This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The quantities obtainable from the various plants differ widely. It depends on the degree of ripeness, age, etc., of the materials. In general we may take for granted that all plants, whether the flowers, seeds, fruits or tissues, are the principal sources, yield more oil, when they have been allowed to completely ripen, than when they are used in imperfectly ripened state. We append under the respective headings of the essential oils, principally used for compounding by carbonators, the figures that show the usual practical results, and indicate also the special method for obtaining the oils.
The essential oils are divided into three large groups, namely: those which are free from oxygen, those containing oxygen, and those containing sulphur, besides the elements carbon and hydrogen. The latter group is very small, having but few representatives, the most important of which is oil of mustard. It is obtained from mustard seed by distillation. The seed does not naturally contain the oil, but produces it by a process of fermentation. The group of oxygen-free essential oils is continuing to diminish. Recent investigations, in which G. Haensel, a German manufacturing chemist, has taken an important part, show that almost all essential oils contain oxygen, and that the oxygen is the bearer of the aroma. The oxygenated oils consequently form the most numerous group, and include the most valuable products.