I have a small bag of what looks like crushed rock salt (we know it isn't salt) that came with wine-making supplies. Can anyone tell me what it is?
I got the kit from an individual, not a company. It had a pack of pectic enzyme, a hydrometer, an air lock, and the unlabeled bag mentioned. It's not silica gel.
I did not buy it from a store, and it is not in the original packaging.

My first guess would be a cleaner or sanitizer.

Is there a list of what was included with the kit? Maybe you can go through the list and mark off everything that you know to see what is left on the list and what it could be.

edit: Worst case scenario, ask the person you bought the kit from...