3,260. Terumah in Only Part of a Vessel

Terumos 4:19

The previous halacha applies to terumah gedolah; terumas maaser is different because it can be separated from produce in another location. When it comes to terumas maaser, as soon as the vessel ascends from the wine vat, the condition has been met and what he separated is terumas maaser, even if the vessel later breaks or spills back into the vat. It goes without saying that this is the case if what he separated is rendered ritually unclean.

Terumos 4:20

If someone declares the produce in the upper part of a vessel to be terumah and the produce in the lower part to be regular produce, or vice versa, his words are effective. This is because the designation of terumah depends on the intentions of the one separating it.