Why does cooking oatmeal starting with cold milk make it creamy?

I'd always made oatmeal according to the "traditional" method of bringing the liquid to boil first, then adding the oatmeal. I recently discovered a recipe that calls for adding the oatmeal to cold liquid first, then bringing the mixture to boil - the claim is that that technique results in creamier oatmeal.

Upon trying this recipe, I found that, indeed, the resulting oatmeal was creamier than the traditional method. Can anyone explain the food science behind why cooking oatmeal starting from a cold liquid yields a creamier end result than by dropping the oatmeal into already-boiling/simmering liquid?

Best Answer

Flour and cornmeal are well known to clump when added cold to boiling water. Such clumps arise when starch molecules unball and forming a mesh that traps other starch molecules, preventing them from hydrolysing in the same way. Hence lumpy gravy and sauces.

For oatmeal I've observed similar clumping behaviour, but not to the same extent. Anyway I suspect the same mechanism is at work. Since starch hydrolysis is the main reaction making oatmeal creamy, I'm not surprised that slow and steady heating is considered best.