Chocolate coating for truffles shrinks as it sets - What to do?

I've been making chocolate truffles recently, and I'm pretty pleased with the result, with one exception.

I make a ganache (different mixtures of cream, butter, chocolate and flavourings) and form into balls. I chill them, and dip in tempered chocolate, and letting is set at room temperature. (I'm tempering the chocolate in a sous-vide water bath at ~33°C, according to Jeff Potter's 'Cooking for Geeks')

The chocolate has great snap, and a good shine, but the chocolate shrinks while it sets, which often causes the coat to crack or a small puncture appears through which the ganache seeps out.

I understand the physics behind it (chocolate shrinks as it sets), but I'm wondering what to do about it. Surely I can't be the first person to have this problem.

• Are you sure it's the chocolate coating shrinking, or could it be the ganache balls expanding? You did say you chilled them before dipping.
– GdD
Mar 21, 2017 at 12:11
• According to 'On Food and Cooking '(2004) p711: "It turns out that tempered chocolate shrinks by about 2% in each dimension as it solidifies, because the fat molecules in the stable crystals are more densely packed than they were in liquid form." He goes on to say that it can cause the thin coating on a candy or truffle to crack, especially if the filling is cold and expands slightly when coated with the warm chocolate." So maybe there's no accepter work-around, or I'm confident that he would have mentioned it. Mar 21, 2017 at 13:20
• I would suggest bringing your ganache balls up to room temperature as a possibility, less temperature change means less expansion, might be worth a try. You could also try double dipping the balls.
– GdD
Mar 21, 2017 at 15:15
• I think the thermal expansion of the filling is close to negligible here. The thermal expansion of water is less than 1 * 10⁻⁴ K⁻¹. thus it would need to heat up more than 200°C in order to equal the 2% expansion given by McGee for the reduction in volume caused by the chocolate setting. If they came from a cold fridge into a warm room we may calculate with a temperature difference of 20°C, so the thermal expansion of the filling will be less than 1/10 of the contraction caused by the phase-change of the coating. Mar 21, 2017 at 15:32
• I don't know how to prevent it, but you shouldn't be working with cold ganache, independently of the expansion/shrinking problem. cooking.stackexchange.com/a/21142/4638.
– rumtscho
Mar 21, 2017 at 17:10