Suppose a gentile is a homebrewer who later converts to Judaism. Fermentation and aging can be long-running processes, so even if he knew to anticipate the problem and ceased homebrewing activities when he began the conversion process, he might have product remaining when he becomes a Jew. Per halacha, is he allowed to drink what he made? Sources please.
The equipment used for brewing is not used for anything else. Typically such equipment includes a plain metal pot (for boiling water and grain), a wort chiller (copper tubing placed in the pot through which cold water is run), glass carboys (for fermenting), glass bottles (eventually, for bottling the finished product), and various dedicated plastic or rubber items like siphon hoses and fermentation locks. Only the pot and the wort-chiller are in contact with hot liquid. The equipment, naturally, hadn't been toiveled.
Assume the homebrewer, like many, is fastidious about cleanliness, boiling and sterilizing everything that can be before each use.
The ingredients for beer are all pareve and (AFAIK -- correct me if I'm wrong) do not require a hechsher: malted barley, hops, yeast. Ingredients in mead are honey, yeast, and possibly spices or fruit (assume not grapes).
If it makes a difference because of terumah, ma'aser, shmita, etc., assume this person does not live in Eretz Yisrael.
The then-gentile was present for all stages of production.
I've limited this question to beer and mead because I know wine has special considerations.
On the one hand it seems like he can't drink it because he wasn't mindful of kashrut considerations at the time -- by happy coincidence he might not have done anything problematic, but he wasn't paying attention to that at the time. On the other hand, there might be leniencies bedieved, just as the rabbis instituted the sale of chametz rather than destroying it, for reasons of economics or waste.
I know a convert who was in this situation and was told no, but no reasoning was given and I think the equipment had been used for wine too, not just beer and mead. So I'm curious about what the answer, with reasoning, would be in the case that doesn't involve wine.