One of life’s less pleasant surprises is discovering the chocolate bar that you forgot you had in your pocket on a hot day. Two scientists working at Cadbury’s research and development plant in Bourneville, U.K., are fighting that gooey surprise with the invention of chocolate that remains solid even when exposed to temperatures of 40º C (104º F) for more than three hours. Aimed at tropical markets, the “temperature tolerant chocolate” is described in a World Intellectual Property Organization (WIPO) patent application.
Chocolate tastes great, in part, because the cocoa butter and other fats in it melt quickly and smoothly in the mouth. Chocolate softens at about 28ºC (82ºF) and melts at 32 to 35ºC. (90 to 95ºF). That makes for a nice treat, but it also makes chocolate hard to transport and store – especially in tropical regions where climate-controlled vehicles and warehouses are scarce.
This isn't simply a matter of being able to have chocolate that doesn't turn into a mess in your glove box. Chocolate is very temperature sensitive and heat can easily cause it to sag and deform and the fats and sugars can “bloom” out if it's improperly stored, resulting in an unappetizing appearance.
Temperature tolerant chocolate isn't new. In fact, it’s been around since the 1930s. Just before World War II, the U.S. military commissioned companies, most notably Hershey’s, to develop and manufacture chocolate bars for soldiers that could be carried in a pocket or stored at tropical temperatures. Over the years, millions of these were issued as regular or emergency rations and some even went to the Moon on Apollo 15. The most recent version was the “Congo Bar” carried by U.S. forces during the Gulf War.
The problem was that making a chocolate bar that wouldn't melt wasn't hard. What was hard was to make one that people still wanted to eat. The military bars didn't melt and they were nutritious, but they were difficult to eat and they didn't taste very good. That’s because the usual way to keep chocolate from melting was to either add fillers like oat flour and swap the cocoa butter for other fats, which made it taste like a candle, or adding water or glycerol to encourage sugar crystal formation, which made it gritty.
Cadbury's approach is to modify part of the chocolate manufacturing process known as “conching.” Conching is a complex mixing process that causes a number of physical and chemical changes in the chocolate. It can take anywhere between 15 minutes to an entire day depending on the type and quality of the chocolate. The conching machine’s design depends on how much chocolate is being processed, the quality, and whether it's made in batches or by continuous flow, but it generally involves temperature-controlled troughs where the chocolate is constantly pushed about by rollers, rotors or louvres.
In the conch, the chocolate undergoes a number of changes. Conching thoroughly mixes the chocolate, allowing the flavors to come out as it's aerated and volatiles and moisture are allowed to escape. As the chocolate is repeatedly pressed against the trough by the rollers or rotors, the cocoa butter and other fats coat the sugar particles in the mix.
In conventional conching, the sugar particles are completely and evenly coated with fats so that they slip by one another easily, but Cadbury discovered that it could make chocolate more temperature tolerant by refining it after conching instead of just before.
In testing, the temperature tolerant chocolate was heated to 40º C (104º F) for three hours, yet when pressed with a finger it didn't stick or deform. According to the Cadbury patent, the chocolate has a similar texture to Cadbury Dairy Milk and the company sees it being used in chocolate bars, biscuits and snacks in hot regions.