As anyone who has taken a candy bar out of a car glovebox on a hot day can tell you, heat is not a friend to chocolate. And it's not just a matter of discovering that a tasty snack has become a gooey mess. It can also mean going for a nice choccy biccy only to find the chocolate coated with an unappetizing white film. It isn't a mold, it isn't unhealthy, and it doesn't affect the taste, but it is unpleasant and bakers and chocolatiers would rather do without it. To make mid-morning snacks a bit less harrowing, scientists at the Fraunhofer Institute have studied the phenomenon and have come up with the answer for what causes the film to form and how to prevent it.
Making chocolate is complicated and is very sensitive to temperature. That's why chocolate companies have sunk millions of dollars into developing chocolate bars that can be stored without refrigeration in the tropics and still tastes like regular chocolate. The reason is that chocolate doesn't just melt into a sticky mass in the heat, it also undergoes chemical and physical changes that can affect its appearance. One example is the white film often found on improperly stored sweets and baked goods.
The film is called "fat bloom" and is usually the result of storing chocolate at too high or fluctuating temperatures, but there are other underlying causes. Fraunhofer's scientists discovered that the key to the problem is certain points in making the chocolate products. This is especially the case in chocolate coated items. According to Fraunhofer, part of the problem is the demand for chocolate at Christmas that requires companies to start production as early as July to meet their targets. This means storing the goods for weeks at a time, which gives the bloom time to form.
However, the scientists have discovered that the biggest problem is in the process used to coat pastries, waffles, bars, cookies, and other confections and baked goods. For this, the products are coated by running them under a fluid cascade of warm, pre-crystallized chocolate. The goods then go under a cooling channel, which rapidly solidifies and crystallizes the chocolate, turning it into a smooth coating.
So far, that doesn't seem like a problem, but the Fraunhofer scientists say that it is in this coating process that the fat bloom starts to develop because the excess chocolate is recycled to coat more goods. In doing so, it picks up fats that the stream has washed off the baked goods and other items. This excess fat penetrates to the surface in what is known as "fat migration." Because the fat makes the chocolate crystallize more slowly, this leaves the coating too soft and allows the fat to collect and form the bloom.
According to Fraunhofer, the answer seems simple, but the word "fat" covers a lot of materials from coconut oil to shortening to palm kernel fat. Nut oils and lauric fats are particularly bad because they don't mix well with cocoa butter and unravel the chocolate's crystalline structure.
The result of the team's research indicates that by adjusting the temperature, cooling channel, and chocolate recycling, much of the bloom problem can be minimized. Fraunhofer says that it can also help producers by analyzing samples from their production runs and suggest recipe tweaks that could help.