The flesh of rich avocado varieties readily turns into an unctuous puree without the necessity of any cooking, while leaner varieties retain some crispness and hold up well in sliced form for salads. Avocado flesh is well known for browning rapidly once cut or mashed (p. 269), a problem that can be remedied by adding an acidic ingredient (often lime juice) or by airtight wrapping with a plastic film that blocks oxygen effectively (polyvinylidene chloride, alias saran, is far more effective than polyethylene or PVC). In the case of mashed avocado, this means pressing the wrap directly into the surface. Though not usually cooked - heat generates a bitter compound and brings out an odd, eggy quality - avocados are sometimes added at the last minute to thicken and flavor soups, sauces, and stews.

Sweet Corn The corn that we eat as a vegetable is a fresh version of the same grain that gives us dry, starchy popcorn and cornmeal (chapter 9). Each individual grain on an ear of corn is a miniature fruit that's mainly seed, a combination of a small embryonic plant and its relatively large food supply of storage proteins and starch. We eat fresh corn about three weeks after pollination, while the fruits are immature, their storage tissues still sweet and juicy. Corn owes its typical yellow color to carotenoid pigments, including zeaxanthin (which derives its name from corn, The corn that we eat as a vegetable is a fresh version of the same grain that gives us dry, starchy popcorn and cornmeal (chapter 9). Each individual grain on an ear of corn is a miniature fruit that's mainly seed, a combination of a small embryonic plant and its relatively large food supply of storage proteins and starch. We eat fresh corn about three weeks after pollination, while the fruits are immature, their storage tissues still sweet and juicy. Corn owes its typical yellow color to carotenoid pigments, including zeaxanthin (which derives its name from corn, Zea mays, Zea mays, and is one of the two main eye-protecting antioxidants). There are also white varieties with low carotenoid levels, as well as anthocyanin-colored red and blue varieties, and green ones too. and is one of the two main eye-protecting antioxidants). There are also white varieties with low carotenoid levels, as well as anthocyanin-colored red and blue varieties, and green ones too.

Fresh Corn Carbohydrates and Qualities Fresh corn contains three different forms of carbohydrate that contribute different qualities, and that are present in different proportions depending on the variety. The corn plant produces sugars and sends them to the seed, where they are temporarily held as is and impart sweetness until the cells string them together into large storage molecules. Very large sugar chains get packed into starch granules, which have no taste and lend a chalky texture to uncooked corn. Then there are medium-sized, tasteless sugar aggregates called "water-soluble polysaccharides," which have many short branches of sugar molecules. These bushy structures are small enough to float in dissolved form in the cell fluids, yet large enough that they bind up a lot of water molecules and get in each other's way, and thus thicken the fluid to a creamy, smooth consistency. Fresh corn contains three different forms of carbohydrate that contribute different qualities, and that are present in different proportions depending on the variety. The corn plant produces sugars and sends them to the seed, where they are temporarily held as is and impart sweetness until the cells string them together into large storage molecules. Very large sugar chains get packed into starch granules, which have no taste and lend a chalky texture to uncooked corn. Then there are medium-sized, tasteless sugar aggregates called "water-soluble polysaccharides," which have many short branches of sugar molecules. These bushy structures are small enough to float in dissolved form in the cell fluids, yet large enough that they bind up a lot of water molecules and get in each other's way, and thus thicken the fluid to a creamy, smooth consistency.

Traditional sweet corns derived from a genetic trait that arose in the cultivated fields of pre-Columbian South America, and that reduced starch levels in the maturing fruits while raising both sugar and soluble polysaccharide levels. The fresh kernels were thus sweeter and creamier than standard corns. In the early 1960s, breeders in the United States released new "super-sweet" varieties, with very high sugar levels, little starch, but also fewer soluble polysaccharides: so their kernel fluids are less creamy and more watery (see box). Super-sweet varieties have the advantage of losing less sweetness during shipping and storage - in three days, traditional sweet corn converts half of its sweet sugar into tasteless chains - but some corn lovers consider them too sweet, their flavor one-dimensional.

