Reader Angela writes with this fascinating question:
I have a question that’s bothered me for years, and it occurred to me recently that you might be able to answer it. I know that when you’re melting chocolate, it’s important not to let any water get into the chocolate or it seizes and gets all grainy. However, why doesn’t chocolate get grainy when you melt it with butter or whisk cream into it? At first I thought it must have something to do with the fat and water being emulsified in the cream/butter, but when you melt butter you break the emulsification so it can’t be that. Any ideas?
Oh I always have ideas, Angela. Whether they’re at all based in reality is another matter. Just ask Mrs. Pastry. You’re very right that the act of melting butter breaks that particular emulsion, however in the process of whisking the remaining fat and water together with chocolate, new emulsions and/or suspensions are created. But let’s back up for a moment.
As you know, molten chocolate “seizes” when a small amount of water is added to it. The water creates a syrup as it combines with the sugar in the chocolate. The syrup is partially absorbed by the cocoa solids, which then swell and stick together. Not many people realize that you can “un-seize” chocolate by adding more water to it, the result being that you create enough syrup so that everything starts to flow again. The chocolate won’t be exactly the same after this process, but at least it’ll be good for something (eating, making chocolate chips, baking into cake, etc.).
When you make a chocolate and cream ganache something similar happens. The water from the cream combines with the sugar in the chocolate to form a large volume of syrup, one which the cocoa solids, cocoa butter droplets and butterfat globules float around in. Technically the product is an emulsion inside a suspension with the syrup as the continuous phase (i.e. the stuff everything is suspended in). It’s all pretty stable as long as there’s a fair amount of cream in the mix. In a very chocolate-heavy ganache the cocoa solids can soak up the water from the surrounding syrup, become engorged, and come into contact with each other. At that point the emulsion inside the suspension fails, the solids clump together and they separate out.
Chocolate melted together with butter is, I believe, the reverse: a suspension within an emulsion, which is to say an emulsion of cocoa butter droplets, butterfat globules and syrup, with the cocoa solids scattered within. These types of concoctions are also highly prone to separating if you a.) use a chocolate that’s too high in cocoa solids or b.) get the mixture too hot, in which case the butterfat globules pop and the whole complicated structure breaks down.
Hope this helps, Angela!