A common question in the shop is how long grains will last after milling, and our standard answer is to use them within about a month or two, and keep them sealed well against moisture. One of the reasons this comes up is that sometimes a recipe will call for 5 or 6 ounces of a specialty malt, but you can only find it in full pounds where you shop, meaning you head home with a partial bag of milled specialty grains which may or may not get used up in the next month or two.
I wanted to point out a small but meaningful difference in how we package and mill your grains. For starters, most if not all specialty grains we stock are sold in 4 ounce, 8 ounce, and 16 ounce sizes and we did this to help tailor what you need to purchase to better match your recipe. If you needed 5 ounces, for example, we would weigh 5 ounces out of an 8 ounce bag and ONLY mill the 5 ounces you need. The rest is resealed for you (as it will last for many months in this condition, perhaps years) and when you need it milled for another recipe, bring it back in and we'll mill it for free.
Like I said, this is a small thing, but I know many people have only had the option of purchasing in 1 pound (16 ounce) sizes and ending up with some portion milled and going stale. You bought more than you needed and now that extra stands a chance of going to waste.
I hope that helps answer one of those common questions we are often asked!