In modern industrial freeze-drying, foods are quickly chilled to as low as 70F/57C, then slightly warmed and subjected to a vacuum, which pulls their water molecules out and dries them. Because the foods aren't heated or exposed to oxygen, their flavor and color remain relatively fresh. Many fruits and vegetables are freeze-dried today and used as is for snack foods, or reconst.i.tuted with water in instant soup mixes, emergency rations, and camping foods.

Fermentation and Pickling: Sauerkraut and Kimchi, Cuc.u.mber Pickles, Olives Fermentation is one of the oldest and simplest means of preserving foods. It requires no particular kind of climate, no cooking, and so no expenditure of fuel: just a container, which can be a mere hole in the ground, and perhaps some salt or seawater. Olives and sauerkraut - fermented cabbage - are familiar examples of fermented fruits and vegetables. An overlapping category is the pickle, pickle, a food preserved by immersion in brine or a strong acid such as vinegar. Brines often encourage fermentation, and fermentation generates preservative acids, so the term "pickle" is applied to both fermented and unfermented preparations of cuc.u.mbers and other foods. Less familiar but intriguing relatives of sauerkraut and olives include North African preserved lemons, the pickled plums, radishes, and other vegetables of j.a.pan, and the highly spiced, multifarious pickled fruits and vegetables of India. a food preserved by immersion in brine or a strong acid such as vinegar. Brines often encourage fermentation, and fermentation generates preservative acids, so the term "pickle" is applied to both fermented and unfermented preparations of cuc.u.mbers and other foods. Less familiar but intriguing relatives of sauerkraut and olives include North African preserved lemons, the pickled plums, radishes, and other vegetables of j.a.pan, and the highly spiced, multifarious pickled fruits and vegetables of India.

The Nature of Fermentation Preserving fruits and vegetables by fermentation is based on the fact that plants are the natural home of certain benign microbes which in the right conditions - primarily the absence of air - will flourish and suppress the growth of other microbes that cause spoilage and disease. They accomplish this suppression by being the first to consume the plant material's readily metabolized sugars, and by producing a variety of antimicrobial substances, including lactic and other acids, carbon dioxide, and alcohol. At the same time, they leave most of the plant material intact, including its vitamin C (protected from oxidation by the carbon dioxide they generate); they often add significant amounts of B vitamins; and they generate new volatile substances that enrich the food's aroma. These benign "lactic acid bacteria" apparently evolved eons ago in oxygen-poor piles of decaying vegetation, and now transform our carefully gathered harvests into dozens of different foods across the globe (see box, p. 308), as well as turning milk into yogurt and cheese and chopped meat into tangy sausages (pp. 44 and 176). Preserving fruits and vegetables by fermentation is based on the fact that plants are the natural home of certain benign microbes which in the right conditions - primarily the absence of air - will flourish and suppress the growth of other microbes that cause spoilage and disease. They accomplish this suppression by being the first to consume the plant material's readily metabolized sugars, and by producing a variety of antimicrobial substances, including lactic and other acids, carbon dioxide, and alcohol. At the same time, they leave most of the plant material intact, including its vitamin C (protected from oxidation by the carbon dioxide they generate); they often add significant amounts of B vitamins; and they generate new volatile substances that enrich the food's aroma. These benign "lactic acid bacteria" apparently evolved eons ago in oxygen-poor piles of decaying vegetation, and now transform our carefully gathered harvests into dozens of different foods across the globe (see box, p. 308), as well as turning milk into yogurt and cheese and chopped meat into tangy sausages (pp. 44 and 176).

Fermentation Conditions and Results While some fruits and vegetables are fermented alone in tightly covered pits or jars, most are either dry-salted or brined to help draw water, sugars, and other nutrients out of the plant tissues, and to provide a liquid to cover the food and limit its exposure to oxygen. The characteristics of the pickle depend on the salt concentration and the fermentation temperature, which determine which microbes dominate and the substances they produce. Low salt concentrations and temperatures favor While some fruits and vegetables are fermented alone in tightly covered pits or jars, most are either dry-salted or brined to help draw water, sugars, and other nutrients out of the plant tissues, and to provide a liquid to cover the food and limit its exposure to oxygen. The characteristics of the pickle depend on the salt concentration and the fermentation temperature, which determine which microbes dominate and the substances they produce. Low salt concentrations and temperatures favor Leuconostoc mesenteroides, Leuconostoc mesenteroides, which generates a mild but complex mixture of acids, alcohol, and aroma compounds; higher temperatures favor which generates a mild but complex mixture of acids, alcohol, and aroma compounds; higher temperatures favor Lactobacillus plantarum, Lactobacillus plantarum, which produces lactic acid almost exclusively. Many pickles undergo a microbial succession, with which produces lactic acid almost exclusively. Many pickles undergo a microbial succession, with Leuconostoc Leuconostoc dominating early and then giving way to dominating early and then giving way to Lactobacillus Lactobacillus as the acidity rises. Some Asian pickles are made not by spontaneous lactic fermentations, but by the addition of another fermented "starter" material, the by-products of producing wine or miso or soy sauce. j.a.panese as the acidity rises. Some Asian pickles are made not by spontaneous lactic fermentations, but by the addition of another fermented "starter" material, the by-products of producing wine or miso or soy sauce. j.a.panese nukazuke nukazuke are unique in employing rice bran, whose abundant B vitamins end up enriching the pickled daikon and other vegetables. are unique in employing rice bran, whose abundant B vitamins end up enriching the pickled daikon and other vegetables.

