I use 2 - 3 oz. in some recipes. I've been keeping it in a zip loc bag in my freezer. Any idea how long it will still be effective in my mash?
I buy it in 55 lb sacks and store it in a bin with an airtight seal. No problem well into the second year.
If it's crushed it will not last as long, but it seems to keep about as well as other grain, and your taking good care of it.
vacuum seal or a tight saran wrap would be better than zip lock to protect from oxidation if crushed.
Are you just using some for a mash pH adjustment? If so it should last pretty much indefinitely. You'd be using such a small amount that any oxidation in the grain shouldn't be noticeable.