There are recommended food rotation guides on this website that tell you approximately how long different items will last. My mother gifted me with old flour in the food storage #10 cans. I don’t like wasting food, so I opened it and tried some. The cans are 15 years old and the flour tasted like it the nutrients had been sucked out, plus it had a very strong aftertaste of metal. This might be what many websites refer to as leaching. I’m still doing research to rule that out.
From the research I did, white flour will last longer than wheat flour because the fats have been mostly removed. Fats go rancid fast. This is why white flour will last longer in storage than wheat flour. The metallic taste in my old flour #10 cans is most likely just the flour going bad, not necessarily metal leaching from the can.
Some possible suggestions to remove the funky tin taste is to leave the flour out in a bowl, stir it, give it a few hours, and eventually the weird taste goes away. Another idea is to put a raw potato, cut in half, into the flour and leave it over night in a cool place, like the fridge, or cool basement, then throw the potato away and the tin flavor will go away. I will try that with some flour and share how it goes.