17.5 Buying, storing and preparing vegetables

Buy in season

Buy fresh vegetables by the season. At its peak a vegetable costs the least, there is the most to choose from, and its color, flavor and texture are all at their best.

Grades and packs in the United States

The USDA runs a voluntary grading system for fresh vegetables sold on wholesale markets. It judges appearance, condition and anything else that affects waste or eating quality. The general grades, best first:

• U.S. Extra Fancy
• U.S. Fancy
• U.S. Extra No. 1
• U.S. No. 1

Some vegetables also have grades of their own; onions, for example, can be graded U.S. No. 1 Boilers. Consumer grades, lettered with Grade A as the best, are required only for potatoes, carrots and onions.

Fresh vegetables are sold by weight or by count, in cartons called cases, lugs, bushels, flats or crates. How much each holds depends on the vegetable, its size and the packer. Celery, for example, comes in 55-pound cartons holding from 18 to 48 heads.

Wholesalers can also sell common vegetables such as onions, carrots, celery and lettuce already trimmed, cleaned and cut to order. Diced onion costs more per pound than whole onions, but it can save a great deal of time, labor, trimming loss and storage space. Processed vegetables may lose some nutrients, moisture and flavor.

The USDA also controls organic labels, in four tiers:

• "100 percent organic": only organic ingredients, grown and made without added hormones, pesticides or synthetic fertilizers, from soil that has gone three years without unapproved synthetic products.
• Organic, or the USDA seal: a processed food with 95 percent or more of its ingredients, by weight, organic.
• "Made with organic ingredients": a processed food with 70 to 95 percent.
• Below 70 percent: organic ingredients may be listed on the information panel, but the word organic may not appear on the front.

Choosing the variety for the job

Within one vegetable, the variety matters. Potatoes fall into three groups:

• Mealy, such as Russet Burbank: looks glistening and feels dry and grainy on the tongue. Best baked, mashed or as French fries.
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• All-purpose, such as White Chippewa, Yukon Gold and Klondike Gold: in between.
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• Waxy, such as Red Pontiac: looks translucent and feels pasty and wet on the tongue. Best boiled and in potato salad.
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Variety is not the only thing that makes a potato mealy. Growing conditions count: soil, climate and fertilizer. Storage time counts, since new potatoes tend to be waxy. And storage temperature counts: above 50°F sugar turns back into starch, while below 50°F starch turns into sugar.

Each use has its own standard:

• Boiled Red Pontiac: white and slightly translucent, firm enough to hold its shape with little or no sloughing (outer layers peeling away), and mild and slightly sweet.
• Mashed Russet Burbank: white, glistening, light and fluffy, never pasty or lumpy.
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• Baked Russet Burbank: separate, glistening white particles that feel dry on the tongue.

Sweet potatoes come dry-meated, with mealy yellow to tan flesh, or moist-meated, with soft tan to brownish-red flesh. Moist-meated ones are often called yams, though true yams belong to a different genus. Squashes split the same way: summer squash such as zucchini has a soft rind, much water, little starch and a short storage life; winter squash such as acorn or spaghetti has a hard shell, less water, more starch, yellow or orange flesh, and keeps longer.

Respiration and ripening

Vegetables do not ripen the way fruit does, but they go on breathing, or respiring, after harvest. The faster a vegetable respires, the faster it ages and decays, so leaves wilt and stems and stalks turn dry, tough or woody. The rate depends on the kind of vegetable, how mature it was when picked, and how it is stored.

Ethylene gas speeds ripening. Fruits and vegetables give it off on their own, and it can be used on purpose, especially on fruit-vegetables such as tomatoes. Produce shipped mature but still green can be exposed to ethylene just before sale to bring on its color.

Storing fresh vegetables

A few rules keep stored produce fresh:

• Refrigerate most produce between 2 and 4°C (36 and 39°F), with a few exceptions, such as potatoes, kept warmer.
• Hardy vegetables such as carrots and cabbage last for weeks; delicate ones such as lettuce do not keep and should be bought as fresh as possible.
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• Water left on vegetables softens them and starts rot.
• When storing and rotating stock, take out anything rotting, because one bad piece spoils the rest.

Every refrigerator follows one rule: raw food is stored below cooked and ready-to-eat food, never above it. Keep dairy products out of the vegetable cooler. see chapter 2: Refrigerated storage

For storage, vegetables sort into two groups. Winter squash, potatoes, onions, shallots and garlic keep best between 40 and 60°F (4 and 16°C), ideally in a produce refrigerator of their own; without one, keep them at room temperature somewhere dry and airy. An ordinary refrigerator is too cold for them, because cold turns their starch to sugar and changes their texture and flavor. Most other vegetables keep best at 34 to 40°F (2 to 4°C), with fairly high humidity.

Store greens and other delicate vegetables away from apples, tomatoes, bananas and melons. Those give off a lot of ethylene gas.

Preserved vegetables

Preserving makes vegetables last longer. The main methods are irradiation, canning, freezing and drying. All but drying leave texture and flavor much as they were, and canning and freezing work for cooked vegetables too.

