Several mishnayot: 1 - A long list of those items that are prohibited and in a mixture, prohibit the entire mixture in any amount. 2 - Libation wine that falls into a cistern prohibits the entire mixture, though it could be sold to an idolater, as long as the libation wine itself is not compensated. 3 - If a stone wine press is covered with pitch, by a non-Jew, and then covered in wine - that is usable. But if it were made of wood - that might be usable (with cleaning), or the alternate view - peel off the pitch altogether. If earthenware, there's no usability. Also, the Gemara delves into how to purify a wine press.