Oh my,I didn’t know powdered milk was so complicated. I too just keep it around in case of an emergency.
The powder milk will not dissolve. It needs to be worked to make it “instantized”. The powder milk just floats on top of water without dissolving, like throwing a cup of flour into water. The process runs it thru a boiler fired wetting process with steam. It’s then shaken, evaporated, and cooled which produces those granules of milk. Those dissolve instantly.