How long can you keep a wine kit before you make the wine?
I don’t know, but as it is a food product, it should have a “best by” date printed on the packaging somewhere.
I found an old wine kit - at least one year old, maybe two - and decided to try it. The result was not pleasant! It tasted oxidized, stale, old, and generally not worth drinking. I assumed the concentrate was bad, but it could have been the yeast or just a random infection or temperature control problem.
I didn’t bottle it; maybe it would have been excellent had I given it some time. I donated it to my septic tank and assumed the yeast would help keep the tank working.