What Is Coffee?

Phenomenon

In a single day you might use the word "coffee" in five completely different senses.

The news says "coffee prices hit a record". A friend says "I saw coffee growing in Yunnan". A roaster's bag says "coffee beans, roasted last Tuesday". In the morning you say "I'd like a coffee". A sign in a botanical garden reads "Coffee, family Rubiaceae".

Is the "coffee" in those five sentences the same thing? A tree, a fruit, a sack of pale green seeds, a bag of brown beans, a cup of dark liquid — how are they related? And what happens between each one and the next?

Variables

Pull the word apart and you get five forms along one chain:

Between each pair of forms there is one action that turns the first into the second: growing, separating and drying, heating and dissolving. This chapter asks what each action takes away, what it leaves, and what it adds.

Experiment

Two thought experiments.

First: at a farm, you pick one kilogram of fully ripe coffee cherries and plan to take them all the way to a cup.

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How much green coffee will that kilogram of fruit become? After roasting, how much will be left? Compare them: cherries, green coffee, roasted coffee — which weighs the most, and which the least?

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Second: on the table are two small bowls with the same number of beans — one green, one roasted.

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With your eyes closed, using only your nose, could you tell which bowl is green? Will green coffee smell like coffee? If you drop a few of each into a glass of water, which kind sinks?

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Observation

From cherry to green coffee, most of the weight is taken away. A cherry is mostly water, skin, pulp and mucilage; the seed is only a small part of it. A common figure is that it takes about five to six kilograms of fresh cherries to make one kilogram of green coffee Confidence: [Rule of Thumb], depending on fruit size, ripeness and processing. How and when the rest is removed is what Chapter 7 calls "processing".

Green coffee is dry, but not without water. The International Coffee Organization's quality target for exported green coffee is a moisture content between 8% and 12.5% Confidence: [Common Practice]. Too wet and it can go moldy; too dry and it deteriorates and roasts less predictably (Chapter 12).

Green coffee does not smell like coffee. It smells more like grass, beans or hay. Almost all of the coffee aroma we know is created during roasting, by heat-driven chemical reactions Confidence: [Established Mechanism] whose raw materials are the sugars, proteins and acids stored in the seed (Chapters 2 and 13).

Roasted beans are lighter than green ones, and bigger. During roasting the beans lose water and some of their dry matter, while swelling and becoming porous Confidence: [Strong Evidence]. The darker the roast, the more weight is lost; a common figure is 10–20% lighter Confidence: [Rule of Thumb]. So a bowl holds fewer roasted beans, and the same number of roasted beans weighs less.

In water, green beans usually sink, and roasted beans usually float for a while. Roasted beans are full of pores and gas from roasting, which makes them lighter than water overall.

A cup of coffee is almost all water. In a cup of filter coffee, dissolved coffee material is usually only a little over one percent Confidence: [Common Practice]; the rest is water. Most of what was in the grounds — mainly insoluble plant fiber — stays in the filter (Chapters 22 and 23).

Model

One chain, four actions

Join the five forms and you have a chain from tree to cup. Each step is driven by one action:

1. Growing (plant → cherry): leaves make sugar from sunlight, and the plant stores some of it, along with other materials, in the seed (Chapter 2).
2. Separating and drying (cherry → green coffee): the fruit is removed, and the seed's moisture is brought down to a level where it can be stored and shipped (Chapters 7 and 12).
3. Heating (green → roasted): heat turns the seed's stores into color and aroma, and makes the bean brittle enough to grind and dissolve (Chapters 13 and 14).
4. Dissolving (roasted → cup): grinding exposes surface area, and water carries away a small soluble part of it (Chapters 19 and 23).

Each step can only use what the last one left

The chain has a direction: later steps can only work with what earlier steps left behind. A common way to put it: upstream sets how good a cup can be, and downstream decides how much of that is realized Confidence: [Rule of Thumb]. Roasting cannot create what was never in the seed, and brewing cannot create aroma the roast did not make.

That is only a starting point, though: every downstream step can also ruin what came from upstream. Good green coffee can be scorched, and good roasted coffee can be brewed badly (Chapter 23).

The further downstream, the less stable

The second pattern is stability. Green coffee keeps for months, up to about a year; roasted coffee changes noticeably within weeks; once ground, aroma is lost faster still; a brewed cup changes within tens of minutes Confidence: [Rule of Thumb]. That is why coffee crosses the world as green coffee, and roasting usually happens fairly close to the people who drink it (Chapter 17).

Which "coffee" do you mean?

Back to the five sentences at the start:

• "Coffee prices" usually means the international trading price of green coffee;
• "Coffee growing in Yunnan" means the plant, or the cherries on it;
• The "coffee beans" in the bag are roasted coffee, and the roast date is about its freshness;
• "A coffee" is the small part that dissolved;
• The botanical garden sign is about the plant itself.

One word, different positions on the chain. Once you know which position you mean, many questions point somewhere.

Transfer

Next time you read something about coffee, ask first which part of the chain it is about:

When a cup tastes wrong, walking back up this chain works better than changing a variable at random Confidence: [Rule of Thumb]: first ask whether it is a brewing problem or something about the coffee itself, then move upstream.

Misconceptions

"Coffee beans are beans." They are the seeds of a flowering tree. Coffee belongs to the madder family, Rubiaceae, not the legume family Confidence: [Established Mechanism]. "Bean" is just about the shape (Chapter 2).

"Coffee beans grow in pods, like peas." Coffee has no pods. The seeds grow inside a juicy fruit, wrapped in turn by skin, pulp, mucilage and a papery inner shell. So the first job is not "shelling pods" but "removing fruit".

"Coffee beans are naturally brown and already smell like coffee." A seed freshly taken from the fruit and dried is pale green or straw-colored and smells of grass. The brown color and the coffee aroma are both made by roasting.

"Green coffee is a dry good and never changes." Green coffee is far more stable than roasted coffee, but it is still a seed that was once alive. It holds moisture and slowly reacts with air, temperature and humidity. Kept too long, it loses some of its fresh flavor, and the trade says it has "aged" (Chapter 12).

Real Lab

There is no registered lab card for this chapter, but with a small handful of green coffee and a small handful of roasted coffee you can see most of the Observation section for yourself. Home-roasting suppliers sell green coffee, and you need very little.

1. Look. Lay out twenty of each side by side on white paper. Compare color, size and the slit down the middle.
2. Press. Push a fingernail into each. Which is harder? Can you snap a roasted bean?
3. Smell. Green first, then roasted. Write three words for each.
4. Weigh. (If you have a kitchen scale) weigh twenty of each; or fill the same small spoon with each and count the beans.
5. Soak. Drop a few of each into a glass of room-temperature water and see which sink and which float.

Finally, write the five forms in order on a sheet of paper. Between each pair, write the action, and the evidence you saw with your own eyes today.

Check Your Model

Predict. You buy one kilogram of green coffee and roast it to medium-dark at home. Roughly how much roasted coffee will you have? If you roast darker, more or less?

Diagnose. A friend says: "This bag is really fresh, roasted last week — although it says the green coffee was harvested two years ago." Is that a contradiction?

Explain. In your own words, explain why coffee is mostly shipped around the world as green coffee rather than as roasted beans or ground coffee.