How to Make Great Coffee Consistently, According to Science
"The best thing for people to do is to locate each variable systematically."
Roughly 83 percent of American adults drink coffee regularly, adding up to an impressive 587 million cups of java consumed per day. How many of those coffees are actually good is another question altogether. Consistently excellent espresso can be rare, even if a brewer is regularly making it.
That is, unless you’re thinking like a scientist. Christopher Hendon, Ph.D., assistant professor of computational materials and chemistry at the University of Oregon, is part of a team of scientists doing just that. On Thursday, at the 255th National Meeting and Exposition of the American Chemical Society in New Orleans, Hendon and his team are presenting what they claim is the best method for making reproducible, delicious espresso coffee. Chemistry plays a major role in creating a great cup of joe, but physics and mathematics are especially important. Hendon would know — his nickname in the academic world is “Dr. Coffee.”
“The most important thing someone can do to vastly improve their brewing is to use a scale to weigh the mass of coffee and water used in brewing,” Hendon tells Inverse. “There is a complex relationship between grind size, mass, brew time, and overall cup quality. The best thing for people to do is to locate each variable systematically.”
The most important variables that affect the reproducibility of coffee, he says, are the water, the freshness of the beans, the process of grinding, and the way all those components are mixed together.
Because water “hardness” varies throughout the U.S., the flavor profiles of the resulting coffee will vary, too, even if the same beans are used every time. Hard water, which has high levels of magnesium and calcium, results in brews with a stronger flavor than soft water because caffeine compounds stick to the magnesium during the brewing process.
“Something that really matters is how much bicarbonate is dissolved in the water — how hard the water is,” says Hendon. “Actually, hardness is not technically correct, because that is a measurement of both the calcium and bicarbonate concentrations, but the point is that high buffering water will mute the acids in the coffee. We like the acidic flavors, so we usually want water with lower bicarbonate concentrations.”
The best beans to use are those that are freshly roasted. That’s because they contain carbon dioxide and other volatile compounds that, over time, escape the beans, resulting in less flavorful coffee.
The scientists say you should keep your coffee in the fridge to keep it fresher for longer because doing so slows the rate of evaporation. When it’s time to grind, the trick is getting the coffee beans just small enough. Smaller particles mean better-tasting coffee, but when they’re too small, they can stick together and decrease extraction.
Finally, when you actually extract espresso from beans, Hendon and his team say that the water needs to come into contact with the grounds uniformly. Ideally, all the grounds make contact with water equally, which is not what happens with a traditional drip-brew coffee pot in which water just drips into the center of the grounds.
Using a French press, says Hendon, is “an excellent method” for achieving uniformity for extraction, but there are better ways.
“We actually refer to brew methods as either full-immersion or percolation-based,” says Hendon. “Full immersion means that the coffee and water are in contact with each other the entire time, whereas percolation methods [pour over, espresso, etc.] rely on some force to push the water through the bed of coffee. Obviously, water will find the path of least resistance, which means inhomogenous extractions.”
The Best Cup?
Hendon argues that if every single American cafe implemented these careful procedures, then the U.S. would save $300 million a year by reducing the amount of coffee beans used to make espresso.
So what’s the best cup Dr. Coffee has ever had? It was created by none other than the 2016 U.S. Brewers Cup champ.
“The most impressive cup I ever had was brewed backstage before my friend Todd Goldsworthy was about to compete in the Brewers Cup,” says Hendon. “This coffee he made me was so extremely floral and clean tasting; it was nothing like I had ever experienced.”
“The coffee itself was from Panama and the water was ideal — using a recipe similar to my ‘ideal’ recipe, 2:1 metals to bicarbonate. He made a pour over.”
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