With Valentine”s Day approaching and winter sluggishness sinking in, nothing may sound better than a big box of chocolates. Researchers at UW-Madison”s College of Agricultural and Life Sciences are discovering new ways of using milkfat to make those chocolates keep better.

Serious chocolate lovers can make shelf life irrelevant once they open the box, but keeping qualities are important to manufacturers and retailers. Those qualities depend on storage conditions, the type of cocoa butter used, and how the chocolate was tempered, or made.

In chocolate-making, cocoa butter, sugar, milkfat and other ingredients are added, melted and held at certain temperatures for a certain time. This process requires careful control, said Richard Hartel, professor of food engineering at the University of Wisconsin-Madison. “If cocoa butter does not crystallize correctly, crystals of cocoa butter stick out of the surface of the chocolate, reflect light and create a matte surface,” he said. This hazy white surface is called bloom. While harmless, bloom can be mistaken for mold.

Bloom can also happen when chocolate is stored under poor conditions, said Hartel for example, in the sun on the dash of a car. As the melted chocolate hardens again, it will bloom. Chocolate melts at body temperature, about 95 to 100 degrees F. Even when chocolate is below that temperature and seemingly hard, a portion of the chocolate is not completely crystallized, said Hartel. If the temperature fluctuates and exceeds 85 to 90 degrees F, chocolate can bloom in a matter of weeks.

Several different kinds of cocoa butter are used in making chocolate. “Malaysian and Indonesian cocoa butters are considered hard, Brazilian and other South American cocoa butters are considered soft, and Ivory Coast and other African cocoa butters are in between with medium melting points,” Hartel said. “Each has subtle differences and some are more resistant to bloom than others.”

To help inhibit bloom formation in chocolate made from different cocoa butters, CALS researchers are studying the addition of milkfat and milkfat fractions.

Fats are composed of triglyceride molecules. Milkfat is composed of hundreds of different triglycerides. Cocoa butter contains only three different triglycerides. “When cocoa butter crystallizes as we make chocolate, the triglycerides come together in an ordered lattice arrangement,” said Hartel. “Milkfat alters this structure.”

When chocolate crystallizes it can take one or more different crystalline structures called polymorphs, said Hartel. “By tempering chocolate we are trying to get it into the right polymorph form,” he said.

“Bloom happens when the chocolate changes from the polymorph that we made to a more stable polymorph,” Hartel said. “We think that when we add milkfat we are preventing the chocolate from transforming into the more stable polymorph.”

Milkfat can be modified to be better at inhibiting bloom. Milkfat is separated into higher and lower melting point fractions by filtering off the different triglycerides during crystal formation, said Hartel. Harder fractions, or higher melting-point fractions, can be separated from the softer milkfat.

Hartel added harder and softer milkfat fractions to chocolates made with different cocoa butters and studied the rate of bloom.

“By adding milkfat fractions with the highest melting point we inhibited bloom formation in all of the chocolates,” said Hartel. The fractions with middle-melting points inhibited bloom formation, but to a lesser extent.

“The milkfat fractions with the lowest melting point had no effect on bloom in the chocolate made from Ivory Coast cocoa butter,” said Hartel. “And, the low melting point milkfat fraction actually promoted bloom in the chocolate made from Brazilian and Malaysian cocoa butters.”

The research indicates that the high melting point milkfat fractions, which are the most similar to the cocoa butters, are the most effective in preventing bloom in chocolate, Hartel said.

This is good news to chocolate manufacturers. Using milkfat not only improves the stability of chocolate by inhibiting bloom, but is also cheaper than cocoa butter, said Hartel. One pound of cocoa butter costs between $1.50 and $2; milkfat is about $1 per pound.

While other ingredients can influence bloom, milkfat has a major advantage it keeps chocolate legal. Chocolate and other foods have a standard of identity according to U.S. Food and Drug Administration regulations. “According to the FDA, chocolate is cocoa butter, cocoa solids, sugar, milk ingredients and lecithin an emulsifier made from soybeans,” said Hartel. “That”s all you can put into chocolate, and call it chocolate,” he said. If other ingredients are used, such as vegetable fat, the product has to be labeled imitation chocolate or chocolate-flavored.

Research on crystal formation in chocolate during tempering and storage is being continued by Hartel with support from the Wisconsin Center for Dairy Research and the Wisconsin Milk Marketing Board.