Preparing Corn While we usually prepare and consume the kernels whole, most of the flavor comes from the inner tissues, so some cooks grate, blend, or juice the raw kernels and separate the fluids from the seed coats, which get increasingly thick and tough with age. Because the fluids contain some starch, they will thicken like a sauce if heated above about 150F/65C. Heating also intensifies the characteristic aroma of corn, which is largely due to dimethyl and hydrogen sulfides and other sulfur volatiles (methane-and ethanethiols). Dimethyl sulfide is also prominent in the aroma of cooked milk and molluscs, which is one reason why corn works so well in chowders. Sweet corn is also dried, which gives it a toasted, light caramel note. The hard, inedible support structure called the cob can lend flavor to vegetable stocks; that flavor is nuttier if the cob is first browned in the oven. While we usually prepare and consume the kernels whole, most of the flavor comes from the inner tissues, so some cooks grate, blend, or juice the raw kernels and separate the fluids from the seed coats, which get increasingly thick and tough with age. Because the fluids contain some starch, they will thicken like a sauce if heated above about 150F/65C. Heating also intensifies the characteristic aroma of corn, which is largely due to dimethyl and hydrogen sulfides and other sulfur volatiles (methane-and ethanethiols). Dimethyl sulfide is also prominent in the aroma of cooked milk and molluscs, which is one reason why corn works so well in chowders. Sweet corn is also dried, which gives it a toasted, light caramel note. The hard, inedible support structure called the cob can lend flavor to vegetable stocks; that flavor is nuttier if the cob is first browned in the oven.

Carbohydrates and the Qualities of Fresh CornThis table gives the proportions in different corns of the carbohydrates that make cooked fresh corn taste sweet and feel creamy or dry in the mouth. The figures are percentages of the corn's fresh weight, when harvested 1821 days after pollination.

Sugars (sweetness) Water-soluble polysaccharides (creaminess) Water-soluble polysaccharides (creaminess) Starch (dryness) Starch (dryness)

Standard corn 6 6.

3 3.

66 66.

Sweet corn 16 16.

23 23.

28 28.

Supersweet corn 40 40.

5 5.

20 20.

Source: A. R. Hallauer, ed., Source: A. R. Hallauer, ed., Specialty Corns. Specialty Corns. 2nd ed. (2001). 2nd ed. (2001).

Baby Corn Miniature or "baby" corn consists of immature, unpollinated ears from full-sized corn varieties, picked two to four days after the silks emerge from the ear, when the cob is still edible, crisp, and sweet. (The rest of the plant becomes animal feed.) The ear may be 24 in/510 cm long and contains 23% sugar. Miniature corn production was developed in Taiwan and advanced in Thailand; Central America has recently become a major source. Miniature or "baby" corn consists of immature, unpollinated ears from full-sized corn varieties, picked two to four days after the silks emerge from the ear, when the cob is still edible, crisp, and sweet. (The rest of the plant becomes animal feed.) The ear may be 24 in/510 cm long and contains 23% sugar. Miniature corn production was developed in Taiwan and advanced in Thailand; Central America has recently become a major source.

Okra Okra comes from the annual plant Okra comes from the annual plant Hibiscus (Abelmoschus) esculentus, Hibiscus (Abelmoschus) esculentus, a member of the hibiscus family, and a relative of roselle (p. 327) and cotton. It originated in either southwest Asia or eastern Africa, and came to the southern United States with the slave trade. The portion that we eat is the immature seedpod or capsule, with its distinctive five-cornered shape, starlike in cross section, and its notoriously slimy mucilage. Plant mucilage is a complex mixture of long, entangled carbohydrate molecules and proteins that helps plants and their seeds retain water. (Cactus and purslane are similarly slimy; the seeds of basil, fenugreek, and flax exude water-trapping mucilage when soaked, and are therefore used as thickeners or to add texture to drinks.) Okra mucilage can be exploited as a thickener in soups and stews (as it is in Louisiana gumbo, either to replace or augment powdered sa.s.safras leaf), or its qualities can be minimized by using dry cooking methods (frying, baking). In Africa, slices of the pod are sun-dried. Okra has a mild flavor (though a relative, a member of the hibiscus family, and a relative of roselle (p. 327) and cotton. It originated in either southwest Asia or eastern Africa, and came to the southern United States with the slave trade. The portion that we eat is the immature seedpod or capsule, with its distinctive five-cornered shape, starlike in cross section, and its notoriously slimy mucilage. Plant mucilage is a complex mixture of long, entangled carbohydrate molecules and proteins that helps plants and their seeds retain water. (Cactus and purslane are similarly slimy; the seeds of basil, fenugreek, and flax exude water-trapping mucilage when soaked, and are therefore used as thickeners or to add texture to drinks.) Okra mucilage can be exploited as a thickener in soups and stews (as it is in Louisiana gumbo, either to replace or augment powdered sa.s.safras leaf), or its qualities can be minimized by using dry cooking methods (frying, baking). In Africa, slices of the pod are sun-dried. Okra has a mild flavor (though a relative, A. moschatus, A. moschatus, produces aromatic seeds from which perfumers extract the musky ingredient ambrette). produces aromatic seeds from which perfumers extract the musky ingredient ambrette).

