Garlic (Allium sativum) is a perennial plant in the family Alliaceae and genus Allium, closely related to the onion, shallot, and leek. It grows in the wild in areas where it has become naturalised, but is thought to have originally arisen in cultivation, probably descended from the species Allium longicuspis, which grows wild in south-western Asia. Garlic has been used throughout all of recorded history for both culinary and medicinal purposes.

The portion of the plant most often consumed is an underground storage structure called a head. A head of garlic is composed of a dozen or more discrete cloves, each of which is a botanical bulb, an underground structure comprised of thickened leaf bases. Each garlic clove may often be composed of just one leaf base, unlike onions, which almost always have multiple layers. The above-ground portions of the garlic plant are also sometimes consumed, particularly while immature and tender.

Garlic has a powerful pungent or "hot" flavor when raw, which mellows considerably when it is cooked. Raw or cooked, garlic is noted for its strong characteristic odor.

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Culinary use
Garlic is most often used as a seasoning or a condiment. When crushed or finely chopped it yields allicin, a powerful antibiotic and anti-fungal compound (phytoncide). It also contains alliin, ajoene, enzymes, vitamin B, minerals, and flavonoids.

Garlic is widely used in many forms of cooking for its strong flavor, which is considered to enhance many other flavors. Depending on the form of cooking and the desired result, the flavor is either mellow or intense. It is often paired with onion, tomato, and/or ginger.

In culinary preparation, it is necessary to remove the parchment-like skin from individual cloves before chopping. Lightly crushing the cloves with the ball of the hand or flat of a knife makes this job much easier. A common error made by novice cooks is to misinterpret the word "clove" as meaning the entire garlic head (naturally occurring cluster of cloves, depending on the species) rather than one of its segments, thereby wildly exaggerating the amount of garlic in a recipe. Aside from the bulbs, the shoots are often pickled in Russia and states of the Caucasus and eaten as an appetizer.

Garlic leaves are a popular vegetable in many parts of Asia. In particular Chinese, Vietnamese, and Cambodian cultures occasionally feature garlic leaves as ingredients. The leaves are cut fresh, cleaned and then stir-fried with eggs, meat, or other vegetables. The flavor is mildly reminiscent of garlic, and leaves a minimal scent on the breath of the consumer.

Fresh Garlic bulbs are also pickled in Chinese cuisine. The tender bulbs (before the skin has hardened) are pickled in a mixture of sugar, salt, and other spices. After a period of 3 to 6 weeks, the pickled garlic can be consumed. Very popular with South-east Asians, international connoisseurs can purchase them at Asian markets.

Often garlic and herbs are stored in cooking oil to create an oil that is infused with the flavors of the garlic and herbs used. This is done both commercially and at home. Care must be taken when storing garlic and herbs this way at home as there is a risk of botulism developing in the oxygen-free oil if the product is not stored properly. To reduce the risk of botulism, the oil containing the garlic must be refrigerated and used within one week. Commercial producers of garlic-in-oil use a combination of salts and/or acids to eliminate the risk of botulism in their products.

When eaten in quanity, garlic may be strongly evident in the diner's sweat and breath the following day. This is because garlic's strong smelling sulfur compounds are metabolized forming allyl methyl sulfide. Allyl methyl sulfide (AMS) cannot be digested and is passed into the blood. It is carried to the lungs and the skin where it is excreted. Since digestion takes several hours, and release of AMS several hours more, the effect of eating garlic may be present for a long time.

The well-known phenomenon of "garlic breath" is alleged to be alleviated by eating fresh parsley. This is, therefore, included in many garlic recipes, e.g. Pistou and Persillade. However, since garlic breath results mainly from digestive processes placing compounds such as AMS in the blood, and AMS is then released through the lungs over the course of many hours, eating parsley is at best a temporary fix. One way of accelerating the release of AMS from the body is the use of a sauna. Because of its strong odor, garlic is sometimes called the "stinking rose".

Hardneck garlic varieties feature a seedpod that grows atop a leafless stalk known as a "scape". Immature scapes are tender and edible. They are also known as "garlic spears", "stems", or "tops". Scapes generally have a milder taste than cloves. They are often used in stir frying or prepared like asparagus.

