OK, this might seem blindingly obvious, but I am a bit curious.
First some back story:
Being the poor college student that I am, I eat a lot of soup. I try to avoid raman and such and go for the slightly more expensive, but more nutritious, canned soups. So today I was making pea soup from a can (andersons brand, I highly recommend it) and noticed that though it comes out of the can as a thick unappetizing paste, as it heats up it becomes delicious soup. No added liquids needed. How do they do that? I am assuming that the water is trapped in fat or gelatin or something, but want to know what the real deal is.
Just a simple question, probably created by hunger.
Pea soup, in particular, is more solid at room temp (and even more so refrigerated) than when heated, even if it’s homemade. Much of it has to do with saturated fats which are solid at lower temperatures but melt when heated.
The real question is why does homemade pea soup stay thicker after reheating. (Thicker than it was hot the day it was made, I mean, not thicker than when cold.) I always need to add more water to the leftovers.
In both cases, I suspect starches. Starch is listed prominently on the ingredients list of many soups - probably because it thickens it and makes it seem more hearty. It would make sense for it to become thicker on cooling - it may become more thoroughly mixed in as the liquid warms up. I’m just WAGging, so we’re clear.
I am going to WAG that the answer is gelatin, or some close analog of it. At lower temperatures, the gelatin congeals. As it is heated, it becomes fully liquid again. Voila.
WhyNot, your pea soup is thicker on reheating because some of the liquid in it evaporated on the first heating, and even more on the second heating. If you reheat it enough times, you will create some type of pea-based concrete.
One time I didn’t finish my extra-large bowl of pho (I know; shame!) and I took it home. The next day it had the consistency of Jell-O in my refrigerator. Went back to normal when I microwaved it. Not sure what caused that; likely beef fat in the soup. (Mmmm)
It’s just a matter of the attraction of the molecules to one another in a cool state. Heating, shaking or other agitation breaks the bonds and liquefies it.