Source: Perfumer & Flavorist, 2009. A preliminary report on the world production of some selected essential oils and countries, Vol. 34, January 2009.
EO production worldwide quantities figures 2008 (partly esteemed)
EO production worldwide quantities figures 2008 (partly esteemed)
FIGURE 4.1 Production countries and essential oil production worldwide (2008). (Adapted from Perfumer & Flavorist, 2009. A preliminary report on the world production of some selected essential oils and countries, Vol. 34, January 2009.)
FIGURE 4.1 Production countries and essential oil production worldwide (2008). (Adapted from Perfumer & Flavorist, 2009. A preliminary report on the world production of some selected essential oils and countries, Vol. 34, January 2009.)
producer of essential oils. China and India play a major role followed by Indonesia, Sri Lanka, and Vietnam. Many unique and unusual essential oils originate from the huge Australian continent and from neighboring New Zealand and New Caledonia. Major essential oil-producing countries in Africa include Morocco, Tunisia, Egypt, and Algeria with the Ivory Coast, South Africa, Ghana, Kenya, Tanzania, Uganda, and Ethiopia playing a minor role. The important spice-producing islands of Madagascar, the Comoros, Mayotte, and Réunion are situated along the eastern coast of the African continent. The American continent is also one of the biggest essential oil producers. The United States, Canada, and Mexico possess a wealth of natural aromatic plant material. In South America, essential oils are produced in Brazil, Argentina, Paraguay, Uruguay, Guatemala, and the island of Haiti. Apart from the above-mentioned major essential oil-producing countries there are many more, somewhat less important ones, such as Germany, Taiwan, Japan, Jamaica, and the Philippines. Figure 4.1 shows production countries and essential oil production worldwide (2008).
Cultivation of aromatic plants shifted during the last two centuries. From 1850 to 1950, the centers of commercial cultivation of essential oil plants have been the Provence in France, Italy, Spain, and Portugal. With the increase of labor costs, this shifted to the Mediterranean regions of North Africa. As manual harvesting proved too expensive for European conditions, and following improvements in the design of harvesting machinery, only those crops that lend themselves to mechanical harvesting continued to be grown in Europe. By the early 1990s, even North Africa proved too expensive and the centers of cultivation moved to China and India. At the present time, manual-handling methods are tending to become too costly even in China and, thus India remains as today's center for the cultivation of fragrant plant crops.
Not all odorous extracts of essential oil-bearing plants comply with the International Standards Organization (ISO) definition of an "Essential Oil." An essential oil as defined by the ISO in document ISO 9235.2—aromatic natural raw materials—vocabulary is as follows.
"Product obtained from vegetable raw material—either by distillation with water or steam or—from the epicarp of Citrus fruits by a mechanical process, or—by dry distillation" (ISO/DIS 9235.2,
1997, p. 2). Steam distillation can be carried out with or without added water in a still. By contrast, dry distillation of plant material is carried out without the addition of any water or steam to the still (ISO 9235, 1997). Note 2 in Section 3.1.1 of ISO/DIS 9235.2 is of importance. It states that "Essential oils may undergo physical treatments (e.g., re-distillation, aeration) which do not involve significant changes in their composition" (ISO/DIS 9235.2, 1997, p. 2).
An alternative definition of essential oils, established by Professor Dr. Gerhard Buchbauer of the Institute of Pharmaceutical Chemistry, University of Vienna, includes the following suggestion: "Essential oils are more or less volatile substances with more or less odorous impact, produced either by steam distillation or dry distillation or by means of a mechanical treatment from one single species" (25th International Symposium on Essential Oils, 1994). This appears to suggest that mixing several different plant species within the production process is not allowed. As an example, the addition of lavandin plants to lavender plants will yield a natural essential oil but not a natural lavender essential oil. Likewise, wild-growing varieties of Thymus will not result in a thyme oil as different chemotypes will totally change the composition of the oil. It follows that blending of different chemotypes of the same botanical species is inadmissible as it will change the chemical composition and properties of the final product. However, in view of the global acceptance of some specific essential oils there will be exceptions. For example, Oil of Geranium ISO/DIS 4730, is obtained from Pelargonium x ssp., for example, from hybrids of uncertain parentage rather than from a single botanical species (ISO/DIS 4731, 2005). It is a well established and important article of commerce and may, thus, be considered to be an acceptable exception. In reality it is impossible to define "one single species" as many essential oils being found on the market come from different plant species. Even in ISO drafts it is confirmed that various plants are allowed. There are several examples like rosewood oils, distilled from Aniba rosaedora and Aniba parviflora, two different plant species. The same happens with the oil of gum turpentine from China, where mainly Pinus massoniana will be used, beside other Pinus species. Eucalyptus provides another example: Oils produced in Portugal have been produced from hybrids such as Eucalyptus globulus subsp. globu-lus x Eucalyptus globulus subsp. bicostata and Eucalyptus globulus subsp. globulus x Eucalyptus globulus subsp. Eucalyptus globulus subsp. pseudoglobulus. These subspecies were observed from various botanists as separate species. The Chinese eucalyptus oils coming from the Sichuan province are derived from Cinnamomum longipaniculatum. Oil of Melaleuca (terpinen-4-ol type) is produced from Melaleuca alternifolia and in smaller amounts also from Melaleuca linariifolia and Melaleuca dissitiflora. For the future, this definition must be discussed on the level of ISO rules.
