Milk kefir whey is a liquid part of the over fermented kefir. Over fermentation considered to be the process when kefir grains left too long in the milk. Then whey separates from the curds.
It’s well known that whey is very rich with vitamins and minerals, proteins, primarily of α-lactalbumin and β-lactoglobulin, bovine serum albumin, and immunoglobin. It also contains and a very low level of fat.