Image credit: Kham Tran via Wikimedia Commons [CC BY 3.0] (source)

What Is Mint?

After a restaurant meal, do you appreciate an after-dinner mint? Do you like mint-flavored toothpaste? Are you a fan of chocolate-mint ice cream or chocolate-mint cookies? What do you think of mint tea? Would you be willing to try an apple-mint smoothie? The concept of “mint” as a flavoring is quite familiar in our culture, and therefore the meaning seems fairly clear. But what exactly qualifies as “mint”? How many different kinds of plants can be called “mint”, and how do they differ from each other? Does “mint” as a flavoring come from just one of these plants, or several of them?

Mint as a garden plant has a very long history. The word “mint” comes from the ancient Greek word míntha — an indication of our long relationship with the plant. There are around 13 to 18 different species of mint — all in the botanical genus Mentha — but the exact number of species is a matter of debate, in part due to hybridization between the species. In addition to the recognized species, there are many recognized hybrids. Furthermore, for some of the more popular species, several different cultivated varieties (cultivars) have been developed, with different odors or other distinguishing characteristics.

The upshot is that if you consider growing mint as a garden plant, then you may encounter a confusingly large set of options — such as peppermint, spearmint, apple mint, orange mint, pineapple mint, banana mint, lemon mint, chocolate mint, and ginger mint. However, when the word “mint” is used without an adjective to describe a garden plant, then the plant is usually spearmint (Mentha spicata). This plant is not only popular in gardens, but is also an original source of mint flavoring.

The other most common mint for gardens — and commercial mint flavoring — is peppermint (Mentha x piperata). The “x” in the Latin name indicates that this plant arose as a hybrid between two species. One of the parent species is spearmint, and the other parent is water mint (Mentha aquatica). The resulting hybrid is sterile, which means that it won’t produce any seeds. However, peppermint — like the other mints — can easily spread by producing runners. Despite the fact that one of the parents is spearmint, peppermint smells and tastes quite different. If you grow both in your garden, then you can easily tell them apart from the odor. (They also look slightly different.)

The reason that spearmint and peppermint smell so different is because they produce different chemicals. The dominant chemical compound in spearmint oil is carvone. In contrast, the dominant compounds in peppermint oil are menthol and menthone. Commercial mint extract is often a blend of spearmint oil and peppermint oil, although one may be present in greater quantity than the other.

Three other types of mint are grown in commercially significant quantities:

  • Corn mint (Mentha arvensis) is also called Japanese peppermint or banana mint. Because the extract contains menthol and menthone, it is similar to peppermint oil.
  • Ginger mint (Mentha x gracilis), also called Scotch spearmint, is a sterile hybrid between spearmint and corn mint. The extract from ginger mint is similar to spearmint oil.
  • Apple mint (Mentha suaveolens) has both a fruity and minty flavor. One variety of apple mint is called pineapple mint.

As for the other popular mints with attractive names: The plant called chocolate mint is actually a variety of peppermint. Orange mint (also called bergamot mint or lemon mint) belongs to the species Mentha citrata. It contains a different set of compounds than the other mints mentioned above, giving it a strong odor of lavender. This species is used primarily in the perfume industry.

That covers all of the most popular varieties of mint. However, there are several other species and hybrids of Mentha that exist, some of which may be locally popular. For example, large apple mint (Mentha x villosa) is a hybrid of spearmint and apple mint that is popular in Cuba.

The word “mint” has a broader meaning when used in the phrase “the mint family”. This family, formally called Lamiaceae, contains approximately 235 genera, in addition to the genus Mentha. In all, the family contains about 7,000 species of plants. Except for the 13 to 18 species in the genus Mentha, none of them are true mints. However, they are all somewhat related, and they all share a family resemblance. A typical member of the mint family is an herbaceous (non-woody) plant with a square stem and opposite leaves. The flowers are bilaterally symmetric, and usually purple or white, or sometimes red. Most members of the family have distinctive odors to their foliage.

People have long enjoyed the odors and flavors provided by the mint family. As a result, a great number of our garden herbs are in that family, including basil, oregano, sage, rosemary, thyme, marjoram, and lavender. In each case, the plant produces a mix of chemical compounds that provide a distinctive odor and flavor. We call these compounds essential oils, because when extracted from the plant by steam or alcohol, the resulting oil smells very similar to the original plant. The range of odors is quite amazing. For example, there are many species and varieties of basil, with distinctive odors (and appearance). Sweet basil, also called Italian basil, contains a high concentration of eugenol, the same compound found in cloves. But if you grow Thai basil or African basil or lemon basil — or any of several other varieties of basil — then the odor will be somewhat different, depending upon the variety that you have chosen.