Problems Problems in vegetable fermentations are generally caused by inadequate or excessive salt concentrations or temperatures, or exposure to the air, all conditions that favor the growth of undesirable microbes. In particular, if the vegetables are not weighted down to keep them below the brine surface, or if the brine surface is itself not tightly covered, a film of yeasts, molds, and air-requiring bacteria will form, lower the brine acidity by consuming its lactic acid, and encourage the growth of spoilage microbes. The results may include discoloration, softening, and rotten smells from the breakdown of fats and proteins. Even the helpful Problems in vegetable fermentations are generally caused by inadequate or excessive salt concentrations or temperatures, or exposure to the air, all conditions that favor the growth of undesirable microbes. In particular, if the vegetables are not weighted down to keep them below the brine surface, or if the brine surface is itself not tightly covered, a film of yeasts, molds, and air-requiring bacteria will form, lower the brine acidity by consuming its lactic acid, and encourage the growth of spoilage microbes. The results may include discoloration, softening, and rotten smells from the breakdown of fats and proteins. Even the helpful Lactobacillus plantarum Lactobacillus plantarum can generate an undesirably harsh acidity if the fermentation is too vigorous or prolonged. can generate an undesirably harsh acidity if the fermentation is too vigorous or prolonged.

Unfermented, Directly Acidified Pickles There are also a host of fruit and vegetable products that are pickled not by fermentation, but by the direct addition of acid in the form of wine or vinegar, which inhibits the growth of spoilage microbes. This ancient technique is much faster than fermentation and allows greater control over texture and salt content, but it produces a simpler flavor. Today, the usual method is to add enough hot vinegar to produce a final acetic acid concentration of around 2.5% (half that of standard vinegar) in such materials as beans, carrots, okra, pumpkin, mushrooms, watermelon rind, pears, and peaches. Nonfermented pickles are usually heat-treated (185F/85C for 30 minutes) to prevent spoilage. The simple flavor of directly acidified pickles is often augmented by the addition of spices and/or sugar. There are also a host of fruit and vegetable products that are pickled not by fermentation, but by the direct addition of acid in the form of wine or vinegar, which inhibits the growth of spoilage microbes. This ancient technique is much faster than fermentation and allows greater control over texture and salt content, but it produces a simpler flavor. Today, the usual method is to add enough hot vinegar to produce a final acetic acid concentration of around 2.5% (half that of standard vinegar) in such materials as beans, carrots, okra, pumpkin, mushrooms, watermelon rind, pears, and peaches. Nonfermented pickles are usually heat-treated (185F/85C for 30 minutes) to prevent spoilage. The simple flavor of directly acidified pickles is often augmented by the addition of spices and/or sugar.

Pickle Texture Most pickled fruits and vegetables are eaten raw as a condiment, and are preferred crisp. The use of unrefined sea salt improves crispness thanks to its calcium and magnesium impurities, which help cross-link and reinforce cell-wall pectins. Especially crisp cuc.u.mber and watermelon-rind pickles are made by adding alum (aluminum hydroxide), whose aluminum ions cross-link cell-wall pectins, or by presoaking the raw materials in a solution of "pickling lime," or calcium hydroxide, whose calcium ions do the same. (Lime is strongly alkaline and its excess must be washed from the ingredients before pickling to avoid neutralizing the pickles' acidity.) When subsequently cooked, pickles may not soften because their acidity stabilizes cell walls (p. 282). Tender pickles are produced by precooking the vegetable until soft. Most pickled fruits and vegetables are eaten raw as a condiment, and are preferred crisp. The use of unrefined sea salt improves crispness thanks to its calcium and magnesium impurities, which help cross-link and reinforce cell-wall pectins. Especially crisp cuc.u.mber and watermelon-rind pickles are made by adding alum (aluminum hydroxide), whose aluminum ions cross-link cell-wall pectins, or by presoaking the raw materials in a solution of "pickling lime," or calcium hydroxide, whose calcium ions do the same. (Lime is strongly alkaline and its excess must be washed from the ingredients before pickling to avoid neutralizing the pickles' acidity.) When subsequently cooked, pickles may not soften because their acidity stabilizes cell walls (p. 282). Tender pickles are produced by precooking the vegetable until soft.

Some Fermented Vegetables and Fruits Adapted from G. Campbell Platt, Fermented Foods of the World Fermented Foods of the World - - A Dictionary and Guide A Dictionary and Guide (London: b.u.t.terworth, 1987). (London: b.u.t.terworth, 1987).

Fermented Cabbage: Sauerkraut and Kimchi Two popular styles of cabbage pickles ill.u.s.trate the kind of distinctiveness that can be achieved with slight variations in the fermentation process. European sauerkraut is a refreshing side dish for rich meats, and Korean kimchi is a strong accompaniment to bland rice. Sauerkraut - the word is German for "sour cabbage" - is made by fermenting finely shredded head cabbage with a small amount of salt at a cool room temperature; it's allowed to become quite tart and develops a remarkable, almost flowery aroma thanks to some yeast growth. Kimchi is made by fermenting intact stems and leaves of Chinese cabbage together with hot peppers and garlic, and sometimes other vegetables, fruits (apple, pear, melon), and fish sauce. More salt is used, and the fermentation temperature is significantly lower, a reflection of its original production in pots partly buried in the cold earth of late autumn and winter. The result is a crunchy, pungent pickle that is noticeably less acid but saltier than sauerkraut, and may even be fizzy due to the dominance of gas-producing bacteria below about 58F/14C. Two popular styles of cabbage pickles ill.u.s.trate the kind of distinctiveness that can be achieved with slight variations in the fermentation process. European sauerkraut is a refreshing side dish for rich meats, and Korean kimchi is a strong accompaniment to bland rice. Sauerkraut - the word is German for "sour cabbage" - is made by fermenting finely shredded head cabbage with a small amount of salt at a cool room temperature; it's allowed to become quite tart and develops a remarkable, almost flowery aroma thanks to some yeast growth. Kimchi is made by fermenting intact stems and leaves of Chinese cabbage together with hot peppers and garlic, and sometimes other vegetables, fruits (apple, pear, melon), and fish sauce. More salt is used, and the fermentation temperature is significantly lower, a reflection of its original production in pots partly buried in the cold earth of late autumn and winter. The result is a crunchy, pungent pickle that is noticeably less acid but saltier than sauerkraut, and may even be fizzy due to the dominance of gas-producing bacteria below about 58F/14C.

