Coffee is unique among artisanal beverages in that the brewer plays a significant role in its quality at the point of consumption. In contrast, drinkers buy draft beer and wine as finished products; their only consumer-controlled variable is the temperature at which you drink them.
Why is it that coffee produced by a barista at a cafe always tastes different than the same beans brewed at home?
It may be down to their years of training, but more likely it’s their ability to harness the principles of chemistry and physics. I am a materials chemist by day, and many of the physical considerations I apply to other solids apply here. The variables of temperature, water chemistry, particle size distribution, ratio of water to coffee, time, and, perhaps most importantly, the quality of the green coffee all play crucial roles in producing a tasty cup. It’s how we control these variables that allows for that cup to be reproducible.
How Strong a Cup of Joe?
Besides the psychological and environmental contributions to why a barista-prepared cup of coffee tastes so good in the cafe, we need to consider the brew method itself.
We humans seem to like drinks that contain coffee constituents (organic acids, Maillard products, esters, and heterocycles, to name a few) at 1.2 to 1.5 percent by mass (as in filter coffee), and also favor drinks containing 8 to 10 percent by mass (as in espresso). Concentrations outside of these ranges are challenging to execute. There are a limited number of technologies that achieve 8 to 10 percent concentrations, the espresso machine being the most familiar.
There are many ways, though, to achieve a drink containing 1.2 to 1.5 percent coffee. A pour-over, Turkish, Arabic, Aeropress, French press, siphon, or batch brew (that is, regular drip) apparatus—each produces coffee that tastes good around these concentrations. These brew methods also boast an advantage over their espresso counterpart: They are cheap. An espresso machine can produce a beverage of this concentration: the Americano, which is just an espresso shot diluted with water to the concentration of filter coffee.
All of these methods result in roughly the same amount of coffee in the cup. So why can they taste so different?
