planning on brewing 12 lbs of 2 row I milled 3 weeks ago. It’s been kept in a vacuumed Ziplock garment bag and in a cool dark space. Should be fine right?
A bunch of folks will tell you that the grain will oxidize and you should mill it just before use. A bunch of other folks will tell you it’s not a problem. After gathering information and evaluating your outcomes, you’ll have to choose which camp you fall into.
One other distinction that should be is that there is no debate about whether or not the milled malt oxidizes, rather the issue at hand is whether or not that oxidation is noticeable. Heck, just about everything oxidizes on this planet…
Another accelerator of oxidation is heat generated during milling. For this reason the mill should always be run as slowly as possible. Don’t know the rate of this effect, but I’ve recently compared (I bake also) conventionally milled (roller) whole wheat flour and some milled on slow turning stone burrs, and in comparison you would never want to eat anything made from the former. Bitter, sour, flavorless, rancid from oxidation of lipids. Malt will probably suffer much less, but there’s something to this. Heat always accelerates oxidation. (At the extreme, it’s called “fire!”)
The thing you want to avoid which is LOX is stored in the arcospire of the malt, its tucked within the kernel pretty well. The moment that is crushed, it is allowed to touch oxygen and oxidation starts. It takes a little as 15 minutes for that process to happen.