[Sour Orange, Seville Orange, Bigarade; Citrus aurantium]
A native of Southeast Asia, this was the only type of orange known in Europe until after 1500, and now grows cultivated or wild in most subtropical areas of the world. Many are grown in Andalusia, Spain, for shipment to England and Scotland for the manufacture of marmalade. Peel and oil also find extensive use in flavorings for liquors, candies and the like. It is a popular herbal remedy, said to provide a "safe" form of Ephedrine, but this safety is not medically proven. They tend to be quite seedy, and a bit low in juice.
The most available variety in the U.S. and Europe is the Seville Orange which has a lumpy rind and very tart flesh. It's less sour than a lemon and has a distinctly orangy flavor, but it isn't something most people would want to eat out of hand. The photo specimens were about 3-1/4 inch diameter and weighted 7-3/4 ounces each, but they can be quite a bit smaller or larger. These were purchased from a multi-ethnic market in Los Angeles at 2015 US $0.99 / pound.
More on Citrus.
Buying: Bitter / Sour Oranges are available in Florida, and becoming more available in ethnic produce markets in Southern California. They are very popular in southern Mexico, where their main use is for the juice, used in sauces and marinades.
Storing: Keep cool as with other citrus.
Cooking: Sour orange is used in many marinade recipes, and in Florida for making pies. This type of orange is needed for marmalades, for its high pectin content and the interesting flavor of its peel.
Juice Yield: These oranges are fairly dry. 2 pounds of oranges yielded a thin shade over 1 cup of juice.
Substitute: For Juice, use 1/2 cup Grapefruit Juice, 1/4 cup Orange Juice and 3 Tablespoons Lime Juice. A similar mix can be used for grated peel. Substitutes won't work well for pies and marmalades because the high pectin content of the sour orange will not be available.