By Harold McGee
There are around 500 species in the genus Allium, a group of plants in the lily family that are native to northern temperate regions. About 20 are important human foods, and a handful have been prized for thousands of years, as is attested by the well-known lament of the exiled Israelites in the Old Testament: “We remember the fish, which we did eat in Egypt freely; the cucumbers, and the melons, and the leeks, and the onions, and the garlic.” Onions, garlic, and most of their relatives are grown primarily for their underground bulbs, which are made up of swollen leaf bases or “scales” that store energy for the beginning of the next growing season, and which naturally keep well for months. Like the sunchoke and its relatives, the onion family accumulates energy stores not in starch, but in chains of fructose sugars, which long, slow cooking breaks down to produce a marked sweetness. Of course the fresh green leaves of bulb-forming alliums are also eaten, and nonbulbing kinds, including leeks, chives, and some onions, give only their leaves.