Cuc.u.mber Pickles Today there are three different styles of cuc.u.mber pickle in the United States, and the two most common are really flavored cuc.u.mbers; they don't keep unless refrigerated. True fermented cuc.u.mbers have become relatively hard to find. Today there are three different styles of cuc.u.mber pickle in the United States, and the two most common are really flavored cuc.u.mbers; they don't keep unless refrigerated. True fermented cuc.u.mbers have become relatively hard to find.

All cuc.u.mber pickles start with thin-skinned varieties that are harvested while immature so that the seed region hasn't yet begun to liquefy, and cleaned of flower remnants that harbor microbes with enzymes that cause softening. Fermented cuc.u.mbers are cured in a 58% brine at 6468F/1820C for two to three weeks, and acc.u.mulate 23% salt and 11.5% lactic acid: so they're relatively strong. Such pickles are sometimes moderated before bottling by soaking out some salt and lactic acid, and adding acetic acid. The most common style of cuc.u.mber pickle, crisper and more gentle in flavor, is made by soaking the cuc.u.mbers briefly in vinegar and salt until they reach 0.5% acetic acid and 03% salt, and then pasteurizing them before bottling. Such pickles need to be refrigerated after opening. Finally, there are the freshest-tasting but very perishable pickles, which are soaked in vinegar and salt but not pasteurized. They are kept refrigerated from the moment they're packaged.

Fermented Cabbage Two WaysThe German and Korean versions of fermented cabbage are made differently and develop distinctive qualities.

Sauerkraut

Kimchi Kimchi

Piece size

1 mm shreds 1 mm shreds

Small leaves and stems Small leaves and stems

Ingredients other than cabbage and salt

None None

Chillis, garlic, fish sauce Chillis, garlic, fish sauce

Fermentation temperature

6476F/1824C 6476F/1824C

4157F/514C 4157F/514C

Fermentation time

16 weeks 16 weeks

13 weeks 13 weeks

Final salt content

12% 12%

3% 3%.

Final acidity

11.5% 11.5%

0.40.8% 0.40.8%

Qualities

Tart, aromatic Tart, aromatic

Strong flavor, crunchy, tingly Strong flavor, crunchy, tingly

Common problems in home-pickled cuc.u.mbers include cheesy and rancid off-flavors, which come from the growth of undesirable bacteria when there's not enough salt or acidity to inhibit them, and hollow "bloaters," which are pickles swollen with carbon dioxide produced by yeasts (or sometimes by Lactobacillus brevis Lactobacillus brevis or or mesentericus mesentericus) when the salt level is too high.

Olives Fresh olives are practically inedible thanks to their ample endowment of a bitter phenolic substance, Fresh olives are practically inedible thanks to their ample endowment of a bitter phenolic substance, oleuropein, oleuropein, and its relatives. The olive tree was first cultivated in the eastern Mediterranean around 5,000 years ago, probably as a source of oil. Olive fermentation may have been discovered when early peoples learned to remove the bitterness by soaking the fruit in changes of water. By Roman times, the soaking water was often supplemented with alkaline wood ashes, which cut the debittering period from weeks to hours. (The modern industrial treatment is a 13% solution of sodium hydroxide, or lye.) Alkaline conditions actually break bitter oleuropein down, and also breach the waxy outer cuticle and dissolve cell-wall materials. These effects make the fruit as a whole more permeable to the salt brine that follows (after a wash and acid treatment to neutralize the alkalinity), and help the fermentation proceed faster. Lactic acid bacteria are the main fermenters, though some yeasts also grow and contribute to the aroma. Olives may be debittered and fermented while still green ("Spanish" style, the major commercial type) or once their skin has turned dark with purplish anthocyanins, when they are less bitter. and its relatives. The olive tree was first cultivated in the eastern Mediterranean around 5,000 years ago, probably as a source of oil. Olive fermentation may have been discovered when early peoples learned to remove the bitterness by soaking the fruit in changes of water. By Roman times, the soaking water was often supplemented with alkaline wood ashes, which cut the debittering period from weeks to hours. (The modern industrial treatment is a 13% solution of sodium hydroxide, or lye.) Alkaline conditions actually break bitter oleuropein down, and also breach the waxy outer cuticle and dissolve cell-wall materials. These effects make the fruit as a whole more permeable to the salt brine that follows (after a wash and acid treatment to neutralize the alkalinity), and help the fermentation proceed faster. Lactic acid bacteria are the main fermenters, though some yeasts also grow and contribute to the aroma. Olives may be debittered and fermented while still green ("Spanish" style, the major commercial type) or once their skin has turned dark with purplish anthocyanins, when they are less bitter.

Olives are also fermented without any preliminary leaching or alkaline treatment, but this results in a different kind of fermentation. Nutrients for the microbes in the brine diffuse very slowly from the flesh through the waxy cuticle, and the intact phenolic materials inhibit microbial growth. So the temperature is kept low (5564F/1318C), and yeasts rather than lactic acid bacteria dominate in a slow alcoholic fermentation that takes as long as a year. This method is usually applied to black ripe olives (Greek, Italian Gaeta, French Nicoise). They turn out more bitter and less tart than the pretreated kinds (an acidity of 0.30.5% rather than 1%), and have a distinctively winey, fruity aroma.

