Professor Abbott’s Five Foam Factors teach us that the conditions for producing superior latte foam are very specific.
The two main protein types in milk are caseins and whey proteins.
Casein acts as an emulsifier for homogenised fats.
Whey protein is the principal surfactant in milk.
Surfactants make milk foams more elastic by reducing the surface tension between the air and the bubble film known as the lamella.
Milk fat is mostly found in the form of a globule. The large globules in raw and unhomogenised milk have a lower density than much of the material in milk and will rise to the surface. This phenomenon is known as creaming. The casein in homogenised milk interacts with the broken-up milk fat globules and prevents them from coalescing, keeping the milk in a more even emulsion.
Lactose is a disaccharide, made up of galactose and glucose bonded together. Lactose is 70% less sweet than sucrose.
Rheology in foam science is the measure of a foam’s firmness. For latte art purposes, we need foams to be firm to create a silky texture, but we also need a low yield stress to allow bubbles to slide past each other for ease of pouring.
Lipolysis is a process wherein triglycerides are damaged and break apart into free fatty acids. The process of lipolysis causes the free fatty acids, which are surface active, to displace the stabilizing surfactant whey proteins from the bubble films, causing foams to rapidly break up.
Ostwald ripening: Gases in air bubbles having relatively higher air pressure diffuse into neighbouring bubbles having relatively lower air pressure,