Okra fruits can be hairy and sometimes even spiny, and their inner layers bear bundles of fibers that thicken and toughen as they mature. Small young fruits three to five days old are the most tender. These subtropical natives are damaged by storage temperatures below about 45F/7C.

Olives Olives are the small fruits of Olives are the small fruits of Olea europaea, Olea europaea, a remarkably hardy, drought-tolerant tree that's native to the eastern Mediterranean region, and that can live and bear for a thousand years. In addition to sustenance, the olive has given us an everyday word: its ancient Greek name a remarkably hardy, drought-tolerant tree that's native to the eastern Mediterranean region, and that can live and bear for a thousand years. In addition to sustenance, the olive has given us an everyday word: its ancient Greek name elaia elaia is the source of the English is the source of the English oil oil (and Italian (and Italian olio, olio, French French huile huile). The pulp layer surrounding the large central seed can be as much as 30% oil, which prehistoric peoples could extract by simple grinding and draining, and used in cooking and lamps, and for cosmetic purposes. Olives are also unusual among our commonly eaten fruits for being extremely unpalatable! They are richly endowed with bitter phenolic compounds, which offer some protection from both microbes and mammals. (Wild olives are eaten and their seeds dispersed mainly by birds, which swallow them whole; mammals chew and damage seeds.) Their bitterness has long been moderated or removed by various curing techniques (p. 295). The dark color of ripe olives comes from purplish anthocyanin pigments in the outer layer of the fruit.

Olive OilAmong food oils, olive oil is unique for being extracted not from a dry grain or nut, but from a fleshy fruit, and for carrying the prominent flavors of that fruit. The most prized olive oils are sold unrefined and shortly after harvest, as fresh as possible, and are used more as a delicious, delicate flavoring in their own right, not as a medium in which to cook other ingredients. Italy, France, and other Mediterranean countries are the largest producers and consumers.

Today, about 90% of the large worldwide crop goes to making olive oil.

Making Olive Oil Olive oil is made from the olive fruits when they are six to eight months old, mature and approaching their maximum oil content, and just beginning to turn color from green to purple; fully ripe fruits develop less of the valued green aroma. The olives are cleaned, coa.r.s.ely crushed, pit and all (sometimes along with some leaves from the tree), and finely ground into a paste to break the fruit cells open and free their oil. The paste is mixed for 2040 minutes to give the oil droplets a chance to separate from the watery ma.s.s of olive flesh and coalesce with each other (this step is called "malaxation"). Then the paste is pressed to squeeze both oil and watery liquid from the solids. More oil, but of lesser quality, is extracted by pressing repeatedly and by heating the paste; oil extracted in the "first cold pressing" is the most delicate and stable, and most likely to yield "extra virgin" oil (below). Finally, the oil is separated from the liquid by centrifuge or other means, and filtered. Olive oil is made from the olive fruits when they are six to eight months old, mature and approaching their maximum oil content, and just beginning to turn color from green to purple; fully ripe fruits develop less of the valued green aroma. The olives are cleaned, coa.r.s.ely crushed, pit and all (sometimes along with some leaves from the tree), and finely ground into a paste to break the fruit cells open and free their oil. The paste is mixed for 2040 minutes to give the oil droplets a chance to separate from the watery ma.s.s of olive flesh and coalesce with each other (this step is called "malaxation"). Then the paste is pressed to squeeze both oil and watery liquid from the solids. More oil, but of lesser quality, is extracted by pressing repeatedly and by heating the paste; oil extracted in the "first cold pressing" is the most delicate and stable, and most likely to yield "extra virgin" oil (below). Finally, the oil is separated from the liquid by centrifuge or other means, and filtered.