Unfermented "ripe black olives" are an invention of the California canning industry. They're made from unripe green olives, which may undergo an incidental and partial fermentation while being stored in brine before processing. But their unique character is determined by repeated brief lye treatments to leach out and break down oleuropein, and the addition of an iron solution and dissolved oxygen to react with phenolic compounds and turn the skin black. Olives so treated are then packed in a light 3% brine, canned, and sterilized. They have a bland, cooked flavor and often some residual alkalinity, which gives them a slippery quality.

Unusual Fermentations: Poi, Citron, Preserved Lemons Poi is a Hawaiian preparation of taro root (p. 306). The starchy taro is cooked, mashed, thinned with water, and then allowed to stand for one to three days. Lactic acid bacteria sour it, and produce some volatile acids as well (vinegary acetic, cheesy propionic). In longer fermentations, yeasts and Poi is a Hawaiian preparation of taro root (p. 306). The starchy taro is cooked, mashed, thinned with water, and then allowed to stand for one to three days. Lactic acid bacteria sour it, and produce some volatile acids as well (vinegary acetic, cheesy propionic). In longer fermentations, yeasts and Geotrichum Geotrichum molds also grow and contribute fruity and mushroomy notes. molds also grow and contribute fruity and mushroomy notes.

Citron peel, candied from a relative of the lemon, owes its traditionally complex flavor to fermentation. Originally the citron fruits were preserved for some weeks in seawater or a 5 to 10% brine while they were shipped from Asia and the Middle East to Europe; now they're brined to develop flavor. Yeasts grow on the peel and produce alcohol, which then supports acetic acid bacteria. The result is the production of volatile esters that deepen the aroma of the peel. The preserved lemons of Morocco and other north African countries have a similar character; they're made by packing cut lemons with salt and fermenting for days to weeks.

Sugar Preserves Another venerable technique for preserving fruits is to boost their sugar content. Like salt, sugar makes the fruit inhospitable to microbes: it dissolves, binds up water molecules, and draws moisture out of living cells, thus crippling them. Sugar molecules are quite heavy compared to the sodium and chloride ions in salt, so it takes a larger ma.s.s of sugar to do the same job of preserving. The usual proportion by weight of added sugar to fruit is about 55 to 45, with sugar accounting for nearly two-thirds of the final cooked mixture. Of course sugar preserves are very sweet, and this is a large part of their appeal. But they also develop an intriguing consistency otherwise found only in meat jellies - a firm yet moist solidity that can range from stiff and chewy to quiveringly tender. And they can delight the eye with a crystalline clarity: in the 16th century, Nostradamus described a quince jelly whose color "is so diaphanous that it resembles an oriental ruby." These remarkable qualities arise from the nature of pectin, one of the components of the plant cell wall, and its fortuitous interaction with the fruit's acids and the cook's added sugar.

The Evolution of Sugar Preserves The earliest sugar preserves were probably fruit pieces immersed in syrupy honey (the Greek term for quinces packed in honey, The earliest sugar preserves were probably fruit pieces immersed in syrupy honey (the Greek term for quinces packed in honey, melimelon, melimelon, gave us the word gave us the word marmalade marmalade) or in the boiled-down juice of wine grapes. The first step toward jams and jellies was the discovery that when they were cooked together, sugar and fruit developed a texture that neither could achieve on its own. In the 4th century CE CE, Palladius gave directions for cooking down shredded quince in honey until its volume was reduced by half, which would have made a stiff, opaque paste similar to today's "fruit cheese" (spreadable "fruit b.u.t.ter" is less reduced). By the 7th century there were recipes for what were probably clear and delicate jellies made by boiling the juice of quince with honey. A second important innovation was the introduction from Asia of cane sugar, which unlike honey is nearly pure sugar, with no moisture that needs boiling off, and no strong flavor that competes with the flavor of the fruit. The Arab world was using cane sugar by the Middle Ages, and brought it to Europe in the 13th century, where it soon became the preferred sweetener for fruit preserves. However, jams and jellies didn't become common fare until the 19th century, when sugar had become cheap enough to use in large quant.i.ties.

Pectin Gels Fruit preserves are a kind of physical structure called a Fruit preserves are a kind of physical structure called a gel: gel: a mixture of water and other molecules that is solid because the other molecules bond together into a continuous, sponge-like network that traps the water in many separate little pockets. The key to creating a fruit gel is pectin, long chains of several hundred sugar-like subunits, which seems to have been designed to help form a highly concentrated, organized gel in plant cell walls (p. 265). When fruit is cut up and heated near the boil, the pectin chains are shaken loose from the cell walls and dissolve into the released cell fluids and any added water. They can't simply re-form their gel for a couple of reasons. Pectin molecules in water acc.u.mulate a negative electrical charge, so they repel each other rather than bond to each other; and they're now so diluted by water molecules that even if they did bond, they couldn't form a continuous network. They need help to find each other again. a mixture of water and other molecules that is solid because the other molecules bond together into a continuous, sponge-like network that traps the water in many separate little pockets. The key to creating a fruit gel is pectin, long chains of several hundred sugar-like subunits, which seems to have been designed to help form a highly concentrated, organized gel in plant cell walls (p. 265). When fruit is cut up and heated near the boil, the pectin chains are shaken loose from the cell walls and dissolve into the released cell fluids and any added water. They can't simply re-form their gel for a couple of reasons. Pectin molecules in water acc.u.mulate a negative electrical charge, so they repel each other rather than bond to each other; and they're now so diluted by water molecules that even if they did bond, they couldn't form a continuous network. They need help to find each other again.

