I have tried to look this up but have only come up with a few community sites with improper sourcing and varying degrees of answer (from 1 month to many years).
Does anyone have first hand knowledge or a reliable source?
The back of the bottle is written in Breton, which google translate doesn't support, but since it is close to French I think this is the line I am looking for:
Conservation du chouchen une fois ouvert des annees.
Which to me sounds something along the lines of 'once opened keeps for years', but it's just a guess.
I also know this is the Breton equivalent to mead, but I believe it's made with apple juice which I assume will make it go off faster.
Update: I opened this bottle when I posted this question, forgot about it in the cupboard and remembered it again over the weekend. It tasted absolutely fine (or at least the same as it did when I opened it). I will add an answer when/if the taste changes.