Irradiation treats food with ionizing radiation, usually gamma rays from cobalt 60 or cesium 137. It kills parasites, insects and bacteria, slows ripening and stops sprouting, without noticeably heating the food, so flavor and texture stay the same; some nutrients may be lost. Irradiated vegetables need no pesticide spray after harvest and last longer. In the United States the FDA treats irradiation as a food additive. Grains, fruits and vegetables may receive low doses, and the label must say "Treated with radiation" or "Treated by irradiation".

Canned vegetables are the backbone of many food service menus. The cleaned vegetables are sealed in a can and held at high heat for a set time, which kills spoilage microbes; the sealed can keeps air out and slows decay. The heat also softens most vegetables, costs many vitamins and minerals, and can turn green vegetables a dull olive color. Canned vegetables come out of the can essentially cooked.

The USDA has three grades for canned vegetables. U.S. Grade A, also called Fancy, must be tender, unblemished and of top quality. U.S. Grade B is also called Extra-Select. U.S. Grade C, also called Standard, may be uneven or short on flavor, but it can go into soups and casseroles when cost matters.

Rules for canned vegetables:

• Unopened cans keep at room temperature almost indefinitely.
• After opening a can, move what is left into a proper storage container and refrigerate it.
• Throw out any bulging can at once, without opening it.
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• An unopened can of vegetables is not a potentially hazardous food, unless it is marked "Keep Refrigerated", but an opened one is.

Frozen vegetables are nearly as handy as canned, though they often need some cooking and take up costly freezer space. Freezing holds back spoilage microbes and keeps most nutrients, and green vegetables usually keep their color. Texture still suffers: water in the cells freezes into ice crystals that burst the cell walls. Individually quick-frozen (IQF) vegetables are chilled very fast with cold air blasts, chilled plates, liquid nitrogen or similar means, which keeps the crystals small.

Some frozen vegetables are raw, some blanched to shorten cooking, and some fully cooked, needing only heating. They usually go into the heat still frozen. Once thawed or cooked, keep them in the refrigerator and reheat them as you would fresh vegetables, and never refreeze them. They are graded like canned vegetables and usually come in cases of bags or boxes weighing 1 to 2 pounds (450 to 900 grams) each.

Storing frozen vegetables:

• Store frozen food at -18°C (0°F) or colder. Should it warm above that, food can lose color and vitamins, and cooling it again does not undo the damage.
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• Frozen fruit and vegetables keep for months if well wrapped.
• Anything poorly wrapped gets freezer burn: dry white or gray patches where moisture has been lost, harming texture and flavor.
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• Keep the freezer steady as well as cold, because rising and falling temperatures draw moisture out of the vegetables.

Dried vegetables are mostly beans, peas, peppers, mushrooms and tomatoes. Drying changes flavor, texture and look far more than other methods do. Losing water concentrates flavor and sugar and makes the food last much longer.

Preparing vegetables: protecting nutrients

Once a vegetable is peeled or cut, it starts losing nutrients to the air and to any liquid it sits in. Vitamins gather just under the skin, so peel thinly, or not at all. Cut pieces of even size so they cook evenly and look good on the plate.

Keep raw and ready-to-eat food apart while you work. Use separate cutting boards, cloths, knives, sinks and work areas for raw and ready-to-eat food, or else wash with detergent and sanitize between uses. Wash your hands after touching raw food, before you do anything else. see chapter 2: Cross-contamination and allergens

Rules for cooking any vegetable

Whatever the method, a few rules hold.

• Cook vegetables as briefly as you can, to keep their texture, color and nutrients.
• Cook them as close to service as you can. A steam table keeps cooking whatever sits in it.
• If you must work ahead, blanch the vegetables, refresh them in ice water, refrigerate them and reheat them as needed. see chapter 7: Moist heat
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• To help white and red vegetables keep their color, cook them with a little acid: white wine, vinegar or lemon juice.
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• For a mix of vegetables, cook each kind on its own and combine them after. Cooked together, some would be overdone before others were ready.

Acid, alkali and color

What is in the cooking liquid changes texture and color, most of all with moist heat, though it matters for dry heat too, since those recipes often start with blanched or parboiled vegetables.

Texture. Adding an acid such as wine, vinegar or lemon juice makes vegetables resist softening, so they need longer to cook. An alkaline liquid softens them fast and can make them mushy; it also costs nutrients, thiamin above all, and may add a bitter taste. Tap water, traces of detergent on pans, or baking soda can all make a liquid alkaline. Used on purpose, ⅛ teaspoon (0.6 milliliter) of baking soda per cup (225 milliliters) of dried beans speeds their softening.

Color. Three groups of pigment color vegetables, and most vegetables carry a blend of them.

• Chlorophyll leads in green vegetables: broccoli, spinach, green beans.
• Carotenoids lead in yellow and orange vegetables: carrots, winter squash, tomatoes, red peppers.
• Flavonoids lead in white, red and purple vegetables: cauliflower, beets, red cabbage.