The Color and Flavor of Olive Oil The result is an oil that's green-gold from the presence of chlorophyll and carotenoid pigments (beta-carotene and lutein), more or less pungent from a variety of phenolic compounds and certain products of fat breakdown (hexanol), and aromatic from dozens of volatile molecules. These include flowery and citrusy terpenes, fruity esters, nutty and earthy and almondy and hay-like molecules; but above all there are the gra.s.sy, "green"-smelling fragments of fatty acids that are also characteristic of leaf and other green vegetables (artichokes), herbs, and apples. Most of these molecules are generated during the grinding and malaxation, when active enzymes from the damaged fruit cells come into contact with vulnerable polyunsaturated fatty acids in the green chloroplasts. (Leaves are sometimes included in the grinding to supply more chloroplasts.) The oil itself is predominantly monounsaturated (oleic acid) and less vulnerable to oxidation. The result is an oil that's green-gold from the presence of chlorophyll and carotenoid pigments (beta-carotene and lutein), more or less pungent from a variety of phenolic compounds and certain products of fat breakdown (hexanol), and aromatic from dozens of volatile molecules. These include flowery and citrusy terpenes, fruity esters, nutty and earthy and almondy and hay-like molecules; but above all there are the gra.s.sy, "green"-smelling fragments of fatty acids that are also characteristic of leaf and other green vegetables (artichokes), herbs, and apples. Most of these molecules are generated during the grinding and malaxation, when active enzymes from the damaged fruit cells come into contact with vulnerable polyunsaturated fatty acids in the green chloroplasts. (Leaves are sometimes included in the grinding to supply more chloroplasts.) The oil itself is predominantly monounsaturated (oleic acid) and less vulnerable to oxidation.

The Quality of Olive Oil Olive oil quality is judged by its overall flavor and by its content of "free fatty acids," or fatty carbon chains that should be bound up in intact oil molecules but instead are floating free, and that are evidence that the oil is damaged and unstable. Under the regulations of the European Economic Community, "extra virgin" olive oil must contain less than0.8% free fatty acids, "virgin" oil less than 2%. (To date, quality labeling of U.S. oils is not regulated.) Oils with higher free fatty acid levels are usually processed to remove nearly all impurities from the remaining intact oil molecules - including desirable flavor molecules. Producers usually blend such refined or "pure" oil with some virgin oil to give it flavor. Olive oil quality is judged by its overall flavor and by its content of "free fatty acids," or fatty carbon chains that should be bound up in intact oil molecules but instead are floating free, and that are evidence that the oil is damaged and unstable. Under the regulations of the European Economic Community, "extra virgin" olive oil must contain less than0.8% free fatty acids, "virgin" oil less than 2%. (To date, quality labeling of U.S. oils is not regulated.) Oils with higher free fatty acid levels are usually processed to remove nearly all impurities from the remaining intact oil molecules - including desirable flavor molecules. Producers usually blend such refined or "pure" oil with some virgin oil to give it flavor.

Storing Olive Oil The fact that virgin olive oils are unrefined has both desirable and undesirable consequences. Of course the beautiful color and rich flavor are great a.s.sets. The oils also contain significant quant.i.ties of antioxidant substances - phenolic compounds, carotenoids, and tocopherols (vitamin E and relatives) - which make them more resistant than other oils to damage by oxygen in the air. However, the same chlorophyll that colors them also makes them especially vulnerable to damage by light, whose energy the chlorophyll is designed to collect. To prevent "photooxidation" and the development of stale, harsh aromas, olive oil is best stored in the dark - in opaque cans, for example - and in cool conditions, which slow all chemical reactions. The fact that virgin olive oils are unrefined has both desirable and undesirable consequences. Of course the beautiful color and rich flavor are great a.s.sets. The oils also contain significant quant.i.ties of antioxidant substances - phenolic compounds, carotenoids, and tocopherols (vitamin E and relatives) - which make them more resistant than other oils to damage by oxygen in the air. However, the same chlorophyll that colors them also makes them especially vulnerable to damage by light, whose energy the chlorophyll is designed to collect. To prevent "photooxidation" and the development of stale, harsh aromas, olive oil is best stored in the dark - in opaque cans, for example - and in cool conditions, which slow all chemical reactions.

