I’ve been making thick drinking chocolate, using the basic milk + chopped chocolate method:

1. heat 1 cup of milk slowly and add chopped chocolate (2.5 oz), whisking thoroughly.

2. once chocolate is incorporated, cool the mixture (at room temp an hour or so, or longer in fridge)

3. when ready to serve: heat, whisking, till the mixture thickens

I am using my own 70% chocolate (only cane sugar and roasted cacao).

My question is, what is happening to make the mixture thicken with the re-heating? It thickens regardless of the type of milk I’m using (even non-fat works). So what is happening with the cacao/butter to cause the thickening? It thickens quite suddenly, when it reaches a certain temperature. It does not thicken with the first heating when initially melting the chocolate. It is quite a lovely texture and flavor, and we won’t make it any other way now. I imagine that the only reason other recipes on the internet include corn starch is to thicken it with the initial heating/melting.

No, no visible oil separation, and no lumps. Before it thickens, I suppose I can sense the very fine grains of my well-melanged chocolate. But that’s barely perceptible, really no different from the texture if I go old-school and make cocoa using gramma’s old-school hershey’s cocoa powder method.

A friend suggested that the milk-fat and the cocoa butter are homogenizing. However, this doesn’t seem accurate to me, since the thickening is exactly the same with non-fat milk.

This kind of problem is difficult to answer without actually seeing your mixture but I suspect it could be a number of things that I’ll just go through. And I will say that I’ve seen this kind of thing myself.

First off I agree it isn’t the milk fat and cocoa butter homogenizing. If anything it would be the opposite. And that may or may not be the case. I agree this isn’t the issue because once something is homogenized, that is it. It means all the oils are wrapped up in water and everything is stable. It’s rather an all or nothing deal. Kind of like pregnancy and death. Once you are one of those, there really isn’t a way to become more pregnant or more dead. And second, the hole goal is to homogenize the chocolate into a liquid. Since that is the goal, it isn’t the problem

Next, I’m going to make a couple observations that may or may not help. When I make hot chocolate from fresh chocolate I make it the other way around. I heat my chocolate and stir in my milk. Just like I do for truffles. I find the emulsion is more stable and does not break as easily. Also, in my experiments I find I use a bit more milk than you are using, and that additional liquid might well be the key. You have a ratio of just over 1:4 chocolate (5:16 technically). My ratio is 1:8 – 1:12. And generally, longer I keep it the more liquid I need which is just what you are seeing.

I see though that it’s thickening for you upon re-heating. That to me points to the culprit being the heating. It may or may not be the temperature itself, but the act. Emulsions are kind of delicate depending on what you do to them. In some cases they are very stable, but in others just break. Generally speaking they are temperature sensitive. They can be stable while hot, but they don’t like agitation. And if you need to stir or shake them, then they need more liquid. So my suspicion is that you are making the perfect storm between heating the mixture and stirring/whisking it too much. I recommend heating in the classic manner of using a double boiler so you don’t have hot spots or a microwave in 15-30 second increments. And stirring VERY gently, not vigorously whisking.

When the emulsion does break (if that is what is happening) I think the reason you are not seeing oil separate is that the chocolate is then immediately seizing and you are seeing it thicken and it is holding the oil in. At that point the chocolate particles start to absorb additional water and the mixture continues to thicken. I’ve seen this a lot in proportions of even 1:10. The only variable is time and the only solution is to continue to add liquid until the chocolate particles are saturated and can start to thin out.

The short of all this is that I can’t give you a 100% effective method for holding hot chocolate. It’s a fresh ‘live ‘ product and best consumed freshly prepared on the spot. Just like many foods like soufflés, rare hamburgers, fresh coffee and innumerable other foods, some things just don’t like to be held and that is just the way it is. And if they are held, it takes a bit of fancy food science and the end result is never quite as good or as special as fresh.

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