Everything you taste in a cup of coffee is decided twice — once by nature, in the green bean, and once by you, at the roaster. Book 2 starts where the roast really starts: inside the seed.
Most roasting problems don't begin at the roaster. They begin earlier — in green coffee that was never properly understood before it hit the drum. Part 1 of The Roasting Bible Book 2 is the foundation the entire science rests on: what a green bean is actually made of, how its physical structure governs the way heat moves through it, how origin and terroir set the ceiling on flavour, how processing rewrites the bean's chemistry, and finally how to read all of that before you commit to a profile.
If Book 1 taught you to roast, this part of Book 2 teaches you to predict. Once you can look at a lot of green coffee and anticipate how it will behave, roasting stops being guesswork and becomes strategy. Here's a tour of what those first four chapters and the green-evaluation supplement cover.
Inside the Book — Part 1
Chapter 1 — Chemical Composition of Green Coffee
Chapter 2 — Physical Properties and Their Impact on Roasting
Chapter 3 — Origin Chemistry: How Terroir Affects Roasting
Chapter 4 — Processing Methods: How Fermentation Shapes Flavour
Supplement S1 — Green Coffee Pre-Roast Evaluation (new in the 2nd edition)
Chapter 1 — The Warehouse Inside the Bean
What Green Coffee Is Actually Made Of
A coffee bean is a seed, and nature packed it with intent — sugars to fuel growth, oils to carry energy, proteins, acids, and a cellulose skeleton to hold it all together. Book 2 frames it as a tightly packed warehouse: "Roasting is what happens when you set fire to that warehouse in a controlled way. What burns first, what melts, what transforms — that sequence determines everything you taste in the cup."
Green coffee holds roughly a thousand compounds, but only about a hundred are concentrated enough to change how a bean roasts and tastes. Chapter 1 walks through the major classes by dry weight: cellulose and fibre (30–35%), oils (15–17%), proteins and amino acids (10–12%), water (10–12%), chlorogenic acids (6–8%), and sugars (6–10%). Each has a job. Cellulose is the skeleton; lipids carry aroma and build body; chlorogenic acids start harsh and mellow into complexity; water is the conductor that controls timing and pressure.
If one idea carries the chapter, it's that sugars are the fuel for nearly everything you taste. Sucrose — around 6–9% of an Arabica bean by dry weight — breaks under heat into glucose and fructose, which then react with amino acids in the Maillard reaction to create browning, sweetness, and the hundreds of aromatic compounds that make coffee taste like coffee. That single fact explains a lot: high-altitude Ethiopians and Kenyans, often carrying 8–9% sucrose, simply have more fuel to spend than a lower-altitude lot at 6–7%.
Key idea: More starting sugar means more potential sweetness and complexity. It's a major reason high-altitude coffees so often taste sweeter — they literally have more to work with.
Chapter 2 — The Container
Why Two Beans Roast Differently
Chapter 1 covered what's inside the bean. Chapter 2 covers the container those chemicals live in — and here's the part that surprises new roasters: two beans with identical chemistry but different physical properties will roast completely differently. The book's analogy is cooking two steaks, one thick and one thin: same meat, same seasoning, but the thick one needs lower heat and more time or you char the outside while the centre stays raw.
Density is the master variable. A dense, high-altitude bean is the thick steak; a porous, low-altitude bean is the thin one. Heat travels through a dense bean "like a car driving through traffic — slowly, with resistance," and through a porous bean "like a car on an empty highway." That difference compounds over an 8–12 minute roast, which is why dense beans are more prone to a scorched surface over an underdeveloped core if you charge too aggressively.
Alongside density, the chapter covers the other physical signals that shape a roast: moisture (every percentage point translates directly into roast time and energy), screen size (mixed sizes roast unevenly), hardness, and colour or age. It also lays out how to measure density in practice — from the by-feel intuition of a bluish-green, heavy bean, through water displacement on the roastery floor, to pycnometer precision in the lab.
Key idea: If you could measure only one thing about a green coffee, measure density. It predicts roast behaviour better than almost anything else — dense beans want patience, porous beans want a faster, watchful hand.
Chapter 3 — Terroir
How Origin Sets the Ceiling
Every green coffee arrives with a flavour ceiling — the maximum complexity, sweetness, and character it can express. The roaster's job is to get as close to that ceiling as possible, and origin chemistry tells you where the ceiling is. Chapter 3 covers the natural factors that shape the bean before anyone touches the drum: altitude, variety, seasonal effects, and storage aging.
