis-à-vis pourable “stirred” varieties. That is, that where one typically calls for whole eggs, the other calls for yolks. This has to do with the difference in the properties of yolk proteins versus white proteins that I discussed in my earlier post. White proteins, being very firm and quick to coagulate, are great for building a custard that has to stand on its own. Yet when it comes to a silky type of dealie like a custard sauce…eh, they’re not so good. Here yolk proteins are more desirable. Surrounded by lots of fatty low-density lipoproteins (LDL’s), they have a hard time holding on to one another, and so create a weaker, more spreadable and/or pourable custard.