A Whiff of What?

For most people, the smell of hot cocoa brings to mind cold winter days, warm fires and comfy sofas. But to food researcher Peter Schieberle at the Technical University of Munich in Germany, cocoa smells a bit like potato chips, cabbage and armpits.

Food additives and artificial flavorings are gauche in Shieberle’s native Germany, so creating new tastes and smells in existing products involves tinkering with cooking times and temperatures. But cocoa is a particularly complex aromatic mixture, owing to all the fermenting, roasting, grinding, dissolving, heating, pressing and drying behind its production.  “Making cocoa is a sophisticated process,” says Schieberle, “it’s very difficult to explain why cocoa smells like cocoa, so we wanted to identify what was in there.”

To tease out cocoa’s constituent smells, Schieberle slowly heated distilled cocoa to 464°F in a special oven.  As the temperature increased degree-by-degree, different molecules reached their various boiling points, and evaporated into steam. The steam traveled through tiny oven pipes to a special “sniffer” port, where his army of graduate students reported the scent of each. The process is called gas chromatography-olfactometry.

In the end, 35 of 550 compounds in distilled cocoa had an identifiable smell. These included ones that smelled like caramel, malt, honey, roasted or popcorn, and sulfur in addition to ones that whiffed of sweat, cabbage and potato chips. To confirm that these individual smells add up to cocoa’s distinct aroma, Schieberle mixed together the 24 most potent cocoa aroma molecules and put them to the sniff test. Cocoa came back. The results were published in last July’s issue of the Journal of Agricultural and Food Chemistry.

Cocoa is one of the many foods that avid cook and food-lover Scheiberle studies. Of the 25 compounds that create black tea’s odor, a main scent is similar to oatmeal. Schieberle was also the first to unravel the smell of popcorn. The key odor-molecule, 2-acetyl-1-pirroline, gives a nutty, roasted smell also found in basmati rice and the crust of wheat bread. He also took apart two breeds of juice oranges and found a grassy component to their smells. Schieberle has also delved deep into the smell of beer, dissecting out hops, the grain that gives our lagers that nutty flavor. Most often he uncovers known molecules that influence food flavours in new ways. But he also routinely discovers new compounds to add to an ever-growing library of food odors, which includes about 3000 and counting.

The process is not perfect, and Scheiberle relies on his and his students’ sense of smell to catch molecules his oven misses. For example, the oven lost a cocoa compound that smells like beef, but his army of noses caught it later. Because losing just one molecule can kill the whole aroma of a particular food. “If you think of an orchestra with 20 or 25 instruments,” he said, “and lots of musicians, if you take one instrument away, it affects the music.”

Megha’s favorite smells are coffee in the AM, baking bread, basil and freshly cut grass. Raspberries give her the creeps and she avoids smelling them at all costs.