Malt does go stale. There was a period of several years when I was unable to brew and I had crushed grains (crystal, brown and amber) which were in sealed and unopened polythene bags stored in picnic cooler boxes so at least they were perfectly dry. They were also perfectly hot as they spent two summers in a very dry put uninsulated loft. When I packed up my brewery in Poole, some of the stuff had already reached its BB date and when I was able to set up shop again in Brittany, I would say some of it had been crushed 7 or 8 years earlier. While it was still hard and crisp, the lack of freshness was discernible in the taste and smell and this carried over to the beer. The beer was far from undrinkable, but it could have been a lot better. I don't think guest drinkers noticed, but they wouldn't know what it was supposed to taste like, anyway. Neverthless, I've never had the slightest problem with two-year-old base malt mainly because I keep it in its sack, in a sealed, food-grade maceration drum and my garage doesn't get hotter than the mid twenties even at the hottest part of the day in mid summer- so the mass of malt probably never gets warmer than 20C. I've recently invested in a proper malt mill (I've collected a couple of those crappy, tinned, Chinese coffee grinders. I wouldn't recommend them) and have started buying uncrushed grains, which means I now longer have to justify a 30Kg order to get the best value for carriage fee and so I can let my stocks run down a bit. I should also add that, little by little, the very old stuff has been chucked and replaced.
The moral of the story is that I would have no hesitation in using properly stored, crushed base malts even 2 or 3 years old especially if I lived in Alderney. But it's not really the base malts that hang around for ages. How long does it take to get through a kilo of patent black malt, for example, if you're only using it to add colour?