Altitude is the single most reliable signal. Daytime temperature drops about 0.6°C for every 100 metres of elevation, so a farm at 1,800m ripens its cherries in markedly cooler air than one at 1,200m. Slower ripening lets the seed accumulate more sucrose and organic acids and build a denser cell structure — more potential, but also a bean that demands more careful roasting. Rush a high-altitude Ethiopian and you get sharp, underdeveloped sourness instead of bright, layered acidity; give a low-altitude Brazilian too much time and you bake out the very sweetness that makes it appealing.
Variety matters too, the way grape varieties do in wine. The chapter maps cultivars across a spectrum from delicate to robust — Geisha, with its jasmine-and-bergamot florals, is the most sensitive and rewards a very light touch; Bourbon and Typica, high in sucrose and balanced, are the tolerant workhorses that take a range of profiles. Aging rounds it out: properly stored green coffee holds for six to nine months, but after a year expect faded acidity and muted aromatics.
Chapter 4 — The Human Factor
How Processing Rewrites the Bean
If terroir is what nature gave the bean, processing is what people did with it between harvest and export — and it is one of the biggest variables in coffee chemistry. The book organises every method by a single question: what was added, and when? That yields four tiers, from traditional methods that add nothing, through controlled-environment ferments, to biological enhancement and direct flavour addition.
Washed coffees — depulped early and fermented briefly — give you the clean, transparent cup, the one where "what you cup is what you'll get, batch after batch." They're the most forgiving to profile and the best place to start with a new origin; the key is to develop them long enough to express the complexity locked in the seed, because underdeveloped washed coffee tastes sour and grassy.
Naturals are the opposite temperament. The whole cherry dries intact for weeks while wild yeasts metabolise fruit sugars into esters and acids that migrate into the bean — producing blueberry, strawberry, and a syrupy body no other traditional method matches. The trade-off is variability and risk: more chances for defects, more bean-to-bean inconsistency, and a need for careful sorting. As the tiers climb into anaerobic, carbonic, inoculated, and infused lots, the guidance shifts — shorter development for controlled ferments, and always blind-cupping the experimental ones before committing.
Key idea: Knowing which processing tier a coffee belongs to tells you the fundamental approach before you even charge the drum. Tier 1 is predictable; the higher tiers reward caution and a cupping spoon.
Supplement S1 — New in the 2nd Edition
The Conversation Before the Roast
The four chapters explain the theory; the green-evaluation supplement makes it a routine. Green evaluation, as the book puts it, "is the conversation you have with the bean before the roast begins." It takes 15–20 minutes per lot and answers two questions: is this coffee suitable to roast, and what does my profile need to change? Most roasting problems, the supplement argues, trace directly to green characteristics that were simply overlooked.
Moisture leads. Specialty Arabica should arrive at 10–12% — the baseline for reliable development. Above 12%, the drying phase drags and beans develop unevenly, so you raise charge temperature and extend the roast; below 10%, the coffee runs fast and over-develops on your existing profile, so you ease back. The supplement also introduces water activity, the metric your moisture meter doesn't show: two lots can both read 11% yet behave very differently, and an aw above 0.65 is reason to reject a lot for mould risk. It closes with practical storage — 10–15°C, 60–65% humidity, FIFO rotation — to protect quality for those six to nine usable months.
Who This Post Is For
Reading the Bean Before the Roast
If you've worked through Book 1 and want to understand why your roasts behave the way they do — or you're a working roaster who wants to stop being surprised by a new lot — Part 1 of Book 2 is where the science begins. It's for anyone ready to move from following a profile to predicting one.
Read the Full Book
Part 1 is the foundation of The Roasting Bible Book 2: The Science of Coffee Roasting — roughly 340 pages across seven parts, with six field-tested practitioner supplements added in the 2nd edition.
Get Book 2 (Digital Edition)Also available in paperback on Amazon KDP — search "The Roasting Bible Wing Yuen".
Written by Wing Yuen, SCA Authorised Trainer at Tasse Coffee Roastery in Shinjuku, Tokyo. The Roasting Bible is a two-book series: Book 1 for beginners (165 pages) and Book 2 for the science of roasting (~340 pages, 2nd edition).
