3,479. Demai Doesn't Apply to...

Hilchos Maaser 13:14

When the rule of demai was instituted, it was not applied to the following cases, all of which are exempt from demai: one who buys produce for planting or for use as animal feed; one who buys flour for tanning hides or for a medical dressing; one who buys oil to light as fuel or to apply to vessels: one who buys wine for use as eye drops; challah separated by an unlearned person; a mixture of terumah and secular produce; produce bought with second-tithe money; flour left over from a korban mincha offering; and produce added to the first fruits. If an unlearned person says that the requisite portions have been take, one need not tithe it.

Hilchos Maaser 13:15

Let’s say that someone buys produce to eat but he changes his mind and decides to use it as animal feed. In such a case, he shouldn’t sell it to a non-Jew or feed it to an animal – not even an animal belonging to someone else – until he has tithed it as one does demai.