[novaRom]

But how do they store and preserve that surplus for a longer time cheaply? Probably dehydration helps, but it adds some energy and storing costs.

[themaninthedark]

It's not always stored, sometimes it is spoiled.

https://www.thecooldown.com/outdoors/mississippi-delta-farme...

At one point more was sent to developing countries as aid but that practice was curbed as it was undercutting local farmers.

[riffraff]

I think most national reserves are cereals (wheat, rice) which are naturally long lasting.

There's some storage of special products (dairy, pork, famously maple syrup) but those have ad-hoc storage.