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Medicinal use
Some scientific research indicates that garlic can have health benefits, such as preventing and fighting common cold, diminishment of platelet aggregation; a meta-analysis showing significant (8% compared to placebo) lowering of Low density lipoprotein carrying cholesterol (LDL-C); treatment of hyperlipidaemia; the significant inhibition of atherosclerosis via the use of aged garlic extract Kyolic; and the protective nature of chronic garlic intake on elastic properties of aorta in the elderly. However more recent studies and meta-analyses have challenged the real extent to which garlic can improve cholesterol levels. Regular and prolonged use of therapeutic amounts of aged garlic extracts lower blood homocysteine levels, and has shown to prevent some complications of diabetes mellitus. It may have some cancer-fighting properties because it is high in diallyl sulphide (DADs), believed to be an anticarcinogen. Decocted garlic extracts that are left to set overnight are very effective in healing wounds. In 1858, Louis Pasteur observed garlic's antibacterial activity, and it was used as an antiseptic to prevent gangrene during World War I and World War II.

In modern naturopathy, garlic is used as a treatment for intestinal worms and other intestinal parasites, both orally and as an anal suppository.

Garlic cloves continue to be used by aficionados as a remedy for infections (especially chest problems), digestive disorders, and fungal infections such as thrush. They are claimed to be an effective long-term remedy for cardiovascular problems reducing excessive blood cholesterol levels, atherosclerosis, the risk of thrombosis, and hypertension but these claims are disputed, as there has been no clinical trial that has demonstrated any such benefits. Whole cloves used as vaginal suppositories are sometimes used as a home remedy for Candidiasis (yeast infections). Garlic is also alleged to help regulate blood sugar levels, and so can be helpful in late-onset diabetes, though people taking insulin should not consume medicinal amounts of garlic without consulting a physician. In such applications, garlic must be fresh and uncooked, or the allicin will be lost.

Garlic supplementation in rats along with a high protein diet has been shown to boost testosterone levels

Dietary supplements in pill form, as are commonly available, claim to possess the medicinal benefits of garlic, without (in the words of one manufacturer) "the unsocial qualities associated with fresh garlic cloves".

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History

From the earliest times garlic has been used as an article of diet. It is very widely used in Lebanese cuisine. Many Lebanese salads contain a garlic sauce. It formed part of the food of the Israelites in Egypt (Numb. xi. 5) and of the labourers employed by Khufu in constructing the pyramid. Garlic is still grown in Egypt, but the Syrian variety is the kind most esteemed now (see Rawlinson's Herodotus, 2.125).

It was consumed by the ancient Greek and Roman soldiers, sailors and rural classes (cf. Virg. Ed. ii. II), and, as Pliny tells us (N.H. xix. 32), by the African peasantry. Galen eulogizes it as the "rustic's theriac" (cure-all) (see F Adams's Paulus Aegineta, p. 99), and Alexander Neckam, a writer of the 12th century (see Wright's edition of his works, p. 473, 1863), recommends it as a palliative of the heat of the sun in field labor.

Pliny the Elder, in his Natural History, (N.H. xx. 23) gives an exceedingly long list of scenarios in which it was considered beneficial. Dr. T. Sydenham valued it as an application in confluent smallpox, and, says Cullen (Mat. Med. ii. p. 174, 1789), found some dropsies cured by it alone. Early in the 20th century, it was sometimes used in the treatment of pulmonary tuberculosis or phthisis.

Garlic was rare in traditional English cuisine (though it is said to have been grown in England before 1548), and has been a much more common ingredient in Mediterranean Europe. Garlic was placed by the ancient Greeks on the piles of stones at cross-roads, as a supper for Hecate (Theophrastus, Characters, The Superstitious Man); and according to Pliny, garlic and onions were invoked as deities by the Egyptians at the taking of oaths. The inhabitants of Pelusium in lower Egypt, who worshipped the onion, are said to have had an aversion to both onions and garlic as food.

To prevent the plant from running to leaf, Pliny (Nat. Hist. xix. 34) advised bending the stalk downward and covering with earth; seeding, he observes, may be prevented by twisting the stalk (by "seeding", he most likely means the development of small, less potent bulbs).

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Superstition and mythology
Garlic has been seen as a force for both good and evil. A Christian myth says that after Satan left the Garden of Eden, garlic arose in his left footprint, and onion in the right. Even in Europe, though, many cultures have turned to garlic as a protective force or white magic, perhaps because of its reputation as a powerful preventative medicine. Central European folk beliefs considered garlic a powerful ward against demons, werewolves, and vampires. To ward off vampires, garlic could be worn on one's person, hung in windows, or rubbed on chimneys and keyholes.

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Classification
Classification of culinary garlic can be complex, with numerous cultivars being grown. The broadest division is into "hardneck" and "softneck" types; very broadly speaking, hardnecks have more intense flavours (which are more closely related to their wild ancestor) but lesser storage capabilities, while conversely softnecks are excellent "keepers" but often milder (those are broad-brush simplifications with numerous exceptions and half-exceptions). Within those two types, there are usually felt to be three subdivisions of hardnecks and two of softnecks.

