The Science of Steep

Brewing coffee has been elevated to a higher level of expertise than ever, but the perfect cup isn't out of reach for the home barista
November 10, 2016Words by Joseph MeehanPhotos by Bryson Malone

With the rise of specialty coffee, it seems that coffee served in cafes has been elevated to a place where the home cup cannot follow, but in fact achieving the same level of quality as your favorite third-wave cafe is well within grasp of the amateur barista. 

When making a cup of specialty coffee, there are four crucial variables that the professional barista controls for: water to coffee ratio, particle size, steep time and temperature. When brewing at home, you yourself can control them in the same manner to bring out the best flavors in your coffee and get the most out of your prized beans. But long before you start your water boiling, long before the baristas dial in their multi-thousand dollar espresso machines, whether the beans are specialty single-origin or your favorite blend from the supermarket, the humble coffee bean begins its life as a seed. 

Organic Acids
Five organic acids make up the majority of coffee’s flavors.

  • Citric Acid: has a sour and fruity taste
  • Acetic Acid: Imparts a pleasantly clean and sharp sweetness
  • Quinic Acid: Has a bitter, astringent taste
  • Malic Acid: Tart taste with a lingering flavor
  • Chloragenic Acid: Bitter flavor on rear of tongue

Contrary to the name, coffee beans are not actual beans. They are seeds found in the fruit of the coffea genus of plants that grow throughout the tropical regions of the world. The fruit is grown and harvested on a farm and then sent to milling stations for processing. The end product of the milling process is green coffee, which is turned its familiar brown color during the roasting process.   

Modern roasters are more involved in the farming, harvesting and milling points of the supply chain. Crop inconsistencies from year to year used to force roasters to blend varieties of coffee together, tweaking bean ratios from year to year to keep flavor consistent. But modern third-wave roasters like Four Barrel Coffee, based in San Francisco, work with exporters and millers to find coffee of exacting quality, which they taste test in a lab to determine flavor viability. Once approved, exporters visit the farm where the coffea plants are cultivated to be sure workers’ conditions are adequate and the farm is well-maintained, two big factors in consistent coffee production. 

Specialty coffee is roasted lightly to emphasize the flavors and aromas that reside in the bean.

Roasting is where the final flavor profile of the bean will be determined. Often referred to as a City Roast, specialty coffee is roasted lightly to emphasize the properties of the thirty organic acids and hundreds of volatile compounds that reside in the bean. Where volatile compounds give coffee its aroma, organic acids provide the flavor. With some careful preparation and execution, roasters coax flavor compounds out of the beans at the optimum ratios to brew a perfect cup. 

When using manual equipment, the four most important variables are water-to-coffee ratio, temperature of the water, steep time, and particle size.

While the traditional drip coffee maker will do on mornings when you lurch out of bed barely early enough to make it to work on time, specialty coffee will always have a place in the hearts of those who want to go through a more involved process for an exponentially more expressive cup. To that end, manual brewing equipment such as a pourover cone or French press is essential. When using manual equipment, the four most important variables are water-to-coffee ratio, temperature of the water, steep time, and particle size. Keeping these variables consistent from brew to brew and tweaking them to your liking is the key to making the perfect cup at home. 

Manual brewing equipment, an essential for the perfect home cup.

Keeping water temperature consistent is the easiest place to start. A kettle with a built-in thermometer will give the most precise results. Short of that, bring your water to a boil, pull it from the heat, then wait 45 seconds and your water will be just right.

According to Brett, barista and educator at Four Barrel, one of the easiest ways to improve your home cup is to use a scale to measure precisely the ratio of water to coffee. “Weigh your water and weigh your coffee,” he said. “15 parts water to 1 part coffee is a good starting point. This will change the game for any home brewer.” The ratio of 15:1 can be used in any brewing method and for any size cup or carafe, and it will get you in the ballpark of the optimal ratio of volatile oils and organic acids. 

Pay close attention to the recommended steep times for your brewing equipment using the included instructions or the resources on your favorite roaster’s website. Use a kitchen timer or your watch to time each step of the brew process in order to avoid over- or underextraction.

If you’re hitting the right times for your equipment but not enjoying your cup, it’s time to tweak the particle size. 

Regional Flavors
Coffee acquires its distinctive flavors from the variety of processing traditions throughout the world.

  • Central America: Balanced acidity and sweetness
  • South America: Sweet, medium-bodied, with a distinctive acidity
  • Ethiopia: Wide variety due to a range of climates and processing methods
  • Kenya: Savory-sweet with a touch of acidity or tartness
  • Indonesia: Savory and herbaceous with a dark cocoa finish

The next step for the home brewer is a burr grinder. “A burr grinder allows you to control the particle size by increasing or decreasing the proximity of the burrs to one another,” said Brett, which will allow you to grind your coffee to the same relative particle size every time you brew in order to precisely control of one of the most important variables of the process. Equally importantly, you can adjust the particle size larger or smaller to tailor your extraction to your particular taste. Brett also suggests, in the case of not being ready to invest $100+ in an automatic burr grinder, to buy only enough coffee for the week and ask your barista to grind it for your preferred brew method. Fresh ground just before brewing is the best option, and you may get some funny looks from the third-wave folk, but rest assured the consistent and uniform grind from the coffee shop’s high-quality, well-maintained burr grinder is worth the disdainful eye.

With some careful attention paid to those four variables when you make coffee you’ll be brewing your perfect cup in no time. It does take some practice, but keep at it and the ritual you develop will go a long way toward your ultimate enjoyment of the brew. And one last piece of advice: when you’re cup is ready, before your add your cream and sugar, give it a stir, take a sip, and be present in the moment when the dark liquid gold washes over your taste buds, organic acids explode with flavor on your tongue and volatile oils seep up into your olfactory system. Take just one moment to stop thinking, stop doing, stop moving, and just taste the coffee. 


Joseph Meehan is a copywriter at Huckberry who would still be in bed were it not for the allure of the morning cup. He lives in Oakland, California. Follow him on Instagram for bad puns and good eats. 

Graph courtesy of The Conversation. Used under Creative Commons license. 

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