If you don’t happen to know or live near where your milk comes from, as most people don’t, you can tell by the color and the separation. Having had a cow, for my own personal use, green fed cow milk is yellow and separated. (good for butter but not fun to drink- I prefer my goat milk for drinking-if they are on their vitamins it’s good). Likewise goat milk is yellowish compared to standard store milk which is white, white, white. 80% of dairies not only don’t feed pasture, they don’t even feed green hay, they feed silage, which has had the beta carotene fermented out of it. Weston Price showed pasture fed milk , especially mineral rich pasture fed milk as being yellower, even bright yellow.