The cook does three things to cooked fruit to bring pectin molecules back together into a continuous gel. First, he adds a large dose of sugar, whose molecules attract water molecules to themselves, thus pulling the water away from the pectin chains and leaving them more exposed to each other. Second, he boils the mixture of fruit and sugar to evaporate some of the water away and bring the pectin chains even closer together. Finally, he increases the acidity, which neutralizes the electrical charge and allows the aloof pectin chains to bond to each other into a gel. Food scientists have found that the optimal conditions for pectin gelation are a pH between 2.8 and 3.5 - about the acidity of orange juice, and 0.5% acid by weight - a pectin concentration of 0.5 to 1.0%, and a sugar concentration of 60 to 65%.

Preparing Preserves Preserve making begins with cooking the fruit to extract its pectin. Quince, apples, and citrus fruits are especially rich in pectin and often included to supplement other pectin-poor fruits, including most berries. The combination of heat and acid will eventually break pectin chains into pieces too small to form a network, so this preliminary cooking should be as brief and gentle as possible. (If a sparkling, clear jelly is desired, then the cooked fruit is gently strained to remove all solid particles of cell debris.) Then sugar is added, supplemental pectin if necessary, and the mixture rapidly brought to the boil to remove water and concentrate the other ingredients. The boiling is continued until the temperature of the mix reaches 217221F/103105C (at sea level; 2F/1C lower for every 500 ft/165 m elevation), which indicates that the sugar concentration has reached 65% (for the relationship between sugar content and boiling point, see p. 680). A fresher flavor results when this cooking is done at a gentle simmer in a wide pot with a large surface area for evaporation. (Industrial manufacturers cook the water out under a vacuum at much lower temperatures, 100140F/3860C, to maintain as much fresh flavor and color as possible.) Now supplemental acid is added (late in the process, to avoid breaking down the pectin chains), and the readiness of the mix is tested by placing a drop on a cold spoon or saucer to see whether it gels. Finally, the mix is poured into sterilized jars. The mix sets as it cools below about 180F/80C, but firms most rapidly at 86F/30C and continues to get firmer for some days or weeks. Preserve making begins with cooking the fruit to extract its pectin. Quince, apples, and citrus fruits are especially rich in pectin and often included to supplement other pectin-poor fruits, including most berries. The combination of heat and acid will eventually break pectin chains into pieces too small to form a network, so this preliminary cooking should be as brief and gentle as possible. (If a sparkling, clear jelly is desired, then the cooked fruit is gently strained to remove all solid particles of cell debris.) Then sugar is added, supplemental pectin if necessary, and the mixture rapidly brought to the boil to remove water and concentrate the other ingredients. The boiling is continued until the temperature of the mix reaches 217221F/103105C (at sea level; 2F/1C lower for every 500 ft/165 m elevation), which indicates that the sugar concentration has reached 65% (for the relationship between sugar content and boiling point, see p. 680). A fresher flavor results when this cooking is done at a gentle simmer in a wide pot with a large surface area for evaporation. (Industrial manufacturers cook the water out under a vacuum at much lower temperatures, 100140F/3860C, to maintain as much fresh flavor and color as possible.) Now supplemental acid is added (late in the process, to avoid breaking down the pectin chains), and the readiness of the mix is tested by placing a drop on a cold spoon or saucer to see whether it gels. Finally, the mix is poured into sterilized jars. The mix sets as it cools below about 180F/80C, but firms most rapidly at 86F/30C and continues to get firmer for some days or weeks.

Two kinds of pectin gels. Left: Left: In ordinary fruit preserves, the cook causes pectin molecules to bond directly to each other and form a continuous meshwork by carefully adjusting acidity and sugar content. In ordinary fruit preserves, the cook causes pectin molecules to bond directly to each other and form a continuous meshwork by carefully adjusting acidity and sugar content. Right: Right: A modified form of pectin (low methoxy) can be bonded into a continuous meshwork by means of added calcium ions (the black dots), no matter what the sugar content. This is how low-sugar preserves are made. A modified form of pectin (low methoxy) can be bonded into a continuous meshwork by means of added calcium ions (the black dots), no matter what the sugar content. This is how low-sugar preserves are made.

The usual problem with preserve making is failure of the mix to set even at the proper boiling temperature and sugar concentration. This can be caused by three different factors: inadequate amounts of either acid or good-quality pectin, or prolonged cooking that damages the pectin. Failures can sometimes be rescued by the addition of a commercial liquid pectin preparation and/or cream of tartar or lemon juice, and a brief reboiling. Too much acid can cause weeping of fluid from an overfirm gel.

Uncooked and Unsweetened "Preserves" Modern preserve making has been transformed by the availability of concentrated pectin, extracted and purified from citrus and apple wastes, which can be added to any crushed fruit, cooked or not, to guarantee a firm gel. "Freezer jams" are made by loading up crushed fresh fruit with supplemental pectin and sugar, letting them sit for a day while the pectin molecules slowly form their network and form the gel, and then "preserving" them in the refrigerator or freezer (the uncooked fruit would otherwise soon be spoiled by sugar-tolerant molds and yeasts). Pectin is also used to make clear jelly candies and other confections. Modern preserve making has been transformed by the availability of concentrated pectin, extracted and purified from citrus and apple wastes, which can be added to any crushed fruit, cooked or not, to guarantee a firm gel. "Freezer jams" are made by loading up crushed fresh fruit with supplemental pectin and sugar, letting them sit for a day while the pectin molecules slowly form their network and form the gel, and then "preserving" them in the refrigerator or freezer (the uncooked fruit would otherwise soon be spoiled by sugar-tolerant molds and yeasts). Pectin is also used to make clear jelly candies and other confections.

