Lemongrass 407
either fresh or after wilting. Wilting herbage prior to distilling reduces moisture
content and increases oil recovery. Drying in the sun reduces oil recovery but
has little effect on oil composition. Generally, Clevenger apparatus is used for
distilling small quantities (up to 1.0 kg) of the herb in the laboratory. Large-field-
scale distillation units are fabricated to distil 500 kg or more of the herb at a time. On
an average, the herbage of C. flexuosus contains 0.2–0.4% oil and the oil yield is
100–125 kg/ha/year.
Oil of lemongrass is a viscous liquid, yellow to dark yellow or dark amber in
colour turning red on prolonged storage. The presence of water imparts a turbid
appearance. Whole oil is mainly used as a source of citral. Differentiation of lemongrass
oils into West Indian and East Indian in trade has no geographical significance as oils
from both species are produced in both areas. However, the West Indian oil has less
citral and more myrcene than the East Indian oil. Although both oils have a pronounced
fresh lemony fragrance, the odour of East Indian is stronger (Kamath et al, 2001).
East Indian is considered fresher, lighter and sweeter.
Morphological characters like plant height, number of tillers/plant and number of
leaves/plant is significantly correlated with essential oil yield/plant. Maximum elimicin
content as a major chemical constituent of oil had also been observed at flowering
stage. Among the physiological characteristics, a significant correlation was observed
between essential oil content and crop growth rate (r = 0.6018) as well as net assimilation
rate (r = 0.9474). The oil of lemongrass is chemically reactive. The terpene mixture
undergoes a series of complex reactions when exposed to air and sunlight. It is slowly
converted into a dark coloured viscous resinous substance on keeping. However, if
stored in aluminium or stainless steel vessels insulated from air, water and light, the
quality of the oil is stable for long periods of time.
Solvent extraction
Distillation being a high temperature process, yields an oil with a burnt note. Also it
is devoid of volatile fractions. An oil of softer note is yielded by solvent extraction.
However, the process is more expensive than steam distillation. Lemongrass oil can
be extracted by the following methods using different solvents.
1Maceration: this involves macerating the dried plant material in the presence of
a non-polar solvent like hexane, filtering and concentrating the extract to recover
the solvent.2 Percolation: in this method, the solvent is made to percolate through a column of
the dried plant material. The percolate is later subjected to distillation to obtain
the oil and recover the solvent. Soxhlet extraction is a method of continuous
percolation using special equipment. The plant material is packed in a porous
container placed inside an extraction vessel. The solvent is introduced slowly
and continuously into the container. The extract is siphoned into a recovery
vessel where the solvent is distilled off. The solvent thus recovered is added back
into the porous container. The process is repeated in a cyclic manner such that
extraction of the material and recovery of the solvent proceeds simultaneously
using a limited quantity of solvent.Spent grass
The residue obtained after extraction of the oil is called spent grass. It can be used as
cattle feed fresh or after ensilaging. It can be used for mulching or manuring crops as