Products obtained by other extraction methods, such as solvent extracts, including supercritical carbon dioxide extracts, concretes or pomades, and absolutes as well as resinoids, and oleoresins are not essential oils as they do not comply with the earlier mentioned definition. Likewise, products obtained by enzymic treatment of plant material do not meet the requirements of the definition of an essential oil. There exists, though, at least one exception that ought to be mentioned. The well-known "essential oil" of wine yeast, an important flavor and fragrance ingredient, is derived from a microorganism and not from a plant.
In many instances, the commercial terms used to describe perfumery products as essential oils are either wrong or misleading. So-called "artificial essential oils," "nature-identical essential oils," "reconstructed essential oils," and in some cases even "essential oils complying with the constants of pharmacopoeias" are merely synthetic mixtures of perfumery ingredients and have nothing to do with pure and natural essential oils.
Opinions differ as to the historical origins of essential oil production. According to some, China has been the cradle of hydrodistillation while others point to the Indus Culture (Levey, 1959; Zahn, 1979). On the other hand, some reports also credit the Arabs as being the inventors of distillation. Some literature reports suggest that the earliest practical apparatus for water distillation has been dated from the Indus Culture of some 5000 years ago. However, no written documents have been found to substantiate these claims (Levey, 1955; Zahn, 1979). The earliest documented records of a method and apparatus of what appears to be a kind of distillation procedure were published by Levy from the High Culture of Mesopotamia (Levey, 1959b). He described a kind of cooking pot from Tepe Gaure in northeastern Mesopotamia, which differed from the design of cooking pots of that period. It was made of brown clay, 53 cm in diameter and 48 cm high. Its special feature was a channel between the raised edges. The total volume of the pot was 37 L and that of the channel was 2.1 L. As the pot was only half-filled when in use the process appears to represent a true distillation. While the Arabs appear to be, apart from the existence of the pot discovered in Mesopotamia, the inventors of hydrodistillation, we ought to go back 3000 years B.c.
The archaeological museum of Texila in Pakistan has on exhibit a kind of distillation apparatus made of burnt clay. At first sight, it really has the appearance of a typical distillation apparatus but it is more likely that at that time it was used for the purification of water (Rovesti, 1977). Apart from that the assembly resembles an eighteenth century distillation plant (Figure 4.2). It was again Levy who demonstrated the importance of the distillation culture. Fire was known to be of greatest importance. Initial heating, the intensity of the heat, and its maintenance at a constant level right down to the cooling process were known to be important parameters. The creative ability to produce natural odors points to the fact that the art of distillation was a serious science in ancient Mesopotamia. While the art of distillation had been undergoing improvements right up to the eighth century, it was never mentioned in connection with essential oils, merely with its usefulness for alchemical or medicinal purposes ("Liber servitorius" of Albukasis). In brief, concentration and purification of alcohol appeared to be its main reason for being in existence, its "raison d'être" (Koll and Kowalczyk, 1957).
The Mesopotamian art of distillation had been revived in ancient Egypt as well as being expanded by the expression of citrus oils. The ancient Egyptians improved these processes largely because of their uses in embalming. They also extracted, in addition to myrrh and storax, the exudates of certain East African coastal species of Boswellia, none of which are of course essential oils. The thirteenth century Arabian writer Ad-Dimaschki also provided a description of the distillation process, adding descriptions of the production of distilled rose water as well as of the earliest improved cooling systems. It should be understood that the products of these practices were not essential oils in the present accepted sense but merely fragrant distilled water extracts exhibiting the odor of the plant used.
