Short answers, pulled from the story.
Adult digestion of milk relies on lactase persistence. Thousands of years ago a chance mutation spread in human populations in northwestern Europe that enabled lactase production in adulthood. Lactose intolerant individuals lack enough of the enzyme lactase and have trouble digesting the lactose in milk.
French chemist and biologist Louis Pasteur invented pasteurization in 1863. He developed it while on summer vacation in Arbois to remedy the acidity of local wines, heating young wine to about 50 to 60 degrees Celsius briefly to kill microbes. The process was named in his honor.
Humans first consumed the milk of other mammals after domesticating animals during the Neolithic Revolution. Lipid residue in prehistoric pottery shows dairying was practiced in Southwest Asia by at least the seventh millennium BC.
Milk is an emulsion of butterfat globules in a water-based fluid containing dissolved carbohydrates, proteins, and minerals. Full fat milk contains about 33 grams of fat per liter, and normal bovine milk contains 30 to 35 grams of protein per liter, about 80% of it arranged in casein micelles. The sugar lactose gives milk its sweet taste.
Ultra-heat treatment heats homogenized milk to 138 degrees Celsius for 2 to 4 seconds, destroying all bacteria and letting the milk keep for up to six months unopened without refrigeration. Standard high temperature short time pasteurization heats milk to 72 degrees Celsius for 15 seconds, keeping it safe for up to three weeks if continually refrigerated.
Fat globules and casein micelles in milk are large enough to deflect light, producing its opaque white color. Fat-free skimmed milk has only casein micelles, which scatter shorter-wavelength blue light more than red, giving it a bluish tint. Carotene can lend a golden hue in some breeds such as Guernsey and Jersey cattle.