Storage conditions compromise texture, quality of chocolate.

Bloom is the main reason why chocolate loses its quality. Bloom compromises the product's visual and textural quality. It occurs when some of the cocoa butter in the chocolate separates from the cocoa solids, usually when the chocolate is stored at elevated temperatures.

Bloom is the result of a polymorphic transformation of fat crystals from unstable to more stable forms. Sugar bloom forms at higher relative humidity. It is caused by the deposition of water from the air onto the chocolate. The water dissolves the sugar on the surface before it diffuses back into the air, allowing the sugar to recrystallize on the surface of the product.

Part of the appeal of chocolate is its smooth mouthfeel. As bloom forms, a change in texture occurs. Scientists at the University of Illinois analyzed the textural and color changes that occurred in dark chocolate and milk chocolate that had been stored under various conditions.

The researchers stored chocolate in incubators at 30 C and 32.2 C; in desiccators at 25 C and at 84.7% and 93.6% relative humidity; in refrigerators at 4 C; in freezers at -20 C; and in a temperature-controlled storage room at 22 C. The product's texture was measured using a commercial texture analyzer with a two-bite compression test (25% compression with force of 20 g). Color changes were measured on a commercial colorimeter. The investigators analyzed the samples in the first, third and fifth week of storage.

During storage, equilibration and textural changes occurred. Milk chocolate samples stored at elevated temperatures exhibited a large decrease in springiness (40%) and cohesiveness (54%), indicating that these samples were easier to deform. This might have been caused by a loss of fat in the chocolate matrix.

Chocolates with sugar bloom were 12% to 15% lighter in color, while samples with fat bloom were 25% to 30% more yellow in color. Samples stored in the refrigerator and freezer underwent the least amount of textural change, but these were the most visually compromised. Researchers feel that there may not be any storage condition that does not compromise either the textural or visual quality of chocolate.

A 2005 study published by the American Heart Association shows that flavonoids found in chocolate can help the blood vessels work more smoothly, perhaps reducing the risk of heart disease. This study suggested that cocoa flavonoids appear to have benefits on vascular function and glucose sensitivity.

Further information. Nicki Engeseth, Department of Food Science and Human Nutrition, University of Illinois Urbana-Champaign, 259 ERML, MC-051, 1201 W. Gregory Dr., Urbana, IL 61801; phone: [phone]; fax: [phone]; email: [e-mail].