Peppermint Oil

#### Peppermint Oil. One of the largest and most important of all the essential oils is hardly used at all in perfumery. If we add “mint” oil production (see **Mentha Arvensis Oil) **to that of peppermint, the total world production easily surpasses 5,000 metric tons, a fact which almost makes this oil type the third largest (after turpentine and pine oils) and equal to that of citronella and camphor oils. In respect to value, the peppermint + mint oils exceed the two latter oil types by far (see tables in rear of book). True *peppermint** *oil is steam distilled from the partially dried herb of **Mentha**** ****Piperita**** **which is a hybrid from three other species of **Mentha**, all natives of southern Europe. The peppermint plant was brought to the U.S.A. early in the 19th century, and these plants were the foundation of what are today the largest peppermint growing centers in the world: first, the northeastern United States, now practically abandoned except for experimental stations, then the midwestern states of Michigan, Indiana, Ohio and Wisconsin, all decreasing their production; the fareastern states of Oregon and Washington are now the main producers of American peppermint oil. The plant is also cultivated in Brazil, Argentina, France, Italy, Morocco, Poland, U.S.S.R., Bulgaria, Holland, Spain, Yugoslavia, Hungary, Germany, England, Rumania, India, Australia and several other countries. The U.S.S.R., Bulgaria, Italy and Morocco are the only countries that produce either very large quantities or sufficient amounts to make significant exports of the oil. The production of peppermint oil and all the problems connected with its production are so comprehensively described in literature that the author finds it superfluous to include such details here. It will suffice to say that the plants are all cultivated, and are distilled when fully mature, i.e. in full bloom, at the early blooming rather than at the end of blooming. It is particularly important in the U.S.A. in order to control the content of **Menthofuran**, a characteristic but not highly appreciated ingredient in true peppermint oil. This is a typical *physiological** *problem as met with frequently in the production of essential oils. Menthofuran is a derivative of furan with a certain chemical relationship to coumaron. The essential oil, steam distilled from the rapidly dried herb, is known as “natural peppermint oil”. For most flavoring purposes, this oil is “rectified”, either by steam distillation or by vacuum distillation. The former method is definitely preferable, provided the distillation is carried out with live steam at atmospheric pressure and under possible fractionation in a column with a minimum of holdup (perforated plate type column). Other commercial oils are labelled “triple rectified” or the like, and may have been further fractionated in order to remove all unpleasantly smelling or tasting fractions, bitter menthone, weedy foreruns, resinous-oily residues, etc. **Natural**** ****Peppermint**** ****Oil**** **is a pale yellow or pale olive colored liquid of fresh, strong, somewhat grassy-minty odor with a deep balsamic-sweet undertone and a sweet, clean dryout note. The grassy topnote may disappear or fade after proper ageing of the oil (polymerization of the lower aldehydes, etc.). Even the odor gives an impression of coolness, often due to the psychological effect of associating the known flavor with the impression of the odor. Peppermint odor and flavor are well known by practically everybody who brushes his teeth, eats candy, chews gum, uses mouth sprays or gargles, etc. The flavor of the oil appears strong and cooling, but the cooling effect masks some of the delicate, sweet-balsamic undertones of the oil. This is most unfortunate, but it is possible to recall these undertones at certain lower levels of dosage. Below the concentration of one part in 20,000 (or 5,00 mg%), the cooling effect fades away, while the actual *flavor *of the oil remains perceptible at about five to ten times this dilution, strongly dependent upon the medium to be flavored, the sugar concentration, temperature, solvent type, etc. The **Minimum Perceptible **of a good average grade rectified peppermint oil under the experimental circumstances (as outlined under **Flavors **in Part One of this work) is about 0.10 to 0.30 mg%. The coolness is a mouth feel, a physiological effect, not truly a flavor or an odor. But the coolness is the primary reason for the extensive use of peppermint oil in flavors. Accordingly, the average use level of the oil is usually on the high side of the above figure for minimum perceptible of cooling effect (i.e. higher than *5 *mg%). The concentration in certain types of peppermint candy, in chewing gum and in toothpaste is 100 times higher or more (up to 1.00 percent), a fact which gives a good idea of the highly flexible dosage of this oil. **Rectified **or “redistilled” peppermint oils are water-white or almost colorless. Their flavor is free from “weedy” topnotes and harsh-resinous or oily residue notes. The oil is more easily soluble in diluted alcohol, and its keeping qualities are superior to those of the natural oil. The loss by rectification amounts to 3 or 4% up to 20%, depending upon the selection of fractions and the type of distillation performed. One advantage of vacuum distillation is that the oil is freed from the water. Even a perfectly clear natural peppermint oil may contain over 1% of water which is harmful to the flavor and chemical composition of the oil, e.g. by hydrolysis or by supporting fungus growth or decay. **Mitcham**** ****Peppermint**** ****Oil**** **is distilled in England from a Mentha species which is a parent of the American peppermints. The English oil, also known as “black Mitcham oil” is known for its unusually high content of menthylesters (gives excellent body and sweetness to the flavor, and indirectly subdues the paralyzing effect of the “cool” menthol), and their modest content of the bitter tasting ketone, **Menthone**. The cool effect of this oil is perceptible only beyond the concentration of 1.00 to 2.00 mg%, while the **Minimum**** ****Perceptible**** **is about 0.10 to 0.30 mg%. The English Mitcham plant has now been introduced into France, Italy, Bulgaria, Argentina and numerous other countries. However, in no country other than England is the typical old- fashioned Mitcham peppermint oil produced. The English production is very small, and does not cover even part of the United Kingdom consumption, but the Mitcham oil is so expensive that it limits itself to use in high-class candies, etc. **Peppermint**** ****Oil**** **is very frequently adulterated outside the U.S.A. The most common adulterant is the essential oil of mentha arvensis (see **Mentha Arvensis Oil). **Modest additions of this oil to true peppermint oil can hardly be detected in chemical analysis, but an organoleptical test by experienced flavorists will usually reveal the fraud. Modern instrumental analysis will, in the hands of expert analysts, offer an efficient tool to provide printed proof of such fraud. Menthyl acetate prepared from racemic (liquid) menthol, is also used in the adulteration of peppermint oil. Fractions of peppermint oil (foreruns) are used to introduce the positive menthofuran test (see **Mentha Arvensis Oil); **fractions of mentha arvensis oil are used as diluents, and the cruder adulterations include the use of benzyl alcohol, triacetin, nopol, 2-cyclohexyl-cyclohexanone, tri- methyl cyclohexanol, etc. **Peppermint**** ****Oil**** **is occasionally used in perfumes, e.g. in lavender colognes (lift and freshness), fougères, geranium bases, etc. for its generally “lifting” effects at low concentration. Menthol is used for similar purposes at concentrations of 0.5 up to 2 or 3 percent in certain perfume bases. The peppermint oil has also been used for its cooling effect in certain cosmetics, lipsticks, lipstick perfumes, etc. face creams, shaving creams, hair lotions, etc., but it has greatly been replaced with natural or synthetic menthol for these purposes. In flavors, it is definitely not possible to replace peppermint oil with plain menthol, and there is no indication of peppermint oil losing its popularity as a world-wide accepted everyday flavor material in spite of its comparatively high cost.