Sweet onions are trickier because they look very similar to your average yellow onion. While they may look similar, they taste entirely different than yellow onions do. They lack the sharp, astringent taste of other onions and really do taste sweet.
Typically, these are what you’ll enjoy thinly sliced on top of sandwiches. They can range in color from white to yellow and often have a flattened or squashed appearance. Sweet onions tend to be more perishable than other varieties and should be stored in the refrigerator, unlike their fellow onions.
With their deep purple outer skin and reddish flesh, these are really the black sheep (or more appropriately the purple sheep) in the onion family.
Despite the fact that they look so different, red onions are fairly similar to yellow onions in flavor, though their layers are slightly less tender and meaty. They tend to lean more towards the sour-end of the flavor spectrum. Red onions are most often used in salads, salsas, and other raw preparations for their lovely color and relatively mild flavor.
A quick tip: if you find the flavor of red onions too astringent for eating raw, as many do, try soaking them in water before serving.
What do you think of this important difference between these onions? Do you like a particular kind more than another? Share your thoughts in the comments section below.