Most vegetables are suitable for grilling, though there are a few delicate exceptions. Densely textured vegetables usually need to be partially or wholly cooked before grilling, and all should be brushed or tossed with oil or butter and salted before being put on the grill. Other flavorings such as herbs, vinegar, lemon juice, and sugar may be used. Each type vegetable should be cut to a uniform thickness. Small vegetables or vegetables cut into bite-size pieces are easiest to deal with when skewered or stir-"fried" in a grill basket.
If you're using charcoal, place the hot coals on one side of the grill, or, if you have a gas grill, light just one side if possible, creating a place to move vegetables from one side to the other to keep them from burning. In general, a moderate- to low-heat fire is desirable. Here is just a partial list of vegetables suitable for grilling, with tips on preparing each.
Artichokes — Trim the artichokes and boil them until just barely tender in salted and acidulated water (add white vinegar or lemon juice, about 1/4 cup per quart of water). Remove the 'choke and cut it in half; brush it with oil, sprinkle it with salt, and grill it, cut side down, until lightly browned.
Asparagus — Brush spears with oil and lightly salt them. Choose thick spears and keep the tips away from the hottest part of the fire. Grill just until crisp/tender.
Corn on the cob — Corn can be grilled in two ways: Peel back the husks, remove the silks, and pull the husks back over the corn before placing it on the fire, or leave the husks pulled back (tied with a strip of the husk and left in place to serve as a convenient "handle." Brush the corn with butter or oil and place it directly on the fire, with the husks off the heat. Turn frequently until the corn is lightly browned.
Eggplant — Cut
into slices or planks, depending on the type of eggplant being used. The
pieces should be at least 1/2 inch thick. Surfaces that will be placed on
the grill should be peeled; otherwise, peeling is optional. Lightly score
the surfaces that will be placed on the grill. Brush the eggplant with oil
and salt and grill until it's completely tender. (In the Middle East,
a whole unpeeled eggplant is oiled, placed on the fire, and grilled, with
frequent turns, until the outside is blackened and the inside is fully
cooked and soft. The eggplant is then cut in half and the flesh scooped out
to use in dips and as a purée.)
Leeks — Trim off the root ends and the tops so that about 3 inches of green remains. (This is for decorative purposes only; the green part is tough and inedible.) Slice each leek in half lengthwise, then brush it with oil, sprinkle it with salt and pepper, and grill until golden brown and very slightly charred, eight to 12 minutes. Do not turn.
Lettuce — Most lettuces are too delicate to grill, but there are exceptions. Cut small heads of romaine, radicchio, or Belgian endive lengthwise, leaving the stem end intact so that the heads won't fall apart. Brush the lettuce lightly with oil and grill it, cut side down, until the cut side is just lightly browned — the lettuce shouldn't be completely wilted.
Mushrooms — Grill portobellos either whole or in 1/2-inch slices. Large cremini (also known as baby portobellos), large shiitake, large button mushrooms, and large oyster mushrooms can also be grilled successfully. Smaller cremini, shiitake, and button mushrooms can be threaded on skewers. All should be brushed with oil and salted and peppered before grilling. Grill until tender and golden brown. In general, delicate wild mushrooms such as morels and chanterelles are not good candidates for grilling.
Onions — Cut into slices at least 1/2 inch thick. Reserve the curved ends for other uses. Pierce the slices with skewers or toothpicks to keep the layers from separating. Small whole onions, such as cippolini or pearl onions, should be parboiled before being used for kebabs. Brush the cut sides of the slices with oil, salt, and pepper and grill the slices on both sides. Onions can be grilled until completely softened or just crisp/tender, depending on the onion's flavor and final intended use.
Peppers — Clean peppers and slice them into strips at least 1/2 inch thick or cut them into sections. Oil the slices lightly, sprinkle them with salt, and grill them to the desired doneness — anywhere from crisp/tender to completely softened. To smoke roast peppers, place whole untrimmed peppers directly over the heat. Grill, turning frequently, until the skin is completely blackened. Place the peppers in a paper or plastic bag and allow them to rest for at least 10 minutes. (The steam helps loosen the skin.) Wipe off the charred skin. It's OK if little bits of the char remain — that's part of the flavor. Wiping off the skin with a paper towel in hand makes things easier. Cut the peppers open over a bowl to catch the juices, and remove the seeds and stems.
Potatoes — Potatoes should be cooked just until completely cooked through before grilling. Do not overcook, or they may crumble during grilling. Trim unpeeled baking potatoes lengthwise into planks about 1 1/2 inches thick. Steam or boil just until tender. Salt and pepper the planks, then grill them until quite brown and crispy on the outside. Round boiling potatoes such as red potatoes can be cut into quarters or large chunks. (Cut before cooking.) Fingerling potatoes may be left whole. Boil or steam and proceed as above. For an extra-crispy crust, whisk a superfine flour such as Wondra into the oil, in the proportion of one part flour to two parts oil, before brushing the potatoes.
Summer squashes such as zucchini, yellow squash, and pattypan — Choose small- to medium-size squashes that do not have large seeds. Cut them into halves or planks of even thickness — at least 1/2 inch. (Zucchini or yellow squash with the blossoms still attached make a lovely presentation, but be sure to keep the blossoms away from direct heat.) Oil the cut squashes, sprinkle them with salt and pepper, and grill them to the desired tenderness. Depending on their thickness and the desired doneness, you may or may not need to turn them.
Sweet potatoes — Peel sweet potatoes and cut them into planks in the manner described above for potatoes, or cut them into quarters. Steam or boil the sweet potatoes just until they're cooked. Brush them with oil, salt, and pepper and grill until golden brown. You may also brush the cut sweet potatoes with equal parts melted butter and brown sugar, but be extra-careful to keep the sugar from burning.)
Tomatoes — Choose tomatoes that are ripe but are still firm. Cut a thin slice off the top of a round tomato; and halve Italian tomatoes. Gently squeeze out some of the seeds. Oil the cut sides, add salt and pepper, and place the tomatoes, cut sides down, on the grill. Grill until the tomatoes are browned and slightly softened; do not overcook, or they'll be mushy.
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