How long will these foods last?

[Plinkplonk77]

Earlier in the year I bulk bought some lentils, oats, quinoa and couscous. A colleague says dried foods like this last forever if stored correctly, but a search online says a few years depending on which food. Has anyone tried eating these foods after several years/decades? Is the best way to store them in airtight containers, or in the freezer, or another way?

Several years yes. For pasta, popcorn, dried beans.

Brown rice does not do as well.

Keep the grains cool and dry. Plastic buckets, mylar (vacuum sealer bags) and oxygen absobers will increase the lifespan further.

Always sniff/taste anything you are not sure of.

We regularly eat 5 year old stuff (pasta/rice/beans/tins) as part of our rotation. Some tins go bad if stored in a warm place. Especially baked beans as they are slightly acidic.

The higher the oil content (brown rice, flour and soy beans) the faster they go rancid. Also, grains that have been processed or milled go off faster than whole ones.
Its a good idea to wrap them well and freeze them for 48+ hours to kill any dust mites and insect eggs.
Take them out of the freezer, defrost and bring to room temperature, then make sure they are absolutely dry before you vacuum seal them. Nylon bags only last a year so repack and seal them annually when the bags go soft. Mylar bags will last for decades, but not all types of vacuum sealers will seal them. You can use oxygen absorbers but you don't have to.

I would ask why you want to store them for five years. Why not use them as part of your normal meals and replace as you use? Then you will be eating oldest first while still having a good stock.

Thanks everyone. I was thinking of bulk buying more as a precaution for any disruption in food supplies or higher inflation over the next few years. I'm feeling a little unsure about where the next few years are heading and would like to have some basics there if needed. We are working through what I bought earlier in the year which is probably going to take a while, hence why I'm thinking if I buy now, it may be years before we actually eat it. Or am I being a bit mad to do this?

No you aren't mad, look at how much the cost of imported foods went up after Brexit.
We don't rotate our long term dried goods. Its packed in Mylar which is too expensive to keep replacing.
Shorter term batches are in nylon vacuum seal bags, the bags are cheap but only last about a year. To test them I take a few out and sprout them. As long as the majority sprout, the grains or beans are in good condition. The only thing that doesn't work for is red lentils. If fewer than half the grains sprouted we'd eat them, and since I know the dates I bought them that will tell me their shelf life.

I don't know about a few years, but I've been eating my way through a couple of bags of quinoa which DD bought and I inherited on her going to uni. They're about a year out of date and are absolutely fine.

Thank your everyone! Does anyone have any recommendations for particularly good but not too expensive freezer bags?

I buy the cheap pound shop ones and double up.

I like IKEA bags, I wash and reuse them, they do get thin and split but do a fair few rounds before they do.

I have some freezer bags but can't access them. They are being guarded by a spider.