The next important step in the transfer of the practice of distillation to the Occident, from ancient Egypt to the northern hemisphere, was triggered by the crusades of the Middle Ages from the twelfth century onward. Hieronymus Brunschwyk listed in his treatise "The true art to distil" about
25 essential oils produced at that time. Once again one should treat the expression "essential oils" with caution; it would be more accurate to refer to them as "fragrant alcohols" or "aromatic waters." Improvements in the design of equipment led to an enrichment in the diversity of essential oils derived from starting materials such as cinnamon, sandalwood, and also sage and rosemary (Gildemeister and Hoffmann, 1931).
The first evidence capable to discriminate between volatile oils and odorous fatty oils was provided in the sixteenth century. The availability of printed books facilitated "scientists" seeking guidance on the distillation of essential oils. While knowledge of the science of essential oils did not increase during the seventeenth century, the eighteenth century brought about only small progress in the design of equipment and in refinements of the techniques used. The beginning of the nineteenth century brought about progresses in chemistry, including wet analysis, and restarted again, chiefly in France, in an increased development of hydrodistillation methods. Notwithstanding the "industrial" production of lavender already in progress since the mid-eighteenth century, the real breakthrough occurred at the beginning of the following century. While until then the distillation plant was walled in, now the first moveable apparatus appeared. The "Alambique Vial Gattefossé" was easy to transport and placed near the fields. It resulted in improved product quality and reduced the length of transport. These stills were fired with wood or dried plant material. The first swiveling still pots had also been developed which facilitated the emptying of the still residues. These early stills had a capacity of about 50-100 kg of plant material. Later on their capacity increased to 1000-1200 kg. At the same time, cooling methods were also improved. These improvements spread all over the northern hemisphere to Bulgaria, Turkey, Italy, Spain, Portugal, and even to northern Africa. The final chapter in the history of distillation of plant material came about with the invention of the "alembic à bain-marie," technically speaking a double-walled distillation plant. Steam was not only passed through the biomass, but was also used to heat the wall of the still. This new method improved the speed of the distillation as well as the quality of the top notes of the essential oils thus produced.
The history of the expression of essential oils from the epicarp of citrus fruits is not nearly as interesting as that of hydrodistillation. This can be attributed to the fact that these expressed fragrance concentrates were more readily available in antiquity as expression could be effected by implements made of wood or stone. The chief requirement for this method was manpower and that was available in unlimited amount. The growth of the industry led to the invention of new, and to the improvement of existing machinery, but this topic will be dealt with later on.
Before dealing with the basic principles of essential oil production it is important to be aware of the fact that the essential oil we have in our bottles or drums is not necessarily identical with what is present in the plant. It is wishful thinking, apart for some rare exceptions, to consider an "essential oil" to be the "soul" of the plant and thus an exact replica of what is present in the plant. Only expressed oils that have not come into contact with the fruit juice and that have been protected from aerial oxidation may meet the conditions of a true plant essential oil. The chemical composition of distilled essential oils is not the same as that of the contents of the oil cells present in the plant or with the odor of the plants growing in their natural environment. Headspace technology, a unique method allowing the capture of the volatile constituents of oil cells and thus providing additional information about the plant, has made it possible to detect the volatile components of the plant's "aura." One of the best examples is rose oil. A nonprofessional individual examining pure and natural rose oil on a plotter, even in dilution, will not recognize its plant source. The alteration caused by hydrodistillation is remarkable as plant material in contact with steam undergoes many chemical changes. Hot steam contains more energy than, for example, the surface of the still. Human skin that has come into contact with hot steam suffers tremendous injuries while short contact with a metal surface at 100°C results merely in a short burning sensation. Hot steam will decompose many aldehydes and esters may be formed from acids generated during the vaporization of certain essential oil components. Some water soluble molecules may be lost by solution in the still water, thus altering the fragrance profile of the oil.
