3,432. Designating Tithes in a Barrel of Wine

Hilchos Maaser 7:1

Let’s say that someone has 100 log of wine that are considered untithed under Biblical law. If he says that the two log that he will take are terumah, ten are first tithe and nine are second tithe, he may not start drinking and leave the terumah and tithes for the end. Rather, he must separate the portions, after which he may drink. We don’t say that the wine that remains at the end is considered to have been put aside retroactive to before he started drinking. This is because the obligation of terumah and tithes is Biblical; when it comes to Biblical law, we don’t consider the gifts to have been separated until they have actually been separated.

Hilchos Maaser 7:2

If someone specifies that his tithes are at the top of the barrel, he may not drink from the bottom. If he specifies that they’re at the bottom, he may not drink from the top. This is because liquids mix. However, if one specified that tithes of produce were at the top of a vessel, he may eat from the bottom; if at the bottom, he may eat from the top.