318
Chapter 18 · Enchanting Chemistry - Natural Flavors and Fragrances
18
(78 °C) and can therefore be gently removed in
vacuum. However, other solvents such as petroleum ether, hexane, toluene or methanol are also
used. Supercritical carbon dioxide is even more
suitable for extraction: At temperatures above
31 °C and pressures above 74 bar, CO 2 is in the
“supercritical state”. In this state, it simultaneously possesses the properties of gases and liquids: The fluid has the high density of liquids
and the low viscosity of gases. These properties
can be controlled by varying pressure and temperature. At high densities, the solubility of the
essential oils is increased. A well-known process
of extraction with supercritical carbon dioxide is
the decaffeination of coffee (7 Sect. 16.3).
When organic solvents are used for extraction, not only the components of the essential
oils are dissolved, but also by-products such as
waxes and dyes. Therefore, the concrète obtained
after the removal of the solvents is usually a solid,
colored mass. This is undesirable for further use
in perfumes. Therefore, the concrète is dissolved
in ethanol, the solid components are separated
and the ethanol is removed again. The resulting alcohol-free but completely ethanol-soluble
product for fragrance applications is called
essence absolue.
A special extraction method known since
ancient times, enfleurage, is a particularly gentle process for the absorption of plant substances
by fats as extracting agents (French: enfleurage,
“scented with flowers”). For this purpose, freshly
harvested flowers are sprinkled on glass plates,
which have previously been coated with an odorless fat, e.g. lard from cattle or pigs (. Fig. 18.7).
The essential oils are absorbed by the fat by diffusion at ambient temperature. After a few days,
the old flowers are replaced by new ones and this
process is repeated for several weeks or months.
At the end of this enfleurage, a fat saturated with
the scent of flowers is obtained, which is called
“pomade”. The essential oils can be washed out
of this pomade with ethanol, and the fat separated from the ethanol solution. The pure flower
oil is then called essence absolue d’ enfleurage.
Since this process is very time-consuming and
labor-intensive, it is only used for particularly
high-quality flowers such as jasmine, and the
products are consequently expensive.
The process can be accelerated by raising
the temperature (enfleurage à chaud, or maceration after Italian macerare for soaking). Fat and
Today, about 150 commercial essential oils exist,
which compete with about 3000 different synthetic fragrances and flavors. More than 10,000
fragrances and flavors have already been identified in nature. About 75% of all substances used
in the fragrance and flavor industry are produced
by synthetic processes; only about 25% are isolated from natural sources. In the following, the
most important processes used to produce essential oils from natural raw materials are explained,
because only these can be regarded as “renewable
raw materials” in the context of this book.
18.3 Extraction of Essential Oils
The extraction of essential oils from vegetable
raw materials for the production of fragrances
and flavors can be achieved in three different
ways. The choice of the process depends on different preconditions:
5 type of material to be treated (flowers, fruits,
leaves, seeds, bark, etc.)
5 stability and reactivity of the fragrances and
flavors contained in the product
5 product specifications (consistency, ingredients, etc.)
The three most important processes, pressing,
extraction and steam distillation, are described
in more detail below, and typical areas of application are outlined.
Pressing is carried out exclusively for the
extraction of oils from citrus fruits. For this purpose, the oil-containing outer skin of the fruit
is pressed at room temperature (so-called cold
pressing process). This method is very mild and
gentle and is therefore particularly suitable for
citrus oils, which are very sensitive to heat and
tend to change their aroma at elevated temperatures. An exception to this is lime oil, whose
aroma change during distillation is desired in
some cases. By pressing out the peel at room
temperature, essential oils from oranges, lemons,
bergamots, mandarins, grapefruits and limes are
obtained.
