Chocolate melts in your hands because the melting point of chocolate is lower than the temperature of the average human skin. The melting point of chocolate falls between 86°F and 93°F. This is significantly lower than the average temperature of the human skin, which is around 92°F to 98.6°F, which is higher than the melting threshold of the cocoa butter, so the heat from your hand raises the temperature of the chocolate and causes it to melt.
When you touch a piece of chocolate, thermal energy moves directly from your warm skin into the solid candy, causing the fats to break down and turn liquid. How fast it melts depends on several factors, including the amount of milk fat and other additives such as lecithin, as well as the amount and composition of the cocoa butter in your piece of chocolate. Recent findings show that the average human body temperature may be cooling down to 97.9°F, which is still higher than the melting point of chocolate, so it will make a mess in your hands for the foreseeable future.
Chocolate comes from the pods of the cacao tree, an understory tropical tree native to the Amazon basin. Pods from the cacao tree contain the beans that people ferment, roast, mill, and otherwise process into chocolate. The finished chocolate usually includes various amounts of cocoa solids and cocoa butter, as well as added ingredients, such as sugar, lecithin, and milk powder.
The beans from the cacao tree contain about 50 percent cocoa butter, which is a main raw ingredient for chocolate manufacturing. Cocoa butter is solid at room temperature but starts to melt at about 93 degrees F—below the average human body temperature.
It consists of three fats in almost equal amounts: palmitic acid, stearic acid, and oleic acid. The exact composition strongly influences cocoa butter’s melting temperature, and chocolate makers sometimes adjust the ratio of these fats to fine-tune that melting point.
Researchers have identified the genetic component in cocoa butter that determines its melting point, a discovery that may lead to more new ways of adjusting melting points.
Most of the chocolate we buy in stores has been tempered. Tempering stabilizes chocolate and gives it a glossy appearance and a pleasing snap when broken. The tempering process involves carefully controlling the heating of chocolate to exact temperatures followed by gradual cooling.
In addition to making chocolate shiny and firm, tempering helps to control its melting qualities. If chocolate melts too fast even at slightly cooler room temperatures, it often means that the fat crystals did not form correctly during the cooling and manufacturing process.
Content for this question contributed by Jason Sadler, resident of Nags Head, Dare County, North Carolina, USA
