3.6. Chocolate

Tempering chocolate—the process of selectively melting and solidifying the various forms of fat crystals in cocoa butter—can be an intimidating and finicky process. The chocolate must first be melted to above 110°F / 43°C, then cooled to around 82°F / 28°C, and then heated back up and held between 89°F / 31.5°C and 91°F / 32.5°C. Once tempered, you must play a thermal balancing act: too warm, you lose the temper, and too cold, it sets.

It’s not exactly correct to describe chocolate as something that “melts,” because chocolate is a solid sol, a colloid of two different solids: cocoa powder and cocoa fats. The cocoa powder itself can’t melt, but the cocoa fats that surround it can. Cocoa butter contains six different forms of fats, and each form melts at a slightly different temperature.

The six forms of cocoa fat are actually six different crystalline structures of the same type of fat. Once melted, the fat can recrystallize into any of the six forms. It’s for this reason that tempering works at all—essentially, tempering is all about coercing the fats to solidify into the desired forms.

Melting points of the six polymorphs of cocoa fat.


How do scientists tell when something is melting? Two common techniques are used: differential scanning calorimetry (DSC) and x-ray diffraction. In DSC, energy is added to a closed system at a controlled rate, and the temperature of the system is monitored. DSC picks up phase changes (e.g., solid to liquid) because phase changes require energy without a temperature change. X-ray diffraction looks at how x-rays scatter when passed through a sample: with each phase change, the x-ray pattern changes.

It’s not a matter of different types of fats; it’s the structure that the fat takes upon solidifying that determines its form. Two of these forms (Forms V and VI) link together to create a metastructure that gives chocolate a pleasing smoothness and firm snap when broken. Chocolate with a high number of Form V structures is said to be tempered. The other primary forms (I–IV) lead to a chalky, powdery texture. Form VI occurs in only small quantities, due to the temperature range at which it crystalizes. Chocolate that has been exposed to extreme temperature swings will slowly convert to Forms I–IV. Such chocolate is described as having bloomed—the cocoa particles and cocoa fats separate, giving the chocolate both a splotchy appearance and a gritty texture.

To further complicate things, the fats in cocoa butters don’t actually melt at an exact temperature, and the composition of the fats varies between batches. The ratio of the different fats determines their exact melting point, and the ratio varies depending upon the growing conditions of the cocoa plant. The fat in chocolate from beans grown at lower elevations, for example, has a slightly higher melting point than chocolate from beans grown at higher, cooler elevations.

Still, the temperature variances are relatively narrow, so the ranges used here generally work for dark chocolates. Milk chocolates require slightly cooler temperatures, because the additional ingredients affect the melting points of the different crystalline forms. When looking at chocolate for tempering, make sure it does not have other fats or lecithin added, because these ingredients affect the melting point.

Luckily for chocolate lovers worldwide, chocolate has two quirks that make it so enjoyable. For one, the undesirable forms of fat all melt below 90°F / 32°C, while the desirable forms noticeably melt around 94°F / 34.4°C. If you heat the chocolate to a temperature between these two points, the undesirable forms melt and then solidify into the desirable form.

The second happy quirk is a matter of simple biology: the temperature of the inside of your mouth is in the range of 95–98.6°F / 35–37°C, just above the melting point of tempered chocolate, while the surface temperature of your hand is below this point. Sure, a certain sugar-coated candy is known to be made to “melt in your mouth, not in your hands,” but with properly tempered dark chocolate, the sugar coating isn’t necessary (it is necessary for milk chocolate, though, which melts at a temperature lower than that of your hand).


M&Ms were developed in 1940 by Frank C. Mars and his son, Forrest Mars, Sr. During the Spanish Civil War (1936–1939), Forrest saw Spanish soldiers eating chocolate that had been covered in sugar as a way of “packaging” the chocolate to prevent it from making a mess.

How does all of this relate to sous vide cooking? Traditional tempering works by melting all forms of fat in the chocolate, cooling it to a low enough temperature to trigger nucleation formation (i.e., causing some of the fat to crystallize into seed crystals, including some of the undesirable forms), and then raising it to a temperature around 90°F / 32.2°C, where the fats crystallize to make Form V crystals.

This three-temperature process requires a watchful eye and, during the second step, constant stirring to encourage the crystals to form while keeping them small. Water baths allow for a shortcut in working with chocolate: already tempered chocolate doesn’t need to be tempered if you don’t get it any hotter than around 91°F / 32.8°C. The desirable forms of fat won’t melt, so you’re good to go. To melt already tempered chocolate, seal it in a vacuum bag and submerge it in a water bath set to 91°F / 32.8°C. (You can go a degree or so warmer; experiment!) Once it’s melted—which might take an hour or so—remove the bag from the water, dry the outside, and snip off one corner: instant piping bag.

Temperature versus time chart for melting and tempering chocolate.

If you’re going to be working with chocolate on a regular basis, the sous vide hack will probably get tiring. It works, but if you have the dough to spend, search online for chocolate tempering machines. One vendor, ChocoVision, sells units that combine a heat source, a motorized stirrer, and a simple logic circuit that tempers and holds melted chocolate suitable for everything from dipping fruit to coating pastries to filling chocolate molds. Of course, if you have a slow cooker, thermocouple, and temperature controller...

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