In addition to the garden herbs, there are many attractive wildflowers in the mint family — in both temperate and tropical climates — along with several common weeds. One of the most interesting genera in the family is Salvia — the sages. This genus, which contains around 900 species, includes a great number of plants with beautiful flowers or foliage, and the leaves often have a pleasant scent. Quite a few of these species are tropical — native to Mexico, Central America, or northern South America. The genus Salvia also includes the garden herb we call “sage”.

There is still one other popular meaning to the word “mint” — and that is to describe any odor or flavor that is reminiscent of mint, even if it comes from a plant that is completely unrelated to any of the mints. The best example is probably wintergreen (Gaultheria procumbens), an attractive little creeping plant with glossy green leaves and red berries. This plant is actually in the heath family, along with blueberries and azaleas. However, because oil of wintergreen has a minty odor and taste, it is often used in mint flavoring — although some people might describe the flavor as “medicinal” rather than minty.

The dominant chemical compound in oil of wintergreen is methyl salicylate. This compound is used to flavor toothpaste, chewing gum, soft drinks, Listerine, and many other products. In the past, this compound was commercially extracted from either wintergreen or sweet birch (Betula lenta). However, these days the compound is typically synthesized from salicylic acid, which is chemically related to aspirin, and can be found in several kinds of plants, such as willow bark.

So now we have discussed three different chemical compounds that we use for mint flavoring:

  • Carvone— the dominant compound in spearmint
  • Menthol (and the closely related menthone) — the dominant compound in peppermint
  • Methyl salicylate — the dominant compound in wintergreen

Carvone is fascinating because the molecule comes in two forms that are mirror images of each other — and yet the two versions smell and taste different to us. R-(–)-carvone is the form found in spearmint, while S-(–)-carvone, which has the odor of caraway, is the mirror-image form found in caraway seeds and dill.

Menthol is also fascinating, but for a different reason. Menthol stimulates the cold receptors in our skin without actually lowering the temperature of the skin. If you consume a product that contains menthol — such as certain cough drops or mint candies — then you feel this effect in your throat. If you see a product where the flavor is described as “cool mint”, then the product almost certainly contains menthol. Menthol is also used in products that are rubbed on the skin, such as Mentholatum and Vicks VapoRub, because the cooling sensation can be soothing.

Both of these compounds — carvone and menthol — can be synthesized from related compounds found in other kinds of plants. For example, carvone can be synthesized from limonene, a compound that is abundant in citrus peel. The commercial production of orange juice generates enormous amounts of orange peel as waste. As a result, it is generally cheaper to synthesize R-(–)-carvone from limonene than to extract it from spearmint or ginger mint. The demand for menthol is even greater, far exceeding the supply from natural sources such as peppermint and corn mint. Again the typical solution is to start with a different compound from another kind of plant — such as pinene from pine trees — going through several steps to convert it into menthol. Likewise, commercial methyl salicylate is usually synthesized from other compounds, rather than being extracted from wintergreen or other plants.

There is at least one other plant extract that some people may consider to be “minty”, and that is oil of eucalyptus. As the name suggests, the oil is derived from the leaves of eucalyptus trees or related plants. The oil is used as an ingredient in perfumes, cosmetics, mouthwash, antiseptics, ointments, toothpaste, and cough drops. The dominant compound in eucalyptus oil is usually eucalyptol. Eucalyptus oil, like oil of wintergreen, can be quite toxic if over-consumed.

So now we can answer the original question: What is mint? The best answer is that mint is any plant in the genus Mentha, which includes not only peppermint and spearmint (the two most common examples), but also several other closely related plants. We can also talk about the mint family, Lamiaceae, which contains a huge number of strongly scented plants, several of which we use as garden herbs — such as basil and sage. However, we don’t actually consider basil and sage to be types of mint, but simply members of the same family as mint. The word “mint” can also refer to a category of flavoring, traditionally extracted from peppermint and spearmint and related plants, but now often synthesized from cheaper types of plant extracts. A key feature of menthol, the dominant compound in peppermint oil, is that it triggers the cool receptors in the skin, resulting in a “cool mint” sensation. As a flavoring, the concept of “mint” has expanded to include wintergreen, a plant that is not actually a mint at all, but that has a minty odor. The upshot is that the word “mint” has several meanings, but all of these meanings are derived from the original meaning — the plants in the genus Mentha, especially peppermint and spearmint.

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