Food chemists have developed several different versions of pectin for special commercial applications. The most notable of these is a pectin that sets without the need for any added sugar to pull water molecules away from the long pectin chains; instead, the chains bond to each other strongly by means of cross-linking calcium, which is added after the fruit and pectin mixture has been cooked. This pectin is what makes it possible to produce low-calorie "preserves" with artificial sweeteners.

Candied Fruits Candied fruits are small whole fruits or pieces that are impregnated with a saturated sugar syrup, then drained, dried, and stored at room temperature as separate pieces. Fruit cooked in a sugar syrup remains relatively firm and maintains its shape thanks to the interaction of sugar molecules with the cell-wall hemicelluloses and pectins. Candying can be a tedious process because it takes time for sugar to diffuse from the syrup evenly into the fruit. Typically the fruit is gently cooked to soften it and make its tissues more permeable, then soaked for several days at room temperature in a syrup that starts out at 1520% sugar, and is made more concentrated each day until it reaches 7074%. Candied fruits are small whole fruits or pieces that are impregnated with a saturated sugar syrup, then drained, dried, and stored at room temperature as separate pieces. Fruit cooked in a sugar syrup remains relatively firm and maintains its shape thanks to the interaction of sugar molecules with the cell-wall hemicelluloses and pectins. Candying can be a tedious process because it takes time for sugar to diffuse from the syrup evenly into the fruit. Typically the fruit is gently cooked to soften it and make its tissues more permeable, then soaked for several days at room temperature in a syrup that starts out at 1520% sugar, and is made more concentrated each day until it reaches 7074%.

Canning Canning was a cause for wonder when it was invented by Nicolas Appert around 1810: contemporaries said that it preserved fruits and vegetables almost as if fresh! True, it preserves them without the desiccated texture of drying, the salt and sourness of fermentation, or the sweetness of sugar preserves; but there's no mistaking that canned foods have been cooked. Canning is essentially the heating of food that has been isolated in hermetically sealed containers. The heat deactivates plant enzymes and destroys harmful microbes, and the tight seal prevents recontamination by microbes in the environment. The food can then be stored at room temperature without spoiling.

The arch villain of the canning process is the bacterium Clostridium botulinum, Clostridium botulinum, which thrives in low-acid, airless conditions - oxygen is toxic to it - and produces a deadly nerve toxin. The botulism toxin is easily destroyed by boiling, but the dormant bacterial spores are very hardy and can survive prolonged boiling. Unless they are killed by the extreme condition of higher-than-boiling temperatures (which require a pressure cooker), the spores will proliferate into active bacteria when the can cools down, and the toxin will acc.u.mulate. One precautionary measure is to boil any canned produce after opening to destroy any toxin that may be there. But all suspect cans, especially those bulging from the pressure of gases produced by bacterial growth, should be discarded. which thrives in low-acid, airless conditions - oxygen is toxic to it - and produces a deadly nerve toxin. The botulism toxin is easily destroyed by boiling, but the dormant bacterial spores are very hardy and can survive prolonged boiling. Unless they are killed by the extreme condition of higher-than-boiling temperatures (which require a pressure cooker), the spores will proliferate into active bacteria when the can cools down, and the toxin will acc.u.mulate. One precautionary measure is to boil any canned produce after opening to destroy any toxin that may be there. But all suspect cans, especially those bulging from the pressure of gases produced by bacterial growth, should be discarded.

The low pH (high acidity) of tomatoes and many common fruits inhibits the growth of botulism bacteria, so these foods require the least severe canning treatment, usually about 30 minutes in a bath of boiling water to heat the contents to 185195F/8590C. Most vegetables, however, are only slightly acid, with a pH of 5 or 6, and are much more vulnerable to bacteria and molds. They're typically heated in a pressure cooker at 240F/116C for 30 to 90 minutes.

Chapter 6.

A Survey of Common Vegetables

Roots and Tubers PotatoesSweet PotatoesTropical Roots and TubersThe Carrot Family: Carrots, Parsnips, and OthersThe Lettuce Family: Sunchoke, Salsify, Scorzonera, BurdockOther Common Roots and Tubers Lower Stems and Bulbs: Beet, Turnip, Radish, Onion, and Others BeetsCelery RootThe Cabbage Family: Turnip, RadishThe Onion Family: Onions, Garlic, Leeks Stems and Stalks: Asparagus, Celery, and Others AsparagusThe Carrot Family: Celery and FennelThe Cabbage Family: Kohlrabi and RutabagaTropical Stems: Bamboo Shoots and Hearts of PalmOther Stem and Stalk Vegetables Leaves: Lettuces, Cabbages, and Others The Lettuce Family: Lettuces, Chicories, Dandelion GreensThe Cabbage Family: Cabbage, Kale, Brussels Sprouts, and OthersSpinach and ChardMiscellaneous Leafy Greens Flowers: Artichokes, Broccoli, Cauliflower, and Others Flowers as FoodsArtichokesThe Cabbage Family: Broccoli, Cauliflower, Romanesco Fruits Used as Vegetables The Nightshade Family: Tomato, Capsic.u.ms, Eggplant, and OthersThe Squash and Cuc.u.mber FamilyThe Bean Family: Fresh Beans and PeasOther Fruits Used as Vegetables Seaweeds Green, Red, and Brown AlgaeSeaweed Flavors Mushrooms, Truffles, and Relatives Creatures of Symbiosis and DecayThe Structure and Qualities of MushroomsThe Distinctive Flavors of MushroomsStoring and Handling MushroomsCooking MushroomsTrufflesHuitlacoche, or Corn s.m.u.tMycoprotein, or Quorn Chapter 5 described the general nature of plant foods and their behavior in the kitchen. This chapter and the next two survey some familiar vegetables, fruits, and flavorings. Because we eat hundreds of different plants, and countless varieties of them, these surveys can only be selective and sketchy. They're meant to highlight the distinctive qualities of these foods, to help the food lover appreciate those qualities more fully and make the best use of them.

