For someone who has a background in materials physics, working with exotic materials has been a fun and exciting experience. I have worked with plastics that conduct electricity, can emit light (in LEDs), and even transform solar energy to useful electrical energy. Virtually no technology would exist today, if not for advances in materials science and engineering.

In the broad spectrum of fascinating materials, biomaterials and materials that our body makes, like blood and milk, have a special place. These are extremely complex materials that only our (or animals) bodies can make. For instance, we still drink milk from cows, goats, and buffaloes, we donate blood to save lives, and we extract stem cells from bone marrows. The sheer complexity of some materials does not allow us to easily re-engineer them. Milk is one such amazing material.

Composition of milk

Milk is a rich material from a composition perspective, containing fat, proteins, lactose, water and minerals. Complexity of milk as a material arises from the manner in which many of the components exist in it. For instance, fat exists as globules in an oil/water emulsion. The size of these globules is about 1–10 microns and can be seen under an optical microscope. Cow’s milk typically has 3–6% of fat. Some breeds like the holstein (the one with black and white patches) produce lower fat (3–4%), whereas other breeds like the jersey (smaller brown ones) produce higher fat (5%). The amount of fat also varies with the type of animal. Buffaloes, for instance, produce milk with about 8% fat. There are several types of proteins in milk including casein (majority) and whey proteins. Casein exists in a colloidal form with micelles in the 10–100 nm range, which can be seen under an electron microscope. Since the size of protein micelles and fat globules is comparable to the wavelengths of visible light, they act as scatterers. Scattering by fat globules in relative wavelength independent, so we see that thick, white, opaque feature of milk. Scattering by protein micelles is governed by the Tyndall effect, where blue light is scattered more than red. This explains why skim milk (0% fat, only protein) has a slight bluish tinge (also our iris looks blue due to the same reason!). In addition to fat and protein, milk contains lactose (sugar) that is found completely dissolved as a true solution. As you can see, this is a complex mix of many organic molecules organized across various sizes. And this is a simplified picture of what milk contains. There are minerals, vitamins A, D,K, riboflavin and who bunch of other molecules in milk! Isn’t that amazing!