Bad smells add taste appeal.

Some odd-smelling compounds -- including those associated with sweat and rotten eggs -- are responsible for the appeal of foods such as popcorn and chocolate. Flavor compounds in chocolate vary according to the cocoa variety used, the conditions of cocoa bean fermentation and roasting, and the addition of milk solids, nut paste, and vanillin. Over the years, more than 500 flavor compounds have been identified, and researchers have determined which are most important to the taste of milk chocolate. Peter Schieberle, a professor at the Institute for Food Chemistry at the Technical University of Munich, Germany, says the goal of the research was to "guide chocolate makers in selecting the most appropriate raw materials for flavor generation in their products, and to reduce manufacturing time without reducing quality."

Of the 51 strongest odor-active compounds detected in commercial milk chocolate, 12 showed very high "flavor dilution factors," meaning these chemicals can be smelled even at very low...