Alliums

The Allium genus includes: onions, garlic, and leeks.

The strong, often pungent, flavor of the onion comes from its defensive use of sulfur.

The alliums stores sulfur as chemical ammunition, which float in the cell fluids. An enzyme trigger is held separately in a storage vacuole. When a raw onion, garlic, or leek is chopped, chewed, or otherwise physically damaged, the enzyme trigger is released from its vacuole, breaks the ammunition molecules in half to produce sulfurous molecules, which are strong-smelling and irritating. Some of these molecules are volatile, so they continue to react into other compounds. Exposure to oxygen will affect the reactions and thus the flavor of the raw allium. Chopping, pureeing, and pounding will produce varying results.

If the allium is to be consumed raw, it's best to rinse it first to remove the sulfur compounds, since they will continue to react and become harsher with time and exposure to air.

Lacrimator is the sulfur compound that causes the eyes to water. This compound escapes the onion and goes into the eyes and nose of the onion cutter, where it attacks nerve endings directly. Its effects can be minimized by chilling the onions in ice water 30-60 min.

The method of cooking will also affect how the sulfur compounds react, thus producing a range of characteristic flavors.

Cooking at high temperatures in fat will give the strongest flavors. Blanching garlic inactivates the flavor-generating enzyme, so it gives a milder flavor.