Chocolate Crystals, and the Chemistry behind Tempering Chocolates

When you’re making chocolate confections, chances are you’re going to use a higher grade of chocolates than, say, when you’re going to make chocolate chip cookies or chocolate fudge. Particularly if you’re using pure chocolates, tempering is central to achieving a glossy finish and a clean snap. Tempering also accounts for chocolate’s smooth, velvety texture and its ability to stay solid at room temperature.

Chocolate candy that hasn’t been tempered will be many unattractive things, especially mottled, gritty and crumbly. It won’t last for 48 hours without blooming, a chalky sheen on chocolate surface or white streaks in the chocolate itself.

At the heart of chocolate tempering is cocoa butter, the fundamental component that makes chocolates “real.” Cocoa butter has fatty acids that undergo polymorphous crystallization, meaning they can form six different types of crystal structures at any one time. Tempering will control this propensity in order to obtain chocolate candy of the highest standard: lustrous, smooth, hard, crisp, and rich. Unsweetened (dark or bitter), semi-sweet (milk), or white chocolates have cocoa butter and would need to be tempered if they’re to be of the finest quality.

But why the need to manage cocoa butter crystals when tempering chocolates?

A look into crystals

The molecules in cocoa butter bond together to form crystalline structures, and what crystalline bonds are created or would proliferate depend largely on the temperatures applied to the chocolate.

Like any normal crystals, chocolate crystals also have a melting as well as a “freezing” temperature. Freezing is merely the point at which a substance solidifies as dictated by prevailing temperatures. Water, for example, “melts” or becomes liquid at 32ºF but at temperatures lower than this, crystals begin to form rapidly so that at 0ºF, water turns into ice, its solid phase.

Thus, as temperature levels move towards freezing point, the molecules start bonding together to form crystals. These crystals in turn start crowding into the space previously occupied by the liquid molecules and as temperatures lower, all available space becomes crammed full of crystals--at which point liquid turns into solid. How stable the solid would be would depend on the density and uniformity of size of the crystals created.

This is how the crystals in chocolate solidify as well. In its solid phase, the crystal bonds in tempered chocolate are stable, meaning greater force will be necessary to change or distort its shape. A properly tempered chocolate remains stable at room temperatures, about 68-77ºF (20-25ºC). When heat is applied, usually at 96ºF—the melting point for chocolate, which is a couple of degrees lower than body temperature ( 98ºF/37ºC)—the tempered crystals begin to detach from their bonds and disintegrate.

Temperature therefore is crucial to successful tempering. In order to ensure that chocolate temperatures are accurately maintained at their appropriate ranges, chocolatiers depend on a Mercury-Gauge Chocolate Thermometer. It’s so-designed for tempering purposes and can read temperatures as low as 80ºF. If you’re seriously considering a chocolate candy enterprise, this thermometer would be one of the equipment that you’ll want to have.

What Happens to Chocolate Crystals during Tempering?

You may wonder why you have to heat, then cool, then re-heat chocolate when tempering. There’s a reason behind this rigmarole and it’s all tied up with producing as many crystals as possible; but not just any crystal.

When temperature isn’t controlled during tempering, we know that different crystalline structures would multiply at random. There’s a crystal that dominates tempering at 79ºF but yields to a chocolate that may be firm but has a poor snap and melts all too easily. Another crystal, which proliferates at 97ºF, is indeed hard but takes weeks to form. The most desirable crystal is the Type V structure which produces a glossy, firm chocolate, and has the best and cleanest snap when broken. It’s also the most stable crystalline form, melting only near body temperature.

Chocolate that comes from the chocolate makers are already tempered and contain only Type V. When you begin heating the chocolate and it starts melting, the Type V crystals are destabilized and detach from its bonds. When the chocolate has turned liquid, there are no longer any crystals in the cocoa butter making it possible for all six crystal structures to form again in a subsequent tempering.

Once melted, the temperature on the molten chocolate must be lowered to 80-82°F through mixing, depending on the kind of chocolate you’ll be using. This agitation of the chocolate mush is necessary to encourage the crystallization of Type IV and Type V crystals that’s why you scrape, spread and fold the chocolate over a heat-absorbing surface, like a marble slab, so as to create “seed” crystals. The seeds in turn will serve as models for other crystals to form. Once the chocolate melt has thickened, it means that you’ve created an adequate amount of crystals.

Chocolate is then re-heated gently to eliminate the Type IV crystals so that only the Type Vs remain. For dark (unsweetened or bitter) chocolates, the re-heating level is 88-90° F; for semi-sweet (milk), it’s 86-88° F; and for white, it’s 82-84° F. Note that semi-sweet and white chocolates burn easily and turn lumpy when the heat is too high; turning up the heat to eliminate the lumps will be counterproductive.

Once you’ve tempered chocolate and you start dipping, molding, or sculpting take care that the chocolate doesn’t get out of its correct temperature zones. Should temperatures go below acceptable limits, chocolate will solidify and become useless for working; above this and the crystals disappear as well. Remember to work quickly as chocolate will start to set after five minutes at room temperature. If this happens, you can always use the same chocolate to temper again. One thing you can do is set the chocolate on a bain-marie or a hot pad to extend its ideal tempered state so you’ll have more time for dipping and molding chocolates.