The Coffee Field Guide

Tall and low-yielding, with very good quality at high altitude. Seeds reached Java in the late 1690s, a plant went to Amsterdam in 1706, and its descendants spread across the Americas in the 1700s. Typica made up most of Central America's coffee farms until the 1940s. Weak against leaf rust.

French missionaries took it from Yemen to Bourbon Island (now La Réunion) in the early 1700s, and it reached Brazil around 1860. Tall, medium yield, very good quality at altitude, weak against rust. Its own offspring, like Caturra and Catuaí, have mostly replaced it.

Found on a Brazilian farm between 1915 and 1918. Being compact means more trees per acre, so it spread through Central America after the 1940s. Rust-susceptible.

Crossed in Brazil in 1949 and released in 1972. World Coffee Research calls its cup "good but not great," and it's very susceptible to rust.

Found in Brazil in 1943 and widely grown there and in Peru.

Found in 1949 on the Pacas family farm in Santa Ana. It makes up roughly 25% of El Salvador's coffee.

Found near Maragogipe, Brazil, in 1870. A single gene makes the beans, leaves and everything else oversized.

Bred in El Salvador. Very large beans, low yields, and a frequent name at the top of El Salvador's Cup of Excellence. Very susceptible to rust.

Selected by Scott Agricultural Laboratories in Kenya: SL28 in 1935 from drought-tolerant stock, SL34 in the late 1930s. World Coffee Research rates both exceptional in quality at high altitude. Both are weak against rust.

Collected in Ethiopia in the 1930s, it moved through Tanzania and Costa Rica and reached Panama in the 1960s. In 2005 a Panama farm entered it in a competition and it set auction records. Known for jasmine and peach-like aromas.

Most Ethiopian coffee is local landraces shared between neighbors, plus selections from the Jimma Agricultural Research Center with numbers like 74110 and 74112. Bags often say "heirloom," which researchers call an oversimplification. Ethiopia holds most of arabica's genetic diversity.

Released in 2005 by Colombia's coffee research center, Cenicafé. It's become one of Colombia's most planted varieties, and cupping trials found no significant difference between its average scores and Caturra's.

Developed after coffee berry disease destroyed half of Kenya's crop in 1968. Ruiru 11 (1985) is compact, highly rust-resistant and very high-yielding. Batian (2010) is tall, resists coffee berry disease and has very good quality potential.

Crosses of two genetically distant parents. Centroamericano, released in Central America in 2010, is highly rust-resistant and yielded 22 to 47% more than standard varieties in trials. Their seeds don't grow true, so farms plant clones.

A pointy-seeded Bourbon mutation, reported at a small fraction of regular arabica's caffeine. Low yields keep it rare.

Machines strip the skin and pulp, then the seeds sit in tanks while microbes break down the sticky layer called mucilage. Workers push the coffee through channels to scrub the rest off, and it goes out to dry.

Washed coffees taste clean and bright and let the origin and variety do the talking. Traditional washing can use around 40 liters of water per kilo of coffee; newer eco-pulping equipment uses a small fraction of that.

Whole cherries dry in the sun until they turn from red to brown to almost black, then the dried husk comes off in one go. Done well, on raised beds in thin layers, naturals taste sweet and fruity with a round body. Done badly, they taste fermented.

Yemen, Ethiopia and Brazil have done it for generations.

The skin and pulp come off, but some of the sticky mucilage stays on while the coffee dries. As a rough rule, yellow honey keeps about a quarter of it, red about half, black nearly all; the more that stays, the more complex and the riskier it gets.

No honey involved: the name is about how sticky the beans feel. Costa Rica made it famous, and Brazil does a close cousin called pulped natural.

Coffee is pulped, fermented overnight, washed and half-dried, then hulled out of its papery parchment while still wet. Indonesia's humidity makes that practical, because bare beans dry two to three times faster.

The result usually has heavy body, low acidity and earthy, herbal notes. It's a big part of why Sumatras taste like Sumatras.

In anaerobic fermentation, coffee ferments in a sealed tank with a one-way valve, often for longer than a standard fermentation, sometimes days. Carbonic maceration ferments whole cherries in sealed tanks for days or weeks.

Expect unusual flavors, from ripe berry and grape to cinnamon. A coffee processed with carbonic maceration helped win the 2015 World Barista Championship.

Heat drives the water out. Green coffee is about 10 to 12% moisture and finishes near 2.5%. When enough is gone, the beans turn from green to yellow.

Sugars and amino acids react and turn the beans brown, the same chemistry that browns a bread crust. Sugars start caramelizing a little later. This stage builds sweetness and much of the aroma, and how long it lasts changes the cup.

Steam and CO₂ crack the beans open with a pop like popcorn. The time from first crack to the end of the roast is called development: stop early for a light roast, keep going for medium or dark.

Second crack, a faster, quieter snapping, comes around 440 to 450°F, and oils start moving to the surface.

How hot the roaster is when the green coffee drops in. Keeping it the same batch after batch is basic roaster discipline.

Cold beans pull the temperature down when they go in. The moment it bottoms out and starts climbing again is the turning point.

How quickly bean temperature rises, say 10°F every 30 seconds. Most roasters want it falling steadily as the roast goes on.

Development time as a share of the whole roast. Roaster and author Scott Rao recommends roughly 20 to 25% for most roasts.

Roasters check color with tools like an Agtron, which reads how much light the coffee reflects. The SCA's color disks run from 95 (very light) to 25 (very dark).

Drum roasters heat the beans mostly through contact with hot metal. Fluid-bed roasters float them in hot air and usually roast faster. Roasters tend to describe drum roasts as sweeter and fuller, air roasts as very clean.

How much coffee is actually in your cup by weight. It's what you taste as strong or weak. The SCA's classic target for drip coffee is 1.15 to 1.35%; the rest is water.

The share of the grounds' weight that ended up in the cup. The SCA's classic sweet spot is 18 to 22%. Newer research from UC Davis found people's preferences spread wider than one box on a chart.

The SCA's Golden Cup ratio, about 1:18, and the one every King's Gambit hot recipe uses. Like it stronger? Add a gram or two of coffee next time.

The SCA's home-brewer standard is 90 to 96°C, about 195 to 205°F. A 2020 UC Davis study found that once strength and extraction were matched, brewing anywhere from 87 to 93°C (about 189 to 199°F) changed the taste very little.

A blade grinder smashes beans into a mix of dust and chunks, so the dust over-extracts while the chunks under-extract. A burr grinder sends every bean through once for even particles. Grind right before you brew: the aromas you want start escaping as soon as the bean is opened.

Filter coffee is about 98% water, so your water matters. The SCA's targets: clean, no chlorine, about 150 mg/L of dissolved minerals and a pH around 7. Some minerals help pull flavor; too few make coffee flat and sour, too many dull it and scale your machine. Skip distilled and softened water.

Fresh coffee is full of CO₂. Wet the grounds with about twice their weight in water and wait 30 to 45 seconds so the gas escapes and the water can reach every grain. A big bloom is a sign of fresh coffee.