Mint

A cool leaf with two different smells

Mint is the fresh leaf of plants in the genus Mentha, a group of strongly scented perennial herbs in the mint family, Lamiaceae. The plants stand 10 to 120 centimetres tall and have square stems, leaves in opposite pairs with serrated edges, and small white, pink or purple flowers packed in rings along the stem. Leaf colour runs from dark green to purple-tinged or pale yellow-green. Mint spreads by runners, which is why it is the herb that takes over a garden bed.

How many mints there are depends on who is counting. A conservative revision recognises 18 species and 11 hybrid species, Kew's Plants of the World Online lists 24 species and 15 hybrids, and more than 3,000 names have been published for the genus. Mints cross freely wherever two of them grow together, so much of what is sold as a species is a hybrid or a clone kept going by cuttings.

For a cook the genus divides into two smells. Peppermint and the corn mints carry menthol and menthone, which give the sharp, cooling, almost medicinal note of mint sweets and toothpaste. Spearmint carries carvone and smells sweeter, greener and warmer. Spearmint is the mint most kitchens mean when a recipe says only "mint": it is the one in mint sauce, in Moroccan tea, in chutney and in a bowl of yoghurt with cucumber. Peppermint is the mint of sweets, liqueurs and tea bags.

The name and the first records

The word mint comes from Latin mentha, which comes from Greek míntha and, before that, a Linear B word written mi-ta. In Greek myth Minthe was a nymph loved by Hades; in the version in Ovid, Persephone or Demeter turned her into the plant, or Hades caused the fragrant plant to grow from her dust. The myth fixes the plant in the Greek world, and a mountain called Mount Minthe near Pylos is named in this tradition. The Persian word pudna, for pennyroyal, gave rise to the Indo-Aryan pudīna, the name by which mint is known in India.

Greek and Roman herbals name several mints, including works by Hippocrates, Dioscorides, Galen, Cato, Ovid and Pliny the Elder. The oldest surviving illustrations of mint species are in the Vienna Dioscorides, a manuscript prepared in Constantinople in 512 CE for the princess Juliana Anicia. The Roman cookbook attributed to Apicius includes a mint sauce for roast lamb or kid. Spearmint is traditionally said to have reached England with the Romans by the fifth century, but that account does not date the beginning of its cultivation there.

Arabic- and Persian-language medical writing carried Greek herb traditions forward and added new uses. Majusi, writing in 994 CE, prescribed raw mint mixed with vinegar for fainting and vomiting; Ibn Sina, who died in 1037, recommended its sherbet. Sekanjabin is a honey-and-vinegar drink flavoured with mint. John Gerard's 1597 Herbal recommends spearmint for watering eyes and for wasp and bee stings. English household books later record mint sauce made with chopped mint, sugar and vinegar; by the mid-eighteenth century it was established with lamb. In 1816, French cook Louis Eustache Ude noted that England served mint sauce with sugar and vinegar in a sauceboat, while France used maître d'hôtel sauce.

How peppermint was made and how mint became a crop

Peppermint is a very young plant by comparison. It is a hybrid of watermint, Mentha aquatica, and spearmint, Mentha spicata, and it is sterile, so every plant is a clone. John Ray published it in 1696 from a find in Hertfordshire credited to a Dr Eales, and it entered the London Pharmacopoeia in 1721. Linnaeus gave it the name Mentha × piperita in 1753.

Growing mint for oil became an industry in England in the 1750s. By 1796 about 40 hectares of peppermint were grown near Mitcham, south of London, then harvested and carried to London for distillation. Over the next twenty years the district spread to ten townships. Mitcham peppermint travelled with settlers to North America; commercial peppermint was being raised in Massachusetts by 1812, and nine distilleries worked in New York by 1830. In 1853 Albert M. Todd brought roots of Black Mitcham to Michigan. By 1915 Todd was growing several hundred acres of Scotch spearmint, a cross of corn mint and spearmint, which out-yielded native spearmint. Mitcham cultivation ended by 1940. A review of Japanese mint history reports that corn mint (Mentha arvensis) was distilled for menthol in Japan, where a menthol eye medicine appears in the oldest surviving Japanese medical text of 984 CE; Japan began exporting menthol in 1873.

Today most mint oil comes from China, India and Japan, where corn mint is distilled for menthol, and the United States mint oil trade, at its peak in 2011 near 3,175 tonnes of peppermint oil and about 1,000 tonnes of spearmint oil, has declined as Asian menthol grew. Counted as plant production rather than oil, the leading peppermint producers reporting to the Food and Agriculture Organization in 2018 were Morocco, Argentina, Mexico, Bulgaria and Spain, and a later table gives Morocco 27,784 tonnes in 2022 out of a world total of 35,547. The living genetic stock is kept in a collection at Corvallis, Oregon, which holds about 450 clones of 34 mint types.

What makes the smell

Mint's scent is essential oil held in small glands on the leaf surface. The oils are mixtures of terpenes and the reported composition varies enormously with species, chemotype, growing site, soil, the stage the plant has reached when cut, and even whether the leaf was analysed fresh or dried. A review of the published analyses found one species of watermint, Mentha aquatica, with 26 distinct chemical types, and spearmint oils in which a single compound, piperitone oxide, made up 36 to 95 per cent of the oil.