These chapters give special attention to two features of our plant foods. One is family relationships, family relationships, which tell us which plants are related to each other, and conversely how varied a given species can be. Such information helps us make sense of similarities and differences among particular foods, and may suggest ideas for interesting combinations and themes. which tell us which plants are related to each other, and conversely how varied a given species can be. Such information helps us make sense of similarities and differences among particular foods, and may suggest ideas for interesting combinations and themes.

The second feature emphasized in the following pages is flavor chemistry. flavor chemistry. Fruits and vegetables, herbs and spices are the most complex foods we eat. If we know even a little bit about which substances create their flavor, then we become more attuned to how the flavor is built, and better able to perceive echoes and harmonies among different ingredients. Such perceptions enrich the experience of eating, and can help us become better cooks. All aromas come from particular volatile chemicals, and I sometimes name those chemicals to be as specific as possible about the qualities of a given food. The names may look foreign and incomprehensible, but they're simply names - and sometimes make more sense than the names of the foods they're in! Fruits and vegetables, herbs and spices are the most complex foods we eat. If we know even a little bit about which substances create their flavor, then we become more attuned to how the flavor is built, and better able to perceive echoes and harmonies among different ingredients. Such perceptions enrich the experience of eating, and can help us become better cooks. All aromas come from particular volatile chemicals, and I sometimes name those chemicals to be as specific as possible about the qualities of a given food. The names may look foreign and incomprehensible, but they're simply names - and sometimes make more sense than the names of the foods they're in!

This survey of vegetables begins underground, with the plant parts that sustain much of the earth's population. It then moves up the plant, from stem to leaf to flower and fruit, and finishes with water plants and those delicious nonplants, the mushrooms.

Roots and Tubers Potatoes, sweet potatoes, yams, ca.s.sava - these roots and tubers are staple foods for billions of people. They are subterranean organs in which plants store starch, large molecular aggregates of the sugars they create during photosynthesis. They are therefore a concentrated and long-lived package of nourishment for us as well. Some anthropologists theorize that roots and tubers may have helped fuel human evolution, when the climate of the African savanna cooled about 2 million years ago and fruits became scarce. Because tubers were plentiful and far more nutritious when cooked - raw starch granules resist our digestive enzymes, while gelated starch does not - they may have offered a significant advantage to early humans who learned to dig for them and roast them in the embers of a fire.

Though some underground vegetables are a third or more starch by weight, many others - carrots, turnips, beets - contain little or no starch. Because starch granules absorb moisture from their cells as they cook, starchy vegetables tend to have a dry, mealy texture, while nonstarchy vegetables remain moist and cohesive.

Food Words: Root, Radish, Tuber, Truffle Root, Radish, Tuber, TruffleOur word root root comes from an Indo-European word that meant both "root" and "branch." comes from an Indo-European word that meant both "root" and "branch." Radish Radish and and licorice licorice share that same ancestor. share that same ancestor. Tuber Tuber comes from an Indo-European (linguistic) root meaning "to swell," as many plant storage organs do. The same root gave us comes from an Indo-European (linguistic) root meaning "to swell," as many plant storage organs do. The same root gave us truffle, truffle, the swollen underground fungus, as well as the swollen underground fungus, as well as thigh, thumb, tumor, thigh, thumb, tumor, and and thousand. thousand.

Potatoes There are more than 200 species of potato, relatives of the tomato, chilli, and tobacco that are indigenous to moist, cool regions of Central and South America. Some were cultivated 8,000 years ago. Spanish explorers brought one species, Solanum tuberosum, Solanum tuberosum, from Peru or Colombia to Europe around 1570. Because it was hardy and easy to grow, the potato was inexpensive and the poor were its princ.i.p.al consumers. (An Irish peasant ate 510 pounds per day at the time of the 1845 blight.) It now leads all other vegetables in worldwide production. More potatoes are consumed in the United States than any other vegetable, around a third of a pound/150 gm per person per day. from Peru or Colombia to Europe around 1570. Because it was hardy and easy to grow, the potato was inexpensive and the poor were its princ.i.p.al consumers. (An Irish peasant ate 510 pounds per day at the time of the 1845 blight.) It now leads all other vegetables in worldwide production. More potatoes are consumed in the United States than any other vegetable, around a third of a pound/150 gm per person per day.

The potato is a tuber, the tip of an underground stem that swells with stored starch and water and bears primordial buds, the "eyes," that generate the stem and roots of a new plant. It is sometimes a little sweet, with a slight but characteristic bitterness, and has a mild earthy flavor from a compound (a pyrazine) produced by soil microbes, but also apparently within the tuber itself.