Early in cooking, heat makes colors look brighter, chlorophyll most of all. Acid slowly turns green vegetables a dull olive; a slightly alkaline liquid keeps them green. Flavonoids work the other way round, keeping their color in slight acid and losing it in alkali. Carotenoids do not react to either. Color alone does not change flavor, but a vegetable can look so unappetizing that nobody will eat it.

A vegetable also releases its own acids as it cooks. Put a lid on the pan and those acids build up: good for flavonoid color, bad for chlorophyll. So if color were all that mattered, green vegetables would cook in alkaline liquid and flavonoid vegetables in acid. In practice, the better color usually costs texture and nutrients.

How acid and alkali change color and texture. Alkali always costs thiamin and other nutrients.

Which method suits which vegetable

Cooking breaks down a vegetable's cellulose and gelatinizes its starch. That softens it, makes it easier to digest and gives it a pleasant flavor. The aim is usually to cook briefly, but sometimes looks and nutrition pull apart: the methods that keep color and texture best often lose more nutrients. see chapter 7: Starch gelatinization

• Broiling and grilling cook fast with strong radiant heat, which keeps nutrients and browns the vegetable for a flavor no other method gives. Broil soft vegetables such as tomatoes. Cut carrots, peppers, squash and eggplant into broad, thin slices to grill; thread mushrooms, cherry tomatoes and pearl onions on skewers, soaking wooden skewers in cold water for 15 minutes first. Vegetables have little fat, so brush them with clarified butter or an oil-and-herb marinade. see chapter 8: Fitting the method to the food
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• Roasting and baking mean the same thing for vegetables. They bring out natural sweetness and keep nutrients. Eggplant, winter squash and other hearty vegetables suit them best. Onions, carrots and turnips roasted beside meat flavor the roast and take on its juices. Winter squash and sweet potatoes can be seasoned with brown sugar or honey. see chapter 8: What roasting is
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• Sautéing is quick, so have every vegetable, herb and sauce ready first. Cut the pieces evenly. Quick-cooking kinds such as mushrooms, onions, greens, stalks, summer squash and fruit-vegetables need nothing but washing and cutting. Done right, they are brightly colored and slightly crisp. see chapter 8: Getting the food and the pan ready
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• Pan-frying is less common for vegetables, but floured green tomatoes and floured eggplant slices (for eggplant Parmesan) are pan-fried.
• Deep-frying suits potatoes, squash and mushrooms. Apart from potatoes, most vegetables are breaded or battered first, and the coating usually carries the seasoning. Blanch slow-cooking kinds, like cauliflower and broccoli, first, so the inside cooks before the outside burns. Aim for a crisp, golden outside and a tender center that is not greasy. see chapter 8: Batters and breadings
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• Blanching and parboiling both cook in boiling water; the difference is time. Blanching lasts seconds and can also take away strong or bitter flavors, soften firm foods, fix color or loosen skins; kale, chard, snow peas and tomatoes are blanched for these reasons. Parboiling lasts several minutes, to soften roots, cauliflower, broccoli and winter squash and shorten the final cooking. see chapter 7: Moist heat
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• Boiling suits carrots, cabbage, green beans, turnips, red beets and almost any other vegetable. Boil green vegetables fast in plenty of water to keep color and flavor, but simmer starchy roots slowly so the heat reaches the center. Add acid for white and red vegetables to the water before the vegetables go in.
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• Refreshing, or shocking, means plunging boiled, blanched or parboiled vegetables into ice water the moment they leave the pot, unless they are served straight away. It stops the cooking and keeps the color. Lift them out as soon as they are cold; left soaking, they lose nutrients and flavor.
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• Steaming works in a convection steamer, in a basket over boiling liquid, or by pan-steaming in a covered pan with a little liquid. Steamed vegetables keep their shape better than boiled ones, but they cook very fast, so overcooking is the usual mistake. Pan-steaming suits small pieces such as peas, beans and broccoli or cauliflower florets. Cook over stock or court bouillon for extra flavor. see chapter 9: Steaming vegetables
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• Braising and stewing cook vegetables slowly in a little liquid that reduces to a light sauce. A braise is usually one vegetable, a stew several. Romaine and Boston lettuce, cabbage, Belgian endive and leeks are often braised; a stew may hold garlic, onions, carrots, celery, peppers, tomatoes, eggplant and summer squash. Because the liquid is served too, these dishes keep their flavor, and they hold hot for service longer than most. see chapter 10: Stewing
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• Microwaving is a form of steaming and often needs no added water, so color, flavor, crispness and nutrients hold up well. Any vegetable that steams well can be microwaved, but the ovens are small, so their best use is warming up small amounts that were blanched or part-cooked.
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• Puréeing starts with vegetables baked, boiled, steamed or microwaved. Cook white, red and yellow vegetables quite soft and purée them hot. Refresh green vegetables and purée them cold, or they overcook and lose color.