They also tend to have a slightly shorter shelf life because they lack the pigment that affords them protection against mold and because they have proportionally more water than the yellows. They are most commonly used in Mexican cuisine. Spanish onions are a large yellow storage onion, as round as a globe. They usually have a slightly higher water content and so generally are less hot, sweeter, somewhat crisper and more perishable then the storage onion. They have some heat just enough to let you know that they mean business.
Spanish onions can substitute for specialty sweet onions out of season.
Uncooked, red onions make a handsome addition to salads of all types. However, when cooked, these onions lose some of their color. Boiling Onions Boiling onions are very small yellow or white storage onions, usually about two inches in diameter. They will be hot to the taste before cooking and are best when left whole and boiled or simmered in a stew. They are crisp, with a surprising sweetness and only after chewing does a little sharpness kick in.