So asks reader LML, and it’s a fascinating question. As you may recall egg white whippers are frequently counseled to add acid to their whites as they first start to foam up. But why exactly is that? Well you’ll recall from the post below that whipping causes egg white proteins to unfold and begin collecting around air bubbles. The trouble is that this same action, if carried too far, will cause the proteins to clump back up again. It’s the excess agitation you see. It causes the protein molecules to bond excessively to their neighbors, and when that happens they coagulate in much the same way they do when they’re exposed to too much heat.
To give ourselves are bigger margin of error when whipping we bakers add various substances to our egg white foams that plug up the proteins’ bonding sites. Copper ions serve that purpose well, which is why more than a few egg white whippers like to use copper bowls. Additives also work nicely. Copper ions can be had in powdered form in health food stores, but vinegar, lemon juice and cream of tartar also work. Those acids don’t affect the proteins’ bonding sites directly, though by changing the pH of the foam they increase the number of free hydrogen molecules floating around, and they gunk up the works almost as well as copper ions.
So the question is: would acids help stop protein coagulation that results from heat in the same way they inhibit coagulation caused by too much whipping? I haven’t tried it, but my gut says yes — up to a point. No amount of acid or copper ions can ultimately stop coagulation if the whipper just keeps on whipping. Likewise no amount of acid or copper can stop proteins from coagulating in high, sustained heat. Yet it probably can provide a buffer. Whether that buffer would make the difference between a dry-ish white cake and moist-ish white cake is open to question. The way to test it would be to make a classic white cake like this twice, once with regular milk and once with buttermilk. Anyone up for the challenge?
LML, fabulous question.