I have a wooden bread bin, with the bottom (floor) bit being a 3.6mm plywood. The rest of the build is solid wood, 12mm thickness. The bin was dropped at one point and the bottom of it cracked; the moisture got in and mould started growing on it.

I decided to replace the bottom altogether and got the same thickness plywood - to make sure it fits into the slots on the sides, front and back. However the question is how to finish it - to make sure it's both water proof and food safe, after all, bread would be resting on it most of the time.

I did consider options such as linseed oil or even olive oil, but those may not be durable enough and (at least in olive oil case) have some odour, which wouldn't be great in a small enclosed bread bin. Ideally, I'd like a film-like finish for protection, but a normal wood stain isn't food safe.

So, what's the best finish for the bottom of the bread bin?

P.S. I'm in the UK if it matters.