I took this post down for the evening because I accidentally created some internecine warfare between a couple of my food science sources and I needed a little time to get my facts straight. Reader Bronwyn (quite helpfully I might add) challenged my early contention that hot syrup doesn’t cook egg whites in any meaningful way. Having had a little past experience taking meringue temperatures, I was sure that there was no real cooking going on. This set off a little debate on what exactly was meant by the term “cooking”, and things got confusing quickly. But anyway, here’s Michael’s original question:
I understand that when you add sugar syrup to egg whites to make Italian Merengue it cooks the whites a bit making it more stable than adding plain sugar. I’m curious if the purpose is the same when adding sugar syrup instead of plain sugar to yolks. I made a recipe for a “chocolate roll” which is to add a “light” sugar syrup to yolks and beat until light and fluffy. Then add in melted chocolate with a bit of coffee. Finally fold in stiffly beaten egg whites. Then bake and then fill the roll with whipped cream. Why would the recipe call for sugar syrup to [be beaten into] the yolks instead of plain sugar ?
The answer is that while egg white proteins don’t actually “cook” when you drizzle in the hot softball stage syrup into them, something related is happening. The syrup goes in at around 220 but loses much of its heat to the air and the cool whites. The proteins do “warm” however to about 130 degrees Fahrenheit. That’s below cooking temperature but enough to cause some of the albumen proteins to draw closer to one another, and that “bunching” helps reinforce the air cells. The result is a denser and more pipe-able foam. The down side being that you have fewer proteins to spread around to other air cells, so the volume of the meringue is lower. The same general principle is in operation in a yolk foam, though being so fatty you obviously don’t get anywhere near the same same volume.
Thanks to Chris and then reader Bronwyn for challenging my original post. We’re all a little bit smarter now…