2,425. What Foods Combine

Maachalos Assuros 14:5

It has already been explained that the items prohibited by the Torah don’t combine to form the minimum volume of an olive necessary for liability except for a neveila with a treifa, and the prohibitions of a nazir. The five species of grain, their flour and their dough all combine to form the volume of an olive vis-à-vis the prohibitions of chometz on Pesach, eating new grain before the omer has been brought, second tithe and trumah.

Maachalos Assuros 14:6

The Rambam opines that everything from which trumah and tithes must be separated combines to form the volume of an olive vis-à-vis untithed produce because it’s all one prohibition. This is like the carcasses of an ox, a sheep and a deer which all combine to form the volume of an olive as has already been addressed.