Why do so many plants produce essential oils? Certainly neither to regale our nose with pleasant fragrances of rose or lavender, nor to heighten the taste (as taste is mostly related to odor) of ginger, basil, pepper, thyme, or oregano in our food! Nor to cure diseases of the human body or influence human behavior! Most essential oils contain compounds possessing antimicrobial properties, active against viruses, bacteria, and fungi. Often, different parts of the same plant, such as leaves, roots, flowers, and so on may contain volatile oils of different chemical composition. Even the height of a plant may play a role. For example, the volatile oil obtained from the gum of the trunk of Pinus pinaster at a height of 2 m will contain mainly pinenes and significant car-3-ene, while oil obtained from the gum collected at a height of 4 m will contain very little or no car-3-ene. The reason for this may be protection from deer that browse the bark during the winter months. Some essential oils may act not only as insect repellents but even prevent their reproduction. In many cases, it has been shown that plants attract insects that in turn assist in pollinating the plant. It has also been shown that some plants communicate through the agency of their essential oils. Sometimes essential oils are considered to be simply metabolic waste products! This may be so in the case of eucalypts as the oil cells present in the mature leaves of Eucalyptus species are completely isolated and embedded deeply within the leaf structure. In some cases essential oils act as germination inhibitors thus reducing competition by other plants (Porter, 2001).
Essential oil yields vary widely and are difficult to predict. The highest oil yields are usually associated with balsams and similar resinous plant exudations, such as gurjun, copaiba, elemi, and Peru balsam, where they can reach 30-70%. Clove buds and nutmeg can yield between 15% and 17% of essential oil while other examples worthy of mention are cardamom (about 8%), patchouli (3.5%) and fennel, star anise, caraway seed, and cumin seed (1-9%). Much lower oil yields are obtained with juniper berries, where 75 kg of berries are required to produce 1 kg of oil, sage (about 0.15%), and other leaf oils such as geranium (also about 0.15%). 700 kg of rose petals will yield 1 kg of oil and 1000 kg of bitter orange flowers are required for the production of also just 1 kg of oil. The yields of expressed fruit peel oils, such as bergamot, orange, and lemon vary from 0.2% to about 0.5%.
A number of important agronomic factors have to be considered before embarking on the production of essential oils, such as climate, soil type, influence of drought and water stress and stresses caused by insects and microorganisms, propagation (seed or clones), and cultivation practices. Other important factors include precise knowledge on which part of the biomass is to be used, location of the oil cells within the plant, timing of harvest, method of harvesting, storage, and preparation of the biomass prior to essential oil extraction.
The most important variables include temperature, number of hours of sunshine, and frequency and magnitude of precipitations. Temperature has a profound effect on the yield and quality of the essential oils, as the following example of lavender will show. The last years in the Provence, too cold at the beginning of growth, were followed by very hot weather and a lack of water. As a result yields decreased by one-third. The relationship between temperature and humidity is an additional important parameter. Humidity coupled with elevated temperatures produces conditions favorable to the proliferation of insect parasites and, most importantly, microorganisms. This sometimes causes plants to increase the production of essential oil for their own protection. Letchamo have studied the relationship between temperature and concentration of daylight on the yield of essential oil and found that the quality of the oil was not influenced (Letchamo et al., 1994). Herbs and spices usually require greater amounts of sunlight. The duration of sunshine in the main areas of herb and spice cultivation, such as the regions bordering the Mediterranean Sea, usually exceeds 8 h/day. In India, Indonesia and many parts of China this is well in excess of this figure and two or even three crops per year can be achieved. Protection against cooling and heavy winds may be required. Windbreaks provided by rows of trees or bushes and even stone walls are particularly common in southern Europe. In China the Litsea cubeba tree is used for the same purpose. In colder countries, the winter snow cover will protect perennials from frost damage. Short periods of frost with temperatures below -10°C will not be too detrimental to plant survival. However, long exposure to heavy frost at very low subzero temperatures will result in permanent damage to the plant ensuing from a lack of water supply.
Every friend of a good wine is aware of the influence of the soil on the grapes and finally on the quality of the wine. The same applies to essential oil-bearing plants. Some crops, such as lavender, thyme, oregano, and clary sage require meager but lime-rich soils. The Jura Chalk of the Haute Provence is destined to produce a good growth of lavender and is the very reason for the good quality and interesting top note of its oils by comparison with lavender oils of Bulgarian origin growing on different soil types (Meunier, 1985). Soil pH affects significantly oil yield and oil quality. Figueiredo et al. found that the pH value "strongly influences the solubility of certain elements in the soil. Iron, zinc, copper and manganese are less soluble in alkaline than in acidic soils because they precipitate as hydroxides at high pH values" (Figueiredo et al., 2005). It is essential that farmers determine the limits of the elemental profile of the soil. Furthermore, the spacing of plantings should ensure adequate supply with essential trace elements and nutrients. Selection of the optimum site coupled with a suitable climate plays an important role as they will provide a guarantee for optimum crop and essential oil quality.
