Dairy agriculture surfaced in Europe several millennia ago, and as the technology progressed, farmers found that different types of dairy cows were better suited for different climates and requirements. The primary types of cows were classified into Holstein/Friesian, Brown Swiss, Jersey, and Zebu. Throughout Europe's dairy history, fresh milk has always been enjoyed by those who lived in rural areas and were able to feed their cows with fresh pasturage. But in the cities, where dairy cows tended to be poorly fed, there were incidents of fatalities in children due to toxic pathogens in the milk. Quality milk, therefore, as a commercial good, was a relative luxury for most of its history, at least in urban areas.
When French scientist Louis Pasteur developed pasteurization, a method of treating milk with heat to kill off potentially harmful pathogens, at the end of the 19th century, however, dairy went through a kind of revolution as safe milk became readily available to rapidly urbanizing populations in Europe and America.
Today, the two most common cows found in dairy production are the Holstein/Friesian and the Jersey cow. Jersey cows are notable for having the highest fat and sugar contents in their milk, thus making them a particularly good milk for complementing the sweetness of espresso.
The sugar found in milk is called lactose, which is composed of two simple sugars: glucose and galactose. Coincidentally, both of these sugars make up a large part of the carbohydrates found in roasted coffee. Lactose accounts for half the calories found in a glass of milk and makes an enormous contribution to the flavor. The animals' feed also greatly affects their milk's sugars. If a cow is fed a diet of dry grass, the milk it produces tends to have a more savory and salty taste. On the other hand, if a cow is free-range and fed fresh pasturage, its milk leaves a sweet, rich finish on the palate.
Fat must also to be taken into account in understanding milk as it relates to espresso. As consumers and baristas, we often look for a whole-fat milk (3.2 percent to 3.5 percent milk fat) when we want to pair our coffee with something rich and satisfying. Milk's fat lives in globules surrounded by a membrane composed of lipids and proteins. The membranes of each individual globule prevent the globules from meshing together to make one giant blob of fat. Further, they protect the globules from enzymes that would consume them and leave the milk with little or no sweetness.
The membranes are very important when it comes to introducing high heat to milk. In the process of heating, the proteins in the milk increase in mass, thus making the milk thicker. This is why a wholefat milk works better for steaming: more fat globules means more protein-enriched membranes, which, in turn, produces a more sturdy foam.
Two basic proteins are found in milk, known to most of us simply as the dietary staple of Little Miss Muffet: curds and whey. Curd proteins, called caseins, form the thickness of milk, while the whey proteins contribute to the liquid. The whey protein, however, also contributes to the texture of caseins when it comes to foam. Casein proteins are more common in milk than whey proteins, but both are important in providing a balance to the milk.
The elements and building blocks of milk, although they may be a dry area of study, are important for a barista to know. Consider, for example, how we seek to understand the chemical composition of coffee. The questions about how coffee is grown, processed and roasted are all ones we seek answers to in trying to develop a better understanding of that honey-like substance oozing from the portafilters in our cafés. Some baristas even go as far as to travel to the country from which their coffees originate. This is not an easy thing for most baristas to do, with the expense of traveling and taking time off from work. It's not like coffee grows in our backyard. But when it comes to milk, it is relatively easy for any one of us to seek out a local dairy farm and go visit.
So that's what I did.