Why does fine powder (like flour or powder milk) mixes evenly when stirred in cold water, but not in hot water (where the mixture becomes lumpy)?
In: Chemistry
Most powders dissolve better in hot water because the molecules of water have more energy and are “bumping” into the powder molecules. Hot water molecules have more energy and move more than cold molecules.
In some powders, mostly those that contain starches, the rapid mixing of the powder and hot water becomes a problem. The hot water immediately bonds with the outer layer of the bits of powder, but they form a shell which prevents water from reaching the subsequent layers of powder.
It’s because the heat “cooks” the molecular chains, causing them to bind. Same reason why you should always rinse a flour bowl with cold water. I’m gonna make some rolls now. Dammit.
Because hot water causes starches to expand like inflatable spring snakes. They end up getting tangled together and you end up with clumps. Cold water allows the mixture to evenly distribute themselves before expanding.
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