It is well known to every gardener that lack of water, as well as too much water, can influence the growth of plants and even kill them. The tolerance of the biomass to soil moisture should be determined in order to identify the most appropriate site for the growing of the desired plant. Since fungal growth is caused by excess water, most plants require well-drained soils to prevent their roots from rotting and the plant from being damaged, thus adversely affecting essential oil production. Lack of water, for example, dryness, exerts a similar deleterious influence. Flowers are smaller than normal and yields drop. Extreme drought can kill the whole plant as its foliage dries closing down its entire metabolism.
Plants are living organisms capable of interacting with neighbor plants and warning them of any incipient danger from insect attack. These warning signals are the result of rapid changes occurring in their essential oil composition, which are then transferred to their neighbors who in turn transmit this information on to their neighbors forcing them to change their oil composition as well. In this way, the insect will come into contact with a chemically modified plant material, which may not suit its feeding habits thus obliging it to leave and look elsewhere. Microorganisms can also significantly change the essential oil composition as shown in the case of elderflower fragrance. Headspace gas chromatography coupled with mass spectroscopy (GC/MS) has shown that linalool, the main constituent of elderflowers, was transformed by a fungus present in the leaves, into linalool oxide. The larvae of Cecidomye (Thomasissiana lavandula) damage the lavender plant with a concomitant reduction of oil quality. Mycoplasmose and the fungus Armillaria mellex can affect the whole plantation and totally spoil the quality of the oil.
As already mentioned, the cells containing essential oils can be situated in various parts of the plant. Two different types of essential oil cells are known, superficial cells, for example, glandular hairs located on the surface of the plant, common in many herbs such as oregano, mint, lavender, and so on, and cells embedded in plant tissue, occurring as isolated cells containing the secretions (as in citrus fruit and eucalyptus leaves), or as layers of cells surrounding intercellular space (canals or secretory cavities), for example, resin canals of pine. Professor Dr. Johannes Novak (Institute of Applied Botany, Veterinary University, Vienna) has shown impressive pictures and pointed out that the chemical composition of essential oils contained in neighboring cells (oil glands) could be variable but that the typical composition of a particular essential oil was largely due to the averaging of the enormous number of individual cells present in the plant (Novak, 2005). It has been noted in a publication entitled "Physiological Aspects of Essential Oil Production" that individual oil glands do not always secrete the same type of compound and that the process of secretion can be different (Kamatou et al., 2006). Different approaches to distillation are dictated by the location of the oil glands. Preparation of the biomass to be distilled, temperature, and steam pressure affect the quality of the oil produced.
Essential oils can occur in many different parts of the plant. They can be present in flowers (rose, lavender, magnolia, bitter orange, and blue chamomile) and leaves (cinnamon, patchouli, petitgrain, clove, perilla, and laurel); sometimes the whole aerial part of the plant is distilled (Melissa officinalis, basil, thyme, rosemary, marjoram, verbena, and peppermint). The so-called fruit oils are often extracted from seed, which forms part of the fruit, such as caraway, coriander, cardamom, pepper, dill, and pimento. Citrus oils are extracted from the epicarp of species of Citrus, such as lemon, lime, bergamot, grapefruit, bitter orange as well as sweet orange, mandarine, clementine, and tangerine. Fruit or perhaps more correctly berry oils are obtained from juniper and Schinus species. The well-known bark oils are obtained from birch, cascarilla, cassia, cinnamon, and massoia. Oil of mace is obtained from the aril, a fleshy cover of the seed of nutmeg (Myristica fragrans). Flower buds are used for the production of clove oil. Wood and bark exudations yield an important group of essential oils such as galbanum, incense, myrrh, mastix, and storax, to name but a few. The needles of conifers (leaves) are a source of an important group of essential oils derived from species of Abies, Pinus, and so on. Wood oils are derived mostly from species of Santalum (sandalwood), cedar, amyris, cade, rosewood, agarwood, and guaiac. Finally, roots and rhizomes are the source of oils of orris, valerian, calamus, and angelica.
What happens when the plant is cut? Does it immediately start to die as happens in animals and humans? The water content of a plant ranges from 50% to over 80%. The cutting of a plant interrupts its supply of water and minerals. Its life-sustaining processes slow down and finally stop altogether. The production of enzymes stops, auto-oxidative processes start, including an increase in bacterial activity leading to rotting and molding. Color and organoleptic properties, such as fragrance, will also change usually to their detriment. As a consequence of this, unless controlled drying or preparation is acceptable options, treatment of the biomass has to be prompt.
