I only buy it once, and use it again and again for years when I make sauerkraut or any kind of fermented food
Is it possible and beneficial?
Thomas, you don't want to keep probiotics for a long time - they are living bacteria and will die fairly quickly compared to most things. For instance, if you waited a year (just a guess based on years of experience, no formal source) the potency of the probiotic will be much less because many of the bacteria will have died. If you buy it, you should use it on a regular basis until it's gone - including using it in sauerkrat!
Hope this helps.