Harvest and Storage True "new" potatoes are immature tubers, harvested from green vines during the late spring and throughout the summer. They are moist and sweet, relatively low in starch, and perishable. Mature potatoes are harvested in the fall. The vines are killed by cutting or drying, and the tubers are left in the soil for several weeks to "cure" and toughen their skin. Potatoes can be stored in the dark for months, during which their flavor intensifies; slow enzyme action generates fatty, fruity, and flowery notes from cell-membrane lipids. The ideal storage temperature is 4550F/710C. At warmer temperatures they may sprout or decay, and at colder temperatures their metabolism shifts in a complicated way that results in the breakdown of some starch to sugars. Makers of potato chips must "recondition" cold-stored potatoes at room temperature for several weeks to reduce their levels of glucose and fructose, which otherwise cause the chips to brown too rapidly and develop a bitter taste. Internal black spots in potatoes are essentially bruises, formed when an impact during handling damages cells and causes the browning enzymes to create dark complexes of the amino acid tyrosine (alkaloid formation and therefore bitterness often rise also). True "new" potatoes are immature tubers, harvested from green vines during the late spring and throughout the summer. They are moist and sweet, relatively low in starch, and perishable. Mature potatoes are harvested in the fall. The vines are killed by cutting or drying, and the tubers are left in the soil for several weeks to "cure" and toughen their skin. Potatoes can be stored in the dark for months, during which their flavor intensifies; slow enzyme action generates fatty, fruity, and flowery notes from cell-membrane lipids. The ideal storage temperature is 4550F/710C. At warmer temperatures they may sprout or decay, and at colder temperatures their metabolism shifts in a complicated way that results in the breakdown of some starch to sugars. Makers of potato chips must "recondition" cold-stored potatoes at room temperature for several weeks to reduce their levels of glucose and fructose, which otherwise cause the chips to brown too rapidly and develop a bitter taste. Internal black spots in potatoes are essentially bruises, formed when an impact during handling damages cells and causes the browning enzymes to create dark complexes of the amino acid tyrosine (alkaloid formation and therefore bitterness often rise also).

Nutritional Qualities Potatoes are a good source of energy and vitamin C. Yellow-fleshed varieties owe their color to fat-soluble carotenoids (lutein, zeaxanthin), purple and blue ones to water-soluble and antioxidant anthocyanins. Potatoes are notable for containing significant levels of the toxic alkaloids solanine and chaconine, a hint of whose bitterness is part of their true flavor. Most commercial varieties contain 2 to 15 milligrams of solanine and chaconine per quarter-pound (100 grams) of potato. Progressively higher levels result in a distinctly bitter taste, a burning sensation in the throat, digestive and neurological problems, and even death. Stressful growing conditions and exposure to light can double or triple the normal levels. Because light also induces chlorophyll formation, a green cast to the surface is a sign of abnormally high alkaloid levels. Greened potatoes should either be peeled deeply or discarded, and strongly bitter potatoes should not be eaten. Potatoes are a good source of energy and vitamin C. Yellow-fleshed varieties owe their color to fat-soluble carotenoids (lutein, zeaxanthin), purple and blue ones to water-soluble and antioxidant anthocyanins. Potatoes are notable for containing significant levels of the toxic alkaloids solanine and chaconine, a hint of whose bitterness is part of their true flavor. Most commercial varieties contain 2 to 15 milligrams of solanine and chaconine per quarter-pound (100 grams) of potato. Progressively higher levels result in a distinctly bitter taste, a burning sensation in the throat, digestive and neurological problems, and even death. Stressful growing conditions and exposure to light can double or triple the normal levels. Because light also induces chlorophyll formation, a green cast to the surface is a sign of abnormally high alkaloid levels. Greened potatoes should either be peeled deeply or discarded, and strongly bitter potatoes should not be eaten.

Cooking Types and Behavior There are two general cooking categories of potato, called the "mealy" and the "waxy" for their textures when cooked. Mealy types (russets, blue and purple varieties, Russian and banana fingerlings) concentrate more dry starch in their cells, so they're denser than waxy types. When cooked, the cells tend to swell and separate from each other, producing a fine, dry, fluffy texture that works well in fried potatoes and in baked and mashed potatoes, which are moistened with b.u.t.ter or cream. In waxy types (true new potatoes and common U.S. red-and white-skinned varieties), neighboring cells cohere even when cooked, which gives them a solid, dense, moist texture, and holds them together in intact pieces for gratins, potato cakes, and salads. Both types can be made firmer and more coherent, less p.r.o.ne to the "sloughing" of outer layers when boiled, by treating them to the low-temperature precooking that strengthens cell walls (p. 283). There are two general cooking categories of potato, called the "mealy" and the "waxy" for their textures when cooked. Mealy types (russets, blue and purple varieties, Russian and banana fingerlings) concentrate more dry starch in their cells, so they're denser than waxy types. When cooked, the cells tend to swell and separate from each other, producing a fine, dry, fluffy texture that works well in fried potatoes and in baked and mashed potatoes, which are moistened with b.u.t.ter or cream. In waxy types (true new potatoes and common U.S. red-and white-skinned varieties), neighboring cells cohere even when cooked, which gives them a solid, dense, moist texture, and holds them together in intact pieces for gratins, potato cakes, and salads. Both types can be made firmer and more coherent, less p.r.o.ne to the "sloughing" of outer layers when boiled, by treating them to the low-temperature precooking that strengthens cell walls (p. 283).

Cooked potatoes sometimes develop a large internal region of bluish-gray discoloration. This "after-cooking darkening" is caused by the combination of iron ions, a phenolic substance (chlorogenic acid), and oxygen, which react to form a pigmented complex. This problem can be minimized in boiled potatoes by making the pH of the water distinctly acidic with cream of tartar or lemon juice after the potatoes are half-cooked.

The flavor of boiled potatoes is dominated by the intensified earthy and fatty, fruity, and flowery notes of the raw tuber. Baked potatoes develop another layer of flavor from the browning reactions (p.777), including malty and "sweet" aromas (methylbuta.n.a.l, methional). Leftover potatoes often suffer from a stale, cardboard-like flavor that develops over several days in the refrigerator, but within a few hours if the potatoes are kept hot for prolonged service. It turns out that the aromatic fragments of membrane lipids are temporarily stabilized by the tuber's antioxidant vitamin C; but with time the vitamin C is used up and the fragments become oxidized to a series of less pleasant aldehydes.