The Chemical Weapons of Onions and Garlic

The Curious Cook in the New York wrote The Chemical Weapons of Onions and Garlic. It's basically a review of Dr. Eric Block's book Garlic and Other Alliums: The Lore and the Science. It talks a bit about their history and chemistry. Here's a bit from the end of the review.

"This basic chemistry leads to some general guidelines for cooking.

If you’re using onions or garlic or chives raw, in a dressing or salsa, either chop them just before serving or rinse the chopped pieces thoroughly. Water removes the harsh aging sulfur compounds from the cut surfaces, so you’ll taste only the fresh ones.

If you’re heating garlic or onions or their relatives, then cooking whole or coarsely chopped bulbs will moderate their flavor. Crushing or grating will intensify it.

Crushing can also diversify the flavors that alliums contribute to cooked dishes. They’re valuable ingredients in part because their sulfur chemistry suggests and reinforces savory meat flavors. Last year a German study of meat stews found that by far the strongest contributor to the overall ‘gravy’ aroma was an unusual sulfur compound that came not from the meat, but from the onions and leeks. And that compound appears only after these vegetables have been cut up.

So if you’re counting on alliums to give depth to stews or braises or stocks, then chop them finely or crush or purée them. Heat will eliminate the bite and develop the aroma."