Two families of compound define the cook's mints. In peppermint the oil is dominated by menthol, a cooling alcohol, with menthone beside it; one analysis gave menthol 41 per cent and menthone 23 per cent, and the dried leaf yields 0.3 to 0.4 per cent volatile oil. The proportions swing widely: a commercial peppermint oil bought in New Delhi measured 19 per cent menthol, while corn mint oils analysed in China and Brazil ran from 29 to 81 per cent, which is why the same word covers a mild leaf and a harsh one. In spearmint the signature compound is (−)-carvone, at 40 to nearly 68 per cent of the oil in different studies, accompanied by limonene, which adds a citrus note, and 1,8-cineole. Spearmint carries almost no menthol, which is why it tastes warm and sweet instead of icy. Pennyroyal and Corsican mint are different again, with pulegone as their main compound.

Warmth and light matter. Peppermint wants long days with warm to hot conditions and cool nights to strike the right balance of oil compounds, and its menthol content is higher at flowering than at budding. Spearmint leaves lose their aromatic appeal once the plant has flowered.

What mint does in fermented foods

Mint seasons foods that may themselves be fermented, including yoghurt sauces and chutneys. It does not act as a starter in the preparations described here. Its fresh, cool aroma can complement sourness and salt, but the herb is present for flavour.

Laboratory studies find antimicrobial activity for some mint oils, but effects in food depend on the food matrix. Fat, protein, salt and water activity can limit the activity of essential oils, and their results in culture cannot be carried directly over to a recipe. Menthol, a major compound in peppermint, is a weaker antibacterial than phenolic compounds such as thymol and carvacrol.

A study tested peppermint oil in tzatziki, a cucumber-and-yoghurt dip: concentrations from 0.5 to 2.0 per cent eliminated added Salmonella enteritidis there, while the effect was not seen in pâté. These are oil concentrations tested in a study, not ordinary amounts of fresh leaf. The results do not show that mint leaves make a yoghurt sauce safe or preserved.

Dried mint is the dehydrated leaf form. It is sold separately from fresh mint and has a different texture and aroma.

The mints you will meet

Spearmint, Mentha spicata, native from Ireland to southern China, is the common kitchen mint. It comes as plain garden mint, as a crinkle-leaved form sold as Crispa or Moroccan mint, as Tashkent and Spanish selections, and as the tea mint grown in the mountains of Morocco. Peppermint, M. × piperita, is the cooling hybrid, with forms such as Black Mitcham and Chocolate mint. Scotch spearmint, M. × gracilis, a cross with corn mint, is called ginger mint, and Cuban or mojito mint is M. × villosa, a cross of spearmint with round-leaved mint.

Apple mint, Mentha suaveolens, and its hybrid false apple mint are grown for culinary and ornamental use. Corn mint, M. arvensis, is also called field mint and is cultivated for menthol in parts of Asia. Recipe and market names such as mint, pudina, spearmint and peppermint can refer to different Mentha plants or products. Identify the species or form from the label or source when it matters; taste alone does not establish a plant's identity.

Using, choosing and keeping fresh mint

Choose bunches with green, unwilted leaves and sound stems. The University of Illinois Extension describes keeping cut stems in water for three to seven days and refrigerating leaves in a plastic bag for about a week. Colorado State University Extension advises against refrigerating or freezing mint and recommends hanging it to dry. These sources give different storage advice. Neither establishes a universal storage duration for every bunch or cultivar, so use fresh mint promptly and follow the conditions that suit the product and purpose.

For drying, cut the mint just as the flowers begin to open; for fresh use, pick as needed, because frequent cutting produces new growth and the new growth has the most flavour. Dried leaves are used in cooking and tea.

Mint can cause allergic reactions in some people, from oral tingling and heartburn to contact dermatitis, and, rarely, anaphylaxis. The strong peppermint oil should be kept away from the faces of small children.

Where mint goes on the plate

Mint is used in British mint sauce for roast lamb, in mint jelly in the United States, in Syrian limonana, and in Indian curries and green chutneys. Mint is also a necessary leaf in Tuareg tea, and it is used with lamb in Middle Eastern cooking. Cocktails such as the mint julep and mojito use it as well. These examples span different species, preparations and serving contexts; a recipe that says only “mint” may not identify the cultivar.

Mint often appears with sour ingredients: English mint sauce combines the leaf with vinegar, while chutneys and raita may pair it with citrus, yoghurt or tamarind. Sekanjabin combines mint with honey and vinegar. The form and proportions vary by recipe, and those fresh preparations should not be treated as preserved solely because they contain an acidic ingredient.

Growing mint

Mint grows best in cool, moist soil rich in organic matter, with a pH from 6 to 7.5, in full sun to partial shade, and it grows almost anywhere in a temperate climate. It spreads by runners above and below ground, so gardeners plant it in a pot or a bottomless container, though the roots can escape the latter. Peppermint is sterile and propagated only from cuttings of runners; spearmint and corn mint do set viable seed but are normally grown from cuttings too, and one hectare of well-grown stock can supply seven to ten hectares of new planting. Divide plants every three to four years and cut the flower spikes as they appear to keep the leaf flavour. Frequent cutting makes new growth, which is the best-tasting. The leaf is best picked in the morning after the dew dries, when the oil content is highest.

The great disease of the mint industry is verticillium wilt, caused by the soil fungus Verticillium dahliae. The old peppermint cultivar Black Mitcham is very susceptible and also sterile, which has made it hard to improve by breeding; resistant cultivars such as Todd's Mitcham and Roberts Mitcham were developed by radiation and mutation breeding.

Open points

The origin of Black Mitcham peppermint has not been established. A proposed parentage for spearmint involves Mentha longifolia and M. suaveolens, and peppermint is a hybrid with watermint, but the reviewed sources do not establish when or where these plants first arose. A review mentions peppermint in connection with the Ebers Papyrus, a claim that is uncertain because peppermint was formally described much later. Mount Minthe near Pylos has been proposed as a possible location associated with triploid spearmint, but this does not establish a birthplace.