Adventures in Milk! Cheese is biohacking (Part 1)
“Milk is food for the beginning eater, a gulpable essence distilled by the mother from her own more variable and challenging diet.”
— Harold McGee, On Food and Cooking
Milk is a fascinating food. It’s the first food we all eat and it’s a critical part of our own humanness. Our identity as mammals is bound in our lactation, a mammal literally is a “creature of the breast”. McGee continues: “When our ancestors took up dairying, they adopted the cow, the ewe, and the goat as surrogate mothers. These creatures accomplish the miracle of turning meadow and straw into buckets of human nourishment. And their milk turned out to be an elemental fluid rich in possibility, just a step or two away from luxurious cream, fragrant golden butter, and a multitude of flavorful foods concocted by friendly microbes.”
Milk is an amazing food. Along with fruit, it’s one of the only foods that are actually evolutionarily designed to be eaten. It’s a key part of our human history and credited, in part, with humankinds exit from the fertile crescent and proliferation around the globe. Milk is a clever food because it exploits our biology to achieve its goal — to transfer nutrients and calories from forage to fawn. You can tell a lot about an animal by the composition of its milk.
Compare, for example, to difference in composition between bison and polar bear milk (and spare a thought for the poor soul who had to milk a polar bear …for science) and how they describe the leanness of each animal. Human milk is among the highest in lactose (milk’s unique sugar) perhaps to fill the needs of a growing brain which runs mainly on sugars rather than proteins or fat. Whale milk is exceptionally high in fat too, maybe a key to keeping whale calves warm in the frigid oceans.
To be successful, milk has to possess certain qualities. 1) a mother mammal needs to be able to synthesize it from components in her diet. 2) It must be microbiologically clean to prevent transferring illness to the newborn and 3) it needs to contain the right balance of nutrients to take the cub, calf, fawn, from infancy to adolescence (or in the case of humans, toddlerhood). On top of all this, 4) it needs to be sufficiently thin in viscosity to flow through the mother’s nipple — a challenging feat if you’re also trying to make something nutrient dense.
For the rest of this discussion I’m going to focus on cow’s milk though the ideas apply to all animal milks, perhaps excluding cockroaches. Holstein cow milk is about 3.5% fat, 3.1% protein, and 4.9% lactose. While it’s still mostly water (~87% by weight) cow’s milk actually supersaturated with both protein and calcium. That’s to say that if you tried to dissolve milk’s proteins or it’s calcium in a glass of water individually and to the same proportions, you couldn’t. Solid particles would settle out. This would be a painful problem if you were trying to say, push that chunky fluid out of your nipples. Fortunately for mothers everywhere, milk has an answer! While its protein and calcium contents, when taken alone could cause trouble for the fluid, casein proteins in milk form astounding and still puzzling structures with calcium that allow both to solubilize. The proteins and calcium form a co-dependent system that keeps milk viscosity thin and smooth.
At the heart of milk is the protein casein. Casein makes up 80% of the proteins in milk and the specific ways it folds and interacts with other proteins enables many of the transformations we know as modern dairy from yogurt to cheese. Even the whiteness of milk is due to casein proteins scattering light. Casein proteins form large clusters called “micelles” as seen above. As we’ll see next week, these micelles are critical to delivering nutrients to a baby calf through two specific mechanisms. It’s precisely these mechanism that we’ll hack in cheesemaking, more to come next week…