The second method, extraction, is well
known from household use, where, e.g., tea
leaves are extracted with boiling water to produce tea. Plants are extracted analogously with
cold or warm organic solvents. A preferred solvent is ethanol, which has a low boiling point
Chapter 18 · Enchanting Chemistry - Natural Flavors and Fragrances
18
(78 °C) and can therefore be gently removed in
vacuum. However, other solvents such as petroleum ether, hexane, toluene or methanol are also
used. Supercritical carbon dioxide is even more
suitable for extraction: At temperatures above
31 °C and pressures above 74 bar, CO 2 is in the
“supercritical state”. In this state, it simultaneously possesses the properties of gases and liquids: The fluid has the high density of liquids
and the low viscosity of gases. These properties
can be controlled by varying pressure and temperature. At high densities, the solubility of the
essential oils is increased. A well-known process
of extraction with supercritical carbon dioxide is
the decaffeination of coffee (7 Sect. 16.3).
When organic solvents are used for extraction, not only the components of the essential
oils are dissolved, but also by-products such as
waxes and dyes. Therefore, the concrète obtained
after the removal of the solvents is usually a solid,
colored mass. This is undesirable for further use
in perfumes. Therefore, the concrète is dissolved
in ethanol, the solid components are separated
and the ethanol is removed again. The resulting alcohol-free but completely ethanol-soluble
product for fragrance applications is called
essence absolue.
A special extraction method known since
ancient times, enfleurage, is a particularly gentle process for the absorption of plant substances
by fats as extracting agents (French: enfleurage,
“scented with flowers”). For this purpose, freshly
harvested flowers are sprinkled on glass plates,
which have previously been coated with an odorless fat, e.g. lard from cattle or pigs (. Fig. 18.7).
The essential oils are absorbed by the fat by diffusion at ambient temperature. After a few days,
the old flowers are replaced by new ones and this
process is repeated for several weeks or months.
At the end of this enfleurage, a fat saturated with
the scent of flowers is obtained, which is called
“pomade”. The essential oils can be washed out
of this pomade with ethanol, and the fat separated from the ethanol solution. The pure flower
oil is then called essence absolue d’ enfleurage.
Since this process is very time-consuming and
labor-intensive, it is only used for particularly
high-quality flowers such as jasmine, and the
products are consequently expensive.
The process can be accelerated by raising
the temperature (enfleurage à chaud, or maceration after Italian macerare for soaking). Fat and
Today, about 150 commercial essential oils exist,
which compete with about 3000 different synthetic fragrances and flavors. More than 10,000
fragrances and flavors have already been identified in nature. About 75% of all substances used
in the fragrance and flavor industry are produced
by synthetic processes; only about 25% are isolated from natural sources. In the following, the
most important processes used to produce essential oils from natural raw materials are explained,
because only these can be regarded as “renewable
raw materials” in the context of this book.
18.3 Extraction of Essential Oils
The extraction of essential oils from vegetable
raw materials for the production of fragrances
and flavors can be achieved in three different
ways. The choice of the process depends on different preconditions:
5 type of material to be treated (flowers, fruits,
leaves, seeds, bark, etc.)
5 stability and reactivity of the fragrances and
flavors contained in the product
5 product specifications (consistency, ingredients, etc.)
The three most important processes, pressing,
extraction and steam distillation, are described
in more detail below, and typical areas of application are outlined.
Pressing is carried out exclusively for the
extraction of oils from citrus fruits. For this purpose, the oil-containing outer skin of the fruit
is pressed at room temperature (so-called cold
pressing process). This method is very mild and
gentle and is therefore particularly suitable for
citrus oils, which are very sensitive to heat and
tend to change their aroma at elevated temperatures. An exception to this is lime oil, whose
aroma change during distillation is desired in
some cases. By pressing out the peel at room
temperature, essential oils from oranges, lemons,
bergamots, mandarins, grapefruits and limes are
obtained.
The second method, extraction, is well
known from household use, where, e.g., tea
leaves are extracted with boiling water to produce tea. Plants are extracted analogously with
cold or warm organic solvents. A preferred solvent is ethanol, which has a low boiling point