The Science of Sustainability

Coffee Flavor By the Numbers

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droplet of coffee

It’s practically impossible to brew the same cup of coffee each day. New technology to analyze and automate coffee brewing helps anyone bring reproducibility to his or her morning coffee routine.

The perfect cup of coffee can be quantified in terms of its strength, also called total dissolved solids, and the percent of flavors extracted from the beans during brewing. Let’s get technical about the numbers.

Back in the 1960s, Ernest E. Lockhart, a researcher at the Massachusetts Institute of Technology, made pots of coffee with varying strengths and degrees of extraction. Then he asked people which brew they preferred. From that survey, and another follow-up by the Specialty Coffee Association of America, numerical standards emerged to describe the perfect cup of coffee: a brew with 1.15-1.35% dissolved solids and 18-22% of the possible flavors extracted.

You can measure these numbers for your coffee at home. A handheld device called a refractometer shines light through a droplet of coffee, measuring how much the light waves bend as they travel through the liquid. The amount of dissolved solids in the coffee – including sugars, acids, and flavors from the coffee as well as the minerals in the water — affect how much the light bends, and thus the reading on the device.

coffee refractometer

Enter that percentage of dissolved solids from the refractometer, as well as the weight of water and beans you used, into an iPhone app called MoJoToGo to calculate the extraction percent.

In an article for Gizmodo, Matt Buchanan describes his quest to brew a cup of coffee with the extraction percentage sweet spot of 19%:

"I tear through a $16.50 one-pound bag of coffee in about three days, making coffee over and over again, seeking the mythical number 19. I use a version of the French Press technique from Everything But Espresso. Start the kettle. Weigh the beans. Grind the beans. Wait for the water to reach 206 degrees. Pour 400g of the heated water onto the grounds. Start the timer. Pat the coffee bloom. Dunk the coffee bloom. Wait 4-5 minutes. Plunge. Pour. Check result in MoJoToGo. Curse.

The most frustrating part isn't the resulting Ahab-like hunt for the ever-elusive 19 percent. It's the revelation of how imprecise my methods are. The 18.3 percent cup that sends me into a delirious orbit before I even taste it is quickly followed by one that measures 16 percent (and tastes like it). I'm all over the map. It drives me insane. And to Amazon, to buy more precise equipment."

Brewing the perfect cup of coffee by hand is messy, imprecise and frustrating. And again technology comes to the rescue. The Trifecta MB, a new machine made by Bunn, brings reproducibility to coffee brewing, one cup at a time.

It’s the home version of a commercial machine with 10 programmable functions, including water temperature, brew time and the amount of stirring with air bubbles, to precisely control brew conditions to highlight the best flavors in the beans. Watch the commercial version in action:

Portola Coffee Lab in Costa Mesa, CA has several Trifectas in the shop. Owner Jeff Duggan writes on the shop blog that he typically spends hours developing a unique brewing program for a new coffee.

"This machine has become the clearest example of our brewing standards," he writes. “It uses technology to put us more in touch with coffee rather than neuter it and make it into a new version of a vending machine.”

Armed with Portola’s program, a bag of their beans and your own Trifecta, you could brew coffee at home that tastes just like what they brew in the shop. Some roasters post their optimized programs on Trifecta's website so anyone can brew a tasty batch of their coffee.

Technology advances the artistry of coffee, for what really matters is taste. Gadgets, apps and machines help coffee connoisseurs find conditions that brew the best coffee according to their tastebuds, whatever that extraction percentage or brew time may be.

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Category: Chemistry, Engineering, Food

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Melissae Fellet

About the Author ()

Melissae Fellet is a freelance science writer obsessed with electrons, atoms and molecules. Writing about chemistry, physics and technology, she hopes to reveal how the invisible building blocks of matter influence things like plastics, perfumed shampoos and the speedy computer chips we use everyday. She holds a BS in biochemistry and microbiology from the University of Florida and a PhD in chemistry from Washington University in St. Louis. She spends sunny days at her home in Santa Cruz either watching otters in the bay or tromping around the redwood forests.
  • swagv

    Unfortunately, I've had 19% extraction coffee and sometimes found it inferior to 18.6% or 19.5% extraction cups. There isn't one magic number, unfortunately.

  • http://twitter.com/GabrielRoybal Gabriel Roybal

    artistry and routine seem like polar opposites to me.

  • http://twitter.com/GabrielRoybal Gabriel Roybal

    how much does a machine like that cost?