How discontented would our winters be without the glorious promise of oranges, grapefruit, lemons and limes?

These fruits come ripe in the dead of winter, and we crave their lively, sunny flavors during the dark, cold months. Our demand for citrus is so high that when Florida crops were threatened with freezing temperatures in early January, there was an immediate reaction from the orange juice futures market. No wonder: Florida accounts for about 40 percent of the world's supply of orange juice. According to recent U.S. Department of Agriculture figures, frozen orange juice concentrate stores are at 500 million pounds. There were 800 million pounds during the same period last year.

In California, the country's second-largest citrus producer, most of the crop goes to the fresh produce market. Mandarins, such as the Cutie variety, have been gaining popularity year after year. More mandarins are being planted in California these days than any other kind of citrus tree, says Tracy L. Kahn, a botanist and curator of the Citrus Variety Collection at the University of California, Riverside.

Most of us think of the four biggies of citrus fruit, but Kahn oversees a collection of more than 1,000 citrus cultivars. Established in the early 1900s, the collection houses rare and common cultivars, which are used primarily for research. Sometimes that research requires a taste test or two. Or five.

"It's one of the perks of my job," Kahn says. She adds that it is "probably best if we don't go into all of my favorites. I have a lot of favorites."

In cooking, citrus fruits are versatile. Each component — rind, juice and pulp — can serve a different culinary purpose. Lemons and limes are popular in many cuisines, especially Italian, French, Spanish, Thai, Japanese, Chinese, Moroccan and Turkish.

Citrus fruits balance sweetness and bitterness, providing depth of flavor to sweet and savory dishes.

Marc Bianchini, a chef and owner of a restaurant group in Milwaukee, observes that "fruits are very important in what I cook."

All good cooking should have the goal of balancing acids and fats, Bianchini says. Citrus juices provide acidity and can smooth out the richness of fats in savory and sweet foods, he says.

The recipes we have selected to highlight citrus fruits — clementine cake, grapefruit curd tarts, lemon-thyme pork and shrimp ceviche — show what the acid in citrus can do, Bianchini says. A stronger acid such as that from a grapefruit works well in a curd, while clementine imparts sweetness and fragrance to a moist cake, he says.

When making ceviches, the trick is to find the right acid for the fish. Lemon and lime work well with shrimp, Bianchini says; with more delicate fish, chefs will often use coconut milk to offset some of the citrus' acid.

Here are a few more facts to consider when you next savor citrus:

• The citrus season runs from early November to April or May, depending on the fruit. Some varieties bear fruit as late as July.

• Oranges left on the tree will not overripen.

• Citrus fruit is believed to be native to Southeast Asia. The Greeks and Romans were early cultivators of citron, a sour citrus fruit. Columbus brought orange, lemon and citron seeds on his second voyage to the Caribbean.

• Except for Key limes, which come from South Florida, virtually all of the limes sold in the United States come from Mexico.

• The word "ascorbic," from ascorbic acid (vitamin C), means "no scurvy."

• Only 10mg of vitamin C per day will prevent a vitamin C deficiency, which leads to scurvy. But most nutrition experts recommend up to 200mg per day for optimum health and to prevent chronic disease. One medium orange provides 70mg of vitamin C; a medium grapefruit provides 56mg; an 8-ounce glass of orange juice contains about 100mg.

• Limonin, a compound in citrus, has been found to prevent several cancers, including cancers of the mouth, pharynx (directly behind the tongue and nasal cavity), larynx, esophagus and stomach.