Probably indefinitely since it is basically a liquid sugar with a preservative. However add it several months before bottling because it may begin fermentation again as it did with my wine. I bottled it 1-1/2 months after adding and still have detectable carbonation in my wine. I decant it several hours before drinking it and it is good.

I have some I bought last year and it appears to be good. I'm going to use it. I just stored it in the wine making part of my shop. Nothing special. Temps run between Winter 40 and summer 80. Don't worry a different part of the same shop is used for fermentation and storage. There the temp is 62 to 64 all the time.

I have only stored these pouches for a few months at a time. I keep them iin an area with temps about 68° . All good.

You can store it for a long time I have used stuff that was 5 years old. Most sweeteners are very shelf stable. Kind of like honey and candy syrup. As long as you keep oxygen out it shouldn’t spoil.