This has bugged me for awhile, since I occasionally put cream in my coffee. This is the standard pasteurized, homogenized stuff (e.g., Hood) that you can buy at the grocery store. It’s fine when you open it, but a few days later, the cream starts to form knots. It tastes and smells fine, but it’s a little unappetizing.
Why does this happen? I’ve even seen this happen with Mini-Moos (you know, those little shelf-stable, one-serving cream pods), which in addition to being ultra-pasteurized, are sealed until you use them. In both cases, vigorous shaking can sometimes break up these clumps, sometimes not.
Just recently I also was wondering about that. I figured dehydration by evaporation, and the effects were especially apparent because of the higher fat content inevitable in the solution (both numerically and spatially), as opposed to dehydration of relatively more consistently homogenous water foods.
Cream has a high fat content. Milk tends to lump after a while, too. In this case, they’re small lumps of butter. I figured that it’s because you can’t strain it all out. Fat tends to aggregate if you give it long enough. It’s not curdling, at least.