The blood orange is a variety of orange (Citrus × sinensis) with crimson, almost-blood-colored flesh. The fruit is smaller than an average orange; its skin is usually pitted, but can be smooth. The distinctive dark flesh color is due to the presence of anthocyanins, a family of antioxidant pigments common to many flowers and fruit, but uncommon in citrus fruits. The flesh develops its characteristic maroon color when the fruit develops with low temperatures during the night. Sometimes there is dark coloring on the exterior of the rind as well, depending on the variety of blood orange. The skin can be tougher and harder to peel than that of other oranges.
The three most common types of blood oranges are the Tarocco (native to Italy), the Sanguinello (native to Spain), and the Moro, the newest variety of the three. Other less common types include Maltese, Khanpur, Washington Sanguine, Ruby Blood, Sanguina Doble Fina, Delfino, Red Valencia, Burris blood Valencia orange, Vaccaro blood orange, Sanguine grosse ronde, Entre Fina blood orange and Sanguinello a pignu. The Maltese is known to be the sweetest. While also pigmented, Cara Cara Navels and Vainiglia Sanguignos have pigmentation based on lycopene, not anthocyanins like blood oranges.
The Moro is the most colorful of the blood oranges, with a deep red flesh and a rind that has a bright red blush. The flavor is stronger and the aroma is more intense than a normal orange. This fruit has a distinct, sweet flavor with a hint of raspberry. This orange is more bitter than the Tarocco or the Sanguinello. The Moro variety is believed to have originated at the beginning of the 19th century in the citrus-growing area around Lentini (in the Province of Siracusa in Sicily) as a bud mutation of the "Sanguinello Moscato". The Moro is a "deep blood orange", meaning that the flesh ranges from orange-veined with ruby coloration, to vermilion, to vivid crimson, to nearly black.
The name Tarocco is thought to be derived from an exclamation of wonder expressed by the farmer who was shown this fruit by its discoverer. It is a medium-sized fruit and is perhaps the sweetest and most flavorful of the three types. The most popular table orange in Italy, it is thought to have derived from a mutation of the "Sanguinello". It is referred to as "half-blood", because the flesh is not accentuated in red pigmentation as much as with the Moro and Sanguinello varieties. It has thin orange skin, slightly blushed in red tones. The Tarocco is one of the world's most popular oranges because of its sweetness (Brix to acid ratio is generally above 12.0) and juiciness. It has the highest Vitamin C content of any orange variety grown in the world, mainly on account of the fertile soil surrounding Mount Etna, and it is easy to peel. The Tarocco orange is seedless.
The University of California, Riverside Citrus Variety Collection has delineated three subcultivars of Tarocco. The Bream Tarocco, which was originally donated by Robert Bream of Lindsay, California, is of medium to large fruit with few to no seeds. Tarocco #7, or CRC 3596 Tarocco, is known for its flavor, but has a rind with little to no coloration. The Thermal Tarocco was donated by A. Newcomb of Thermal Plaza Nursery in Thermal, California.
The Sanguinello (pron.: //), also called Sanguinelli in the US (the plural form of its name in Italian), discovered in Spain in 1929, has a reddish skin, few seeds, and a sweet and tender flesh. Sanguinello, the Sicilian late "full-blood" orange, is close in characteristics to the Moro. It matures in February, but can remain on trees unharvested until April. Fruit can last until the end of May. The peel is compact, and clear yellow with a red tinge. The flesh is orange with multiple blood-colored streaks.
History and background 
Blood oranges may have originated in either China or the Southern Mediterranean, where they have been grown since the 18th century. They are now the primary orange grown in Italy. The anthocyanins which give the orange its distinct maroon color will only develop when temperatures are low at night, as during the Mediterranean fall and winter. Blood oranges cultivated in the United States are in season from December to March (Texas), and from November to May (California).
As a food 
Blood oranges' red pigment, anthocyanin, is an antioxidant. The pigments begin accumulating in the vesicles at the edges of the segments and at the blossom end of the fruit, and will continue accumulating in cold storage after harvest. Due to its pigments the blood orange contain greater amounts of antioxidants than other oranges. Blood oranges have a unique flavor profile compared to other oranges, being distinctly raspberry-like in addition to the usual citrus notes.
Blood oranges are a source of vitamin C like all citrus fruits. A medium-sized (154g) orange also provides 28% of the recommended daily intake of dietary fiber. Oranges can also be a valuable source of folate, calcium, and thiamine.
Some blood orange juice may be somewhat tart, while other kinds are sweet while retaining the characteristic blood orange taste. The oranges can also be used to create marmalade, and the zest can be used for baking. A popular Sicilian winter salad is made with sliced blood oranges, sliced bulb fennel, and olive oil. The oranges have also been used to create gelato, sorbet and Italian soda. Blood oranges are also popular in vinaigrette-style dressings, and are sometimes used to flavor niche-market beer.
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