The "wild garlic", "crow garlic" and "field garlic" of Britain are the species Allium ursinum, A. vineale and A. oleraceum, respectively. In North America, "wild garlic" or "crow garlic" is Allium vineale, and along with "wild onion" (also known as "meadow garlic" or "wild garlic") Allium canadensis, are common weeds in fields. Elephant garlic is a variant of the leek species, A. ampeloprasum, and is larger and milder than true garlic.

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Preservation
The types differ not only in culinary qualities, but in storage potential. Under good storage conditions, which are not hard to achieve (room temperature and medium to low humidity), one can hope for these results:

• Asiatic, Turban and Porcelain types: a few months
• Rocambole and Purple Stripe types: 6 to 8 months
• Artichoke types: 8 to 10 months
• Silverskin (including Creole) types: up to a full year

Rocamboles, however, have a tendency to dehydrate in storage under dry conditions (less than about 50% humidity).

The bulbs are best preserved hung in a dry place. If of fair size, four to six of them weigh about 500 g (1 lb). Also, it is very important to keep them out of the sun. A dark corner of the room is best.

Do not store garlic in oil at room temperature. See Caution, below.

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Caution
Cases of botulism have been caused by consuming garlic-in-oil preparations. It is important to add acid when creating these mixtures and to keep them refrigerated to retard bacterial growth.

While culinary quantities are considered safe during pregnancy and breastfeeding, extremely large quantities of garlic and garlic supplements have been linked with a raised risk of bleeding. Some breastfeeding mothers have found their babies slow to feed and have noted a garlic odour coming from their baby when they have consumed garlic.

The side effects of long-term garlic supplementation, if any exist, are largely unknown and no FDA-approved study has been performed. However, garlic has been consumed for several thousand years without any adverse long-term effects, suggesting that modest quantities of garlic pose, at worst, minimal risks to normal individuals.

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Biology and chemistry
Because of its wide cultivation, the origins of garlic are not fully certain. It is related to onions and lilies, and cultivated in the same manner as the shallot. The domesticated garlic plant does not produce seeds, but is grown from bulbs. These bulbs are the part of the plant most commonly eaten, though some cooks also use the early spring shoots.

A garlic head is generally four to eight centimeters in diameter, white to pinkish or purple, and is composed of numerous (8 - 25) discrete bulbs. The foliage comprises a central stem 25 - 100 cm tall, with flat or keeled (but not tubular) leaves 30 - 60 cm long and 2 - 3 cm broad. The flowers are produced in a small cluster at the top of the stem, often together with several bulblets, and surrounded by a papery basal spathe; each flower is white, pink or purple, with six tepals 3 - 5 millimetres long. The flowers are commonly abortive and rarely produce any seeds.

The garlic plant has long, narrow, flat, obscurely keeled leaves. The head (compound bulb) has a flaky, mostly white outer layers of skin like that of an onion. Inside are 8-25 cloves, or smaller bulbs. From these, new bulbs can be procured by planting out in late winter or early spring.

The percentage composition of the bulbs is given by E. Solly (Trans. Hon. Soc. Loud., new ser., iii. p. 60) as water 84.09%, organic matter 13.38%, and inorganic matter 1.53% - that of the leaves being water 87.14%, organic matter 11.27% and inorganic matter 1.59%.

Like other members of the onion family, garlic actually creates the chemicals that give it its sharp flavor when the plant's cells are damaged. When a cell of a garlic clove is broken by chopping, chewing, or crushing, enzymes stored in cell vacuoles trigger the breakdown of several sulfur-containing compounds stored in the cell fluids. The resultant compounds are responsible for the sharp or hot taste and strong smell of garlic. Some of the compounds are unstable and continue to evolve over time. Among the members of the onion family, garlic has by far the highest concentrations of initial reaction products, making garlic much more potent than onions, shallots, or leeks. Although people have come to enjoy the taste of garlic, these compounds are believed to have evolved as a defensive mechanism, deterring animals like birds, insects, and worms from eating the plant.

A large number of sulfur compounds contribute to the smell and taste of garlic. Diallyl disulfide is believed to be an important odor component. Allicin has been found to be the compound most responsible for the spiciness of raw garlic. This chemical opens thermoTRP (transient receptor potential) channels that are responsible for the burning sense of heat in foods. The process of cooking garlic removes allicin, thus mellowing its spiciness.