Citronella Oil Extraction Methods
The leaves of the citronella grass are usually harvested in the early morning and then dried on the ground outside of the distrilleries. Drying requires only 3 to 4 hours in bright sunlight but, much longer during the rainy season. While drying, the leaves must be turned over periodically to prevent fermentation. Careful short drying of the leaves is beneficial to the quality of the oil, whereas long drying, especially in the rain, is harmful. The leaves should not be exposed for any length of time to sun or rain, and the material should be distilled the same day that it is harvested. If this cannot be done, it should be dried inside the factory or under sheds or on platforms near the boiler.
The distillers prefer to distill dried leaves, because they can charge more into a still and because the distillation of dry leaves requires less steam and fuel. During periods of continued rain the crop has to be distilled in a wet condition and, for this reason, most distillers today stop operating in rainy weather. The sereh grass should be weed free during the drying process, however, when oil prices are low few distillers can afford this precaution. Many distillers do not bother to cut the leaves into short pieces prior to distillation. Whole leaves occupy more space in the retort than chopped material, and because of uneven distribution in the still, steam channeling and a lower yield of oil will result. Chopping of the leaves increases the economy of a still.
The faster the steam passes through the charge, the lower the oil percentage per kilogram of condensed steam. If the steam passes too slowly through the charge, the time of distillation will be longer and the hourly yield of oil per kettle lower. Most distillers today use distilled and exhausted leaves as fuel, low priced wood being available only in a few localities.
Distillation starts rapidly and slows up gradually after about two-thirds of the oil has been distilled. The average yield of oil is about .7%; it fluctuates from .5% in the rainy season to 1.2% in the dry season. A still charged with 1,500 kg. of dried, chopped leaves of good quality yields about 12.5 kg. of oil.
If an oil with a high content of geraniol and citronellal cannot be obtained in a certain place, with plants raised from good stock, other factors such as soil, climate, season, and age of the plants come into play.
From the the above statments it would appear that the native distillers, who raise their own sereh grass, should be able to produce a better grade of oil than those large-scale distillers who have to buy their leaf material from numerous native growers. The distillers cannot be very selective, because the competition for grass is keen, and the native planters usually play one distiller against another. It should be mentioned, however, that not all small native grower-distillers produce a very high quality of oil because their sereh grass is often contaminated with weeds, or is cut too young or too old. In order to obtain the maximum yield of oil, the small distillers often dry the leaves in the sun prior to distillation, and extend the time of distillation until the charge is completely exhausted, which gives an inferior quality of oil with a low citronellal content.
Source:http://www.wsu.edu/~gmhyde/433_web_pages/433Oil-web-pages/essence/essence-oils.html