Plantains Plantains are varieties of banana that retain much of their starchiness even when ripe, and are treated like other starchy vegetables. They're described along with their sweeter cousins on p. 378. Plantains are varieties of banana that retain much of their starchiness even when ripe, and are treated like other starchy vegetables. They're described along with their sweeter cousins on p. 378.

Seaweeds Seaweed is a very general term for large plants that inhabit the oceans. Nearly all ocean plants are is a very general term for large plants that inhabit the oceans. Nearly all ocean plants are algae, algae, a biological group that has dominated the waters for close to a billion years, and that gave rise to all land plants, including those that feed us. There are more than 20,000 species of algae, and humans have enjoyed many hundreds of them. They've been especially important foods throughout coastal Asia, in the British Isles, and in places as different as Iceland and Hawaii, where they're among very few native edibles. The j.a.panese use seaweeds as wrappers and to make salads and soups; in China they serve as a vegetable; in Ireland they're mashed up in porridge and thicken desserts. Most seaweeds have a richly savory taste and a fresh aroma reminiscent of the seacoast, which in fact they help to perfume. Many are good sources of vitamins A, B, C, and E, of iodine and other minerals, and when dried may be a third protein. Seaweeds are abundant, renew themselves rapidly over a life span of one or two years, and are easily preserved by drying. In j.a.pan, where they've been cultivated since the 17th century, the farmed production of the seaweed used to wrap sushi is more valuable than the harvest of any other aquacultural product, including fish and sh.e.l.lfish. a biological group that has dominated the waters for close to a billion years, and that gave rise to all land plants, including those that feed us. There are more than 20,000 species of algae, and humans have enjoyed many hundreds of them. They've been especially important foods throughout coastal Asia, in the British Isles, and in places as different as Iceland and Hawaii, where they're among very few native edibles. The j.a.panese use seaweeds as wrappers and to make salads and soups; in China they serve as a vegetable; in Ireland they're mashed up in porridge and thicken desserts. Most seaweeds have a richly savory taste and a fresh aroma reminiscent of the seacoast, which in fact they help to perfume. Many are good sources of vitamins A, B, C, and E, of iodine and other minerals, and when dried may be a third protein. Seaweeds are abundant, renew themselves rapidly over a life span of one or two years, and are easily preserved by drying. In j.a.pan, where they've been cultivated since the 17th century, the farmed production of the seaweed used to wrap sushi is more valuable than the harvest of any other aquacultural product, including fish and sh.e.l.lfish.

Some Prominent Edible Seaweeds

Scientific Name

Uses Uses

Green Algae

Sea lettuce

Ulva lactuca Ulva lactuca

Raw salads, soups Raw salads, soups

Sea grapes

Caulerpa racemosa Caulerpa racemosa

Peppery; eaten fresh or sugarcoated (Indonesia) Peppery; eaten fresh or sugarcoated (Indonesia)

Awonori

Enteromorpha, Monostrema Enteromorpha, Monostrema species species

Powdered condiment (j.a.pan) Powdered condiment (j.a.pan)

Red Algae

Nori, laver

Porphyra Porphyra species species

Oatmeal mush (Ireland); sushi wrappers or fried sheets (j.a.pan) Oatmeal mush (Ireland); sushi wrappers or fried sheets (j.a.pan)

Agar, tengusa

Gracilaria Gracilaria species species

Branching stems; raw, salted, pickled, gelling agent for molded sweets (agar-agar, j.a.panese kanten) Branching stems; raw, salted, pickled, gelling agent for molded sweets (agar-agar, j.a.panese kanten)

Irish moss, carrageen

Chondrus crispus Chondrus crispus

Thickening agent for desserts (carrageenan) Thickening agent for desserts (carrageenan)

Dulse, sea parsley

Palmaria palmata Palmaria palmata

With potatoes, milk, soup, breads (Ireland) With potatoes, milk, soup, breads (Ireland)

Brown Algae

Kelp, kombu

Laminaria Laminaria species species

Soup base (dashi), salads, fried (j.a.pan) Soup base (dashi), salads, fried (j.a.pan)

Wakame