Beets are notable for their sweetness, they have the highest sugar content of any vegetable, but they are very low in calories. Their sweet flavor comes through whether the beets are fresh or canned. Unlike many other processed vegetables, canned beets are perfectly acceptable in both taste and texture; if not pickled, their sweet flavor is largely unaffected by the canning process. Fresh beets, however, have twice the folate (folic acid) and potassium, and have a distinctive flavor and a crisp texture not found in canned beets. Fresh beets also supply a nutritional bonus, their green tops are an excellent source of beta carotene, calcium, and iron.
The beets we eat as a vegetable (also called red beets, root beets, and table beets) are a root vegetable with two parts, the root and the edible green leaves. They belong to the botanical species Beta vulgaris, which also includes sugar beets (which are processed for sugar), mangel wurzels (very large bulbs used as animal fodder), foliage beets, and Swiss chard (the latter two grown for their greens, not their roots). All these vegetables are descended from a wild slender rooted plant that grew abundantly in southern Europe. In ancient civilizations, only the green leaves of the beet plant were eaten; the roots, which did not look like modern beets, were used medicinally to treat headaches and toothaches. Beets with sizeable, rounded roots, like those we eat today, were probably developed in the sixteenth century, though it took another 200 years before they gained any popularity as a food.
Fresh beets are always in good supply. They are grown in more than 30 states in the US, and crops are harvested and shipped throughout the year. June through October, however, are peak months, and at the start of the season you can find young beets with small tender roots that are suitable for cooking whole.
If the leaves are attached, and especially if you're planning to eat them, it's preferable that they be small, crisp, and dark green. Leaves that are larger than about 8" are probably too mature to be palatable. Limp, yellowed leaves have lost their nutritional value. However, beets with wilted greens may still be acceptable, because the leaves deteriorate much more quickly than the roots. If the leaves on the beets offered at your market look less than fresh, be sure to check the roots for soundness. If the beets are clip topped, at least 1/2" of the stems (and 2" of the taproot) should remain, or the color will bleed from the beets as they cook.
To reduce moisture loss from the roots, cut off beet greens before storing, but leave at least 1" of the stem attached (tiny leaf topped baby beets can be stored for a day or two with their tops intact). Place the unwashed roots in a plastic bag and store in the refrigerator crisper for up to three weeks. Store the greens separately in the same fashion and use them as soon as possible; they are perishable and will keep for only a few days.
Generally speaking, to preserve their color and nutrients, beets should never be cut or peeled before cooking them in liquid; otherwise, they will "bleed" their rich red juices while cooking and turn an unappetizing dull brown. Scrub the beets gently and rinse well, but be careful not to break the skin, which is thin. Leave at least 1" of stem and don't trim the root.
Cooked beets hold their color better if some acid ingredient is added to the cooking water; vinegar or lemon juice, used in many beet recipes, will keep them a beautiful crimson.
Bake: Dry heat cooking locks in nutrients and intensifies the natural sweetness of beets. It's not a quick method, though: To save time, cook a large quantity of beets at once, then chill some for later use in salads. You can also bake beets when you're baking or roasting something else. Wrap beets in foil, place them in a baking pan, and bake in a 350 to 400°F oven until tender. Unwrap and let stand until they're just cool enough to handle, then peel them while still warm. Cooking time: 1 1/2 to 2 hours, depending on size.
Boil: This is the most common way of cooking beets, but some of the color (and nutrients) will be lost in the cooking water. Place beets in a pot of boiling water, cover, and simmer until the beets are just tender. Cooking time: 40 minutes to 2 hours, depending on the size and the age of the beets.
Microwave: Place one pound of whole beets in a microwaveable dish with 1/4 cup of liquid. Cover and cook until tender. Cooking time: 10 minutes.
Steam: Beets can be cooked in a vegetable steamer over boiling water. Tiny beets can be steam boiled with their leaves attached in a little water with lemon juice and herbs added. Cooking time: 40 minutes.