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==== Resin ====
As indicated earlier, most resins are complex mixtures of terpenes. In the case of balsams, a significant proportion of non-terpenoids (benzoic and cinnamic acids) is present. For many resins, the terpene mixture consists of a volatile fraction (primarily containing monoterpenoids and sesquiterpenoids, i.e. C10 C<sub>10</sub> and C15 C<sub>15</sub> compounds) and a non-volatile fraction (containing mainly di- or triterpenoids, i.e. C20 C<sub>20</sub> or C30 C<sub>30</sub> compounds). For hard resins such as copal and benzoin the amounts of volatile compounds present are negligible or small and no attempt is made to separate them in any post-harvest processing from the much larger quantities of non-volatile compounds. For soft resins or oleoresins such as pine resin and Manila elemi, the volatile fraction (essential oil) forms a significant proportion of the total mass (up to 30% or more) and may be separated by steam distillation from the non-volatile part of the resin. Crude pine resin is always distilled to yield its essential oil (turpentine).
It is not only the proportions of volatile and non-volatile fractions that vary greatly amongst the different resins; the composition of the respective fractions is also very variable, both qualitatively and quantitatively. Within a genus the compositional differences between species may also be considerable. This is particularly true in ''Pinus'', where the turpentine is much more variable than the non-volatile fraction. Even within a species, the composition of pine resin can vary markedly according to provenance; ''P. merkusii'' is a case in point: Indonesian and Thai populations have quite different turpentine compositions to Filipino ones and within the former provenances there are further significant differences. For all these reasons there is little point in trying to detail chemical compositions here, either actual, average or "typical"; where details are available they are given in Chapter 2.
