Milk appears "empty" under an optical microscope because the major protein (casein) is in the form of micelles, about 0.1 µm in diameter, i.e., below the resolution power of the optical microscope. Electron Microscopy, one of the major tools of nanoscience, can be used to determine the structure of these nanoscopic components of our most common food products.  Milk products such as yogurt and cheese originate through the coagulation of the casein micelles. Heating of milk at >85°C alters the casein micelle surface. b-Lactoglobulin (as one of the two major whey proteins) interacts with k-casein and the complex adheres to the micellar surface where it prevents the micelles from indiscriminate coagulation. Only short branched chains may be formed. The structure retains all the liquid phase of milk in yogurt.

 

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