Why does my ganache keep breaking? I'm making truffles, and my ganache keeps coming apart. The chocolate acts like it's overheating, but it's not. I've confirmed the temperature of the water in the double boiler several times, and the chocolate never exceeds 120 degrees. Here's my recipe:

20 oz of chopped chocolate (72%)
1 3/4 cups cream
1/4 cup Cognac
2 tbsp Butter
splash of espresso powder


I'm making this in a double boiler, as I find it usually turns out smoother. I don't know why this recipe isn't working today, I've made it twice and it's failed both times, though I've used the recipe many times over the years.

The only difference is the cognac, but I've used other liquid as flavoring. Is there something in liquor that changes the melting properties of chocolate? The liquid is going in with the chocolate, so it's not seizing.

I've destroyed $40 of Valhrona today, so needless to say, I'd like to know why this is happening.
I found an answer in McGee's 'On Food and Cooking: The Science and Lore of the Kitchen'. 

The basic ganache is 1:1 chocolate:cream (by weight). With lots of chocolate the emulsion can come apart.

In 'Keys to good cooking' McGee describes how to restore a failed ganache. You put it over a double boiler and when it reaches 33ºC y stir it vigorously. If that fails, start with a smaller batch, just like you'd recover mayonnaisse.

McGee recommends letting it sit on the counter to cool slowly overnight.

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