The timing of the harvest of the herbal crop is one of the most important factors affecting the quality of the essential oil. It is a well-documented fact that the chemical composition changes throughout the life of the plant. Occasionally, it can be a matter of days during which the quality of the essential oil reaches its optimum. Knowledge of the precise time of the onset of flowering often has a great influence on the composition of the oil. The chemical changes occurring during the entire life cycle of Vietnamese Artemisia vulgaris have shown that 1,8-cineole and b -pinene contents before flowering were below 10% and 1.2%, respectively, whereas at the end of flowering they reached values above 24% and 10.4% (Nguyen Thi Phuong Thao et al., 2004). These are very large variations indeed occurring during the plant's short life span. In the case of the lavender life cycle, the ester value of the oil is the quality-determining factor. It varies within a wide range and influences the value of the oil. As a rule of thumb, it is held that its maximum value is reached at a time when about two-third of the lavender flowers have opened and thus, that harvesting should commence. In the past, growers knew exactly when to harvest the biomass. These days the use of a combination of microdistillation and gas chromatography (GC) techniques enables rapid testing of the quality of the oil and thus the determination of the optimum time for harvesting to start. Oil yields may in some cases be influenced by the time of harvesting. One of the best examples is rose oil. The petals should be collected in the morning between 6 a.m. and 9 a.m. With rising day temperatures the oil yield will diminish. In the case of oil glands embedded within the leaf structure, such as in the case of eucalypts and pines, oil yield and oil quality are largely unaffected by the time of harvesting.
The first step is, in most cases, selection of plant seed which suits best the requirements of the product looked for. Preparation of seedbeds, growing from seed, growing and transplanting of seedlings, and so on should follow well-established agricultural practices. The spacing of rows has to be considered (Dey, 2007). For example, dill prefers wider row spacing than anise, coriander, or caraway (Novak, 2005). The time required before a crop can be obtained depends on the species used and can be very variable. Citronella and lemongrass may take 7-9 months from the time of planting before the first crop can be harvested while lavender and lavandin require up to three years. The most economical way to extract an essential oil is to transport the harvested biomass directly to the distillery. For some plants, this is the only practical option. Melissa officinalis ("lemon balm") is very prone to drying out and thus to loss of oil yield. Some harvested plant material may require special treatment of the biomass before oil extraction, for example, grinding or chipping, breaking or cutting up into smaller fragments, and sometimes just drying. In some cases, fermentation of the biomass should precede oil extraction. Water contained within the plant material has been classified by Yanive and Palevitch as chemically, physicochemically, and mechanically bound water (Yanive and Palevitch, 1982). According to these authors only the mechanically bound water, which is located on the surface and the capillaries of plants, can be reduced. Drying can be achieved simply by spreading the biomass on the ground where wind movement effects the drying process. Drying can also be carried out by the use of appropriate drying equipment. Drying, too, can affect the quality of the essential oil. Until the middle of the 1980s cut lavender and lavandin have been dried in the field, (Figure 4.3) a process requiring about three days. The resulting oils exhibited the typical fine, floral odor; however, oil yields were inferior to yields obtained with fresh material. Compared with the present day procedure with container harvesting and immediate processing (the so-called "vert-broyé") this quality of the oil is greener, harsher, and requires some time to harmonize. However, yields are better, and one step in the production process has been eliminated. Clary sage is a good example demonstrating the difference between oils distilled from fresh plant material on the one hand and dried plant material on the other. The chemical differences are clearly shown in Table 4.2. Apart from herbal biomass, fruits and seed may also have to be dried before distillation. These include pepper, coriander, cloves, and pimento berries, as well as certain roots such as vetiver, calamus, lovage, and orris. Clary sage is harvested at the beginning of summer but distilled only at the end of the harvesting season.
Seeds and fruits of the families Apiaceae, Piperaceae, and Myristicaceae usually require grinding up prior to steam distillation. In many cases, the seed has to be dried before comminution takes place. Celery, coriander, dill, ambrette, fennel, and anise belong to the Apiaceae. All varieties of pepper belong to the Piperaceae while nutmeg belongs to the Myristicaceae. The finer the material
is ground, the better will be the oil yield and, owing to shorter distillation times, also the quality of the oil. In order to reduce losses of volatiles by evaporation during the comminution of the seed or fruit, the grinding can also be carried out under water, preferably in a closed apparatus. Heartwood samples, such as those of Santalum album, Santalum spicatum, and Santalum austrocaledonicum
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