Published Saturday, April 14, 2001, in the Contra Costa Newspapers

History runs deep for blood oranges

Master Gardener

Q: I was told recently that the blood orange is a cross between an orange and a pomegranate. Is this true?

A: No, the blood orange (Citrus sinensis L. Speck) and the pomegranate (Punica granatum) are genetically incompatible, and cross-fertilization will not occur.

Experts in the citrus field believe that blood oranges are a natural mutation. At some time in the past, a sweet orange underwent a change at the genetic level that produced an orange with red coloration in the flesh and juice and on the rind. This new trait was interesting enough to someone that they continued to propagate the variety.

Until recently it was believed that the blood orange originated in the Mediterranean, possibly Sicily or Malta. However, there is documented evidence that red oranges were in China as early as the fourth century. A Chinese poem from the eighth century translates as follows:

"At Kiang-Nan in the Kiangsu

There are small scarlet oranges

That the winter doesn't kill

Because the air is truly sweet

At Kiang-Nan."

The first mention of red oranges in Sicily came nine centuries later in the opera "Hesperides" by the Jesuit Ferrari (1646). He describes the fruit Aurantium indicum with pigmented pulp brought to Italy from the Philippines by a Genovese missionary. Blood oranges also appear in a painting by Bartolomeo Bimbi, an artist in Tuscany during the 17th and 18th centuries. And the Florentine botanist Micheli (1679-1737) included illustrations of the characteristics of the wine-colored juice Aurantium hierochunticum in one of his manuscripts.

Blood oranges, along with navel oranges and Valencia oranges, are one of the most cultivated types of oranges. However, they exist as a commercial crop, primarily in the Mediterranean basin where conditions appear to be best for consistent color and flavor. They do not do as well in the cool citrus-growing areas of Southern California or in the humidity of Florida. Strangely enough, the rind coloration is best when the fruit is not exposed to the sun; thus, some growers shade the lower portion of the trees by growing a tall cover-crop such as sesbania.

The red color of blood oranges is due to the presence of chemicals called anthocyanins. These pigments are present in a variety of familiar plants, including hydrangeas, purple cabbage and red grapes. Gardeners are probably familiar with the dependence of hydrangea color on the pH (a measure of acidity) of the soil. The flowers are pink in acidic soil and blue in basic soil. It is the anthocyanins that change color with changes in pH. (To observe this dependency, add a small amount of baking soda --which is "basic" -- to a teaspoon of grape juice or red wine. The liquid will change color from red to purple, but probably will not get basic enough to actually turn blue.)

Note that the pink in pigmented grapefruits is caused by lycopene rather than anthocyanins. Blood oranges do not yield an appealing juice, since the pigments tend to deteriorate during processing and become muddy. But if you try this orange -- with its unique interior color and rich orange flavor with overtones of fresh berries -- you are in for a tasty treat.