Ask the Alchemist #35

I purchased a 1 oz hobby grade bar mold from your establishment. I have been pleased with the results (good shine and crisp snap) in general, but I am a bit puzzled by a spot in the middle of each bar that has a slightly different sheen where the bar contacts the mold. I’m guessing the center is the slowest area to cool. Is there something I can do to avoid the variation in sheen?

This is the difference in theory and practice. In theory, there should be no difference in hobby molds and professional molds, but in practice there is a difference.

This is a result of it being a hobby mold. A few words about molds. Hobby molds are about 1/3 the thickness of professional molds. First off, the mold is less expensive and great while your chocolate making is, well, a hobby. Funny that. Next, the thinner polycarbonate allows the mold to flex and bend. Over time, these molds will crack along the edges and simply show harder wear. Finally, this flex allows the chocolate to warp the mold as it contracts during the temper.
Now, a few more words about tempering and contracting. As I’ve talked about quite a bit, tempering is the selective crystallization of cocoa butter into Type V crystals. In know, I know. Wah, wah wah, wah wah – I know I lost some of you. Here – go read this. I’ll wait……OK, you are back, let’s keep going. Analogy time. You are stacking pick up sticks.


In your untempered chocolate the cocoa butter (your pickup sticks) are laying every which way. But once you align them, they nestle in, and as you hopefully notice, take up much less space. The same thing happens with nearly every fluid that solidifies (the glaring exception being water that expands when you freeze it (which is why it floats)).

So how does that cause the different sheen? The chocolate is also just ever so slightly adhesive, so as the chocolate sets up in the various molds, it can either come away from the walls smoothly, in one snap (if it is in a very rigid professional mold) or it can pull away slowly (if it is in a flexible hobby mold). And since chocolate does not like to be disturbed while setting up, when it disturbs itself, you see the result as a change in surface appearance.

Unfortunately, what that means is the only real way to avoid that change in appearance and have a ‘professional’ look is to use Professional molds – at least in regards to bar molds.

One final note, as I just thought of it. This is usually only noticeable on these longer, perfectly flat topped molds where there is one long continuous surface. The 2 oz mold shows it some, and the 4 oz bar mold even less, but most of the small cavity hobby molds don’t show this at all, partly because the curves in the surface make the mold naturally more rigid, but also because there is less to pull away at a time.

Finally, it’s sort of interesting this question just came in as due to a decision of one of my main mold suppliers, the hobby mold option for the bar molds has been discontinued.  So, in very short order, once stock runs out, only professional grade will be available.

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