On Food and Cooking

short-day onions are planted as seedlings in
the late fall, and harvested before they’re fully
mature in the next spring and early summer.
They’re relatively mild and moist and
perishable, and best kept in the refrigerator. A
special category of spring onion is the “sweet”
onion — “mild” is more accurate — which is
usually a standard yellow spring onion grown
in sulfur-poor soils, and therefore endowed
with half or less of the usual amounts of
sulfur-containing defensive chemicals. The
second major kind of market onion is the
storage onion, grown through the summer and
harvested when mature in the fall, rich in
sulfur compounds, drier, and easily stored in
cool conditions for several months.
White onion varieties are somewhat
moister and don’t keep quite as well as yellow
onions, which owe their color to phenolic
flavonoid compounds. Red onions are
pigmented by water-soluble anthocyanins, but
only in the surface layers of each leaf scale, so