A few weeks ago I rather breezily dismissed “tempering” as just one more case of chef-show fancy-speak. Most of the time it is. It’s become a word that gets thrown around food show sets any time a chef wants a fancier word for “warming”. But you don’t “temper” a pot of chicken stock any more than you “caramelize” a steak. Though everybody may know what you mean, it’s an inexact use of a word with a more specific meaning.
In kitchens, “tempering” usually has to do with slow, careful heating of delicate ingredients. Eggs, for instance. A pastry cream or custard sauce is “temepered” to keep egg yolks from heating too fast, cooking, and separating from the rest of the mixture.
Out in the real world, you generally don’t run into the word “tempering” too much unless you happen to work in a foundry. There, “tempering” is used to describe the process of heating and cooling metal in order to impart certain charcteristics of hardness, elasticity and appearance to it. Interestingly, this is exactly what pastry people do when they “temper” chocolate.
Like molten metal, molten chocolate forms crystals as it cools. These crystals (which are composed of fat) can either be stable or unstable. Depending on which form they take, the very same chocolate can either be firm with a nice glossy sheen, or relatively soft with a dull finish and streaks. If you’ve ever melted down a bar of good chocolate to, say, dip strawberries in, you may have noticed this phenomenon. The dipped berries don’t have the same shine as the chocolate bar. Why not?
The chocolate wasn’t “tempered” is the reason. It was allowed to cool too quickly, which permitted unstable fat crystals to form. It’s those unstable crystals that are responsible for the dull finish and slightly mushy bite. Re-creating that nice shine and good hard “snap” of the chocolate bar is what tempering is all about. But since I have other writing to do just now I can’t get into it. More on the subject after I get a little work done.