Onion ring

Onion rings (also called French-fried onion rings) is a form of appetizer or side dish in British and American cuisine. They generally consist of a cross-sectional "ring" of onion dipped in batter or bread crumbs and then deep fried; a variant is made with onion paste. While typically served as a side dish, onion rings are often eaten by themselves.

Onion strings are a variant where the onion is cut vertically first, resulting in strips rather than circles.

History
A British recipe from 1802 calls for cutting onions into slices, dipping them into a batter including Parmesan cheese, and deep-frying them in lard. It suggests serving them with a sauce of melted butter and mustard.

Many recipes for deep-fried onion slices or rings are found starting in the early 20th century. There are various processes:
 * no coating: 1902, 1907;
 * dipped in milk or egg and coated in flour: 1902, 1908, 1909, 1910, 1916;
 * battered: 1919, 1922;
 * breaded: 1914.

Food chemistry
The cooking process decomposes propanethial oxide in the onion into the sweet-smelling and tasting bispropenyl disulfide, responsible for the slightly sweet taste of onion rings.