17.2 Mushrooms, truffles and onions

Mushrooms

Mushrooms are fungi. They spread by spores and grow as a stalk with an umbrella-shaped cap. They are not true vegetables, but the kitchen uses and serves them as if they were.

Cultivated kinds include:

• the common white mushroom;
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• shiitake;
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• crimini, also called Italian brown;
• straw;
• enokidake, or enoki;
• cloud ear, also called wood ear or Chinese black.
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The button mushroom is simply the youngest, smallest form of the common mushroom. The portabella, the largest cultivated kind, is a crimini left to grow, and can reach 6 inches (15 centimeters) across.

Mushrooms are sold fresh, canned and dried. They can be up to 80 percent water, so dried mushrooms are often the best value even at hundreds of dollars a pound. Kept somewhere cool and dry, dried mushrooms last for months. To use them, soak them in warm water for about 10 to 20 minutes, until soft.

Choose fresh mushrooms that are clean, with no soft or wet spots. On cultivated mushrooms, open gills (the ridges under the cap) mean they are old. Fresh cultivated mushrooms are sold all year; fresh wild ones mostly in summer and autumn. Fresh mushrooms keep up to 5 days refrigerated, in a container left open. They do not need peeling. If they are dirty, rinse them quickly in cool water just before use; do not soak them.

Truffles

Truffles grow underground, close to the roots of beech or oak trees. The only way to farm them is to plant oak groves where they may grow. The two main kinds are the black Périgord truffle and the white Piedmontese truffle. Fresh truffles are dug in the autumn and rarely sold far from where they are found. Their smell and flavor are so strong, especially in white truffles, that a little flavors a soup, sauce or pasta. Black truffles also garnish dishes and flavor pâtés, terrines and eggs. Imported fresh truffles may run to several hundred dollars a pound, so most kitchens buy them canned, dried or processed.

Olives

The olive is the fruit of a Mediterranean tree. Green olives are picked unripe; black olives are fully ripe. Straight from the tree they are too bitter to eat, so they are washed, soaked and cured or pickled first. A good green olive has smooth, tight skin; a ripe one is glossy, softer and a little wrinkled. Kinds range from the tiny black Niçoise of France to the large purple Kalamata of Greece. Ripe black olives are packed in seven sizes and green olives in eleven, up to super-colossal.

Olives come whole, pitted, sliced, halved or in pieces, and pitted green olives are often stuffed with pimento, jalapeño or almonds. Serve them as a snack or hors d'oeuvre, toss them into salads and pasta, or cook them into breads, soups, sauces, stews and casseroles. Tapenade is a paste of finely chopped ripe olives, used as a dip or a condiment.

Bulb onions

Bulb onions are white, yellow (Bermuda or Spanish) or red. Medium yellow and white onions have the strongest flavor; bigger onions are usually sweeter and milder. Onions flavor a huge range of dishes and are a must in mirepoix. see chapter 21: Mirepoix and seasonings

As a side dish, onions can be deep-fried, roasted, grilled, steamed or boiled. Pearl onions are small, about ½ inch (1.25 centimeters) across, with yellow or white skins and a mild taste. Cook them whole for a side dish, or add them to soups and stews.

Sweet onions include the Vidalia, the Maui, the Walla-Walla, the Super Sweet and the OSO Sweet. They hold more water and sugar and fewer sulfur compounds than other onions. They are best raw, on sandwiches, salads and burgers, because cooking takes away much of their sweetness. Each kind is in season only briefly, somewhere between January and August, and none keeps for more than a few weeks.

Choose onions that are firm, dry and heavy, with dry, brittle outer skins and no sprouts. Store them somewhere cool, dry and airy, and do not refrigerate them until they are cut.

Raw onions are not a potentially hazardous food, but fried onions are. A potentially hazardous food is one that lets disease-causing bacteria grow. see chapter 2: Potentially hazardous foods

Garlic, leeks, scallions and shallots

Garlic is used in nearly every cuisine. A head is made of many small cloves, each in a thin peel, and the whole head is wrapped in papery layers. Of around three hundred kinds, three matter in trade: the common pure white garlic with a sharp taste, a stronger pale pink Mexican garlic, and elephant garlic, as big as an apple and quite mild. Whole heads can be baked or roasted, but most garlic is peeled and sliced, minced or crushed. The finer you crush it, the stronger it tastes. The longer you cook it, the milder it gets. Choose firm, dry heads with tight cloves and no green sprouts. Keep it cool and airy, not in the refrigerator.

Fresh garlic is a non-hazardous food, but fresh garlic in oil is potentially hazardous.

Leeks look like overgrown scallions, with a fat white end and wide green leaves. Their flavor is milder than a bulb onion's, yet sweeter and stronger than a scallion's. Sandy soil gets between the layers, so wash leeks with care. Bake, braise or grill them as a side dish, or use them to flavor stocks, soups and sauces. Choose firm leeks with stiff roots and stems, and pass over any with dry leaves, soft spots or browning.

Scallions, also called green onions or bunch onions, are young bulb onions picked as green stalks. The white base may be long and slim or slightly round. Use them in stir-fries and to flavor other dishes, and slice the green tops into small rings for garnish. Look for clean white bulbs under bright green tops, and pass over limp or slimy leaves.

Shallots look like small onions with one flat side. Peeled, they break into cloves, as garlic does. Their flavor is mild but rich and layered. Many classic sauces and meat dishes start with shallots, and a side dish of shallots can be baked or sautéed. Choose plump, well-shaped shallots that are not dry or sprouting, and keep them cool, dry and out of the refrigerator.