3,270. Terumah From Olives for Oil and Other Cases
Terumos 5:18
One may not take stalks of grain as terumah for kernels, nor olives for oil, nor grapes for wine. If one did so, what he separated isn’t terumah. This is a rabbinic enactment intended to prevent the kohein from being troubled to tread the grapes or press the olives. One may take oil as terumah for olives being pickled and wine as terumah for grapes being dried. This is comparable to taking terumah from two species that are not considered mixed species to one another, taking terumah from the superior type for the inferior. Similarly, one may take terumah from olives to be squeezed for olives to be pickled but not vice versa, from unboiled wine for boiled wine but not vice versa, and from clear wine for non-clear wine but not vice versa. One may take terumah from a certain number of fresh figs for a certain number of dried figs and from a certain volume of dried figs for a certain volume of fresh figs, but not from a volume of fresh figs for dried figs or from a number of dried figs for fresh figs. The reason for this is because one should always give terumah generously. [Fresh figs are generally more desirable, but there are more dried figs per volume.] One may take terumah from wheat kernels for bread, but not from bread for wheat kernels based on the calculation of kernels in the bread. In all these cases, if one did take terumah, what he separated is terumah.
Terumos 5:19
We don’t take terumah from oil for olives being pressed or from wine for grapes being tread because this resembles taking terumah from produce whose work has been completed for produce whose work has not been completed. If one did take such terumah, what he separated is terumah, but he must take terumah from the actual olives and grapes. The first creates meduma (a mixture of terumah and secular produce) by itself. [More on this in halacha 22.] One who eats it is liable just like one is liable for eating other whole terumah. Such is not the case with the second terumah taken.