Roasting

Coffee Fundamentals

Course 1 · Chapter 4 · Roasting: Heat, Cracks and Roast Levels

Why Roast?

The dry green seed from chapter 3 has little of the smell or taste we call coffee. Roasting supplies it. Wikipedia's Coffee roasting article says that sugars caramelise, that Maillard and other reactions produce the roast flavour, and that chlorogenic acids break down, which it calls a key goal of roasting. The beans lose about 15 to 18 percent of their mass, mainly water, and their volume roughly doubles as vaporised water raises the pressure inside.

The Stages

The article describes a sequence you can hear. Early roasting absorbs heat (it is endothermic), but at around 175 °C it turns exothermic and the beans begin heating themselves, so a roaster has to manage the heat carefully rather than just keep adding it.

Stage	Approximate bean temperature	What happens
Drying	About 165 °C (image caption)	Water is driven off; the green seeds turn yellowish (check)
First crack	About 196 °C	After several minutes the beans "pop or crack"
Second crack	About 224 to 225 °C	A few more minutes later; oils start to surface on darker roasts

Two figures for one event

The article's text gives about 224 °C for second crack and its table gives 225 °C, and it does not reconcile them. I treat the difference as rounding. Chapter 1 quoted the Coffee article saying roasting begins when the bean's internal temperature reaches about 200 °C; the roasting article puts first crack at about 196 °C. These describe different moments (start of roasting versus first crack), and I have not found a source that lines them up (check).

The article gives no total roast time, saying only that first crack comes "after several minutes" and second crack "a few more minutes" later. Real roasting profiles are not covered by the page I read (check).

Roast Levels

Roast names are traditional and not standardised across roasters; the article lists these names against bean temperature.

Level	Bean temperature
Cinnamon	196 °C
New England	205 °C
American	210 °C
City	219 °C
Full City	225 °C
Vienna	230 °C
French	240 °C
Italian	245 °C

The article notes that its Roasts section is flagged as needing more citations, so treat these numbers as typical, not exact (check). Light roasts keep higher acidity; acidity is muted at medium-dark levels and nearly eliminated at the Italian roast. Lipids liquefy and can surface as oil, more so on darker roasts.

Code: Naming a Roast and Tracking Weight Loss

The script below looks up the highest level whose temperature has been reached, and works out roasted weight from the 15 to 18 percent loss. I ran it to get the output shown.

LEVELS = [("Cinnamon", 196), ("New England", 205), ("American", 210), ("City", 219),
          ("Full City", 225), ("Vienna", 230), ("French", 240), ("Italian", 245)]

def roast_level(temp_c):
    name = "Before first crack"
    for label, t in LEVELS:
        if temp_c >= t:
            name = label
    return name

for t in (190, 200, 212, 226, 244, 250):
    print(f"{t} C -> {roast_level(t)}")

for loss in (0.15, 0.18):
    print(f"1000 g green -> {1000 * (1 - loss):.0f} g roasted ({loss:.0%} loss)")

print(f"250 g roasted needs about {250 / 0.85:.0f} to {250 / 0.82:.0f} g green")

# Output
C -> Before first crack
C -> Cinnamon
C -> American
C -> Full City
C -> French
C -> Italian
g green -> 850 g roasted (15% loss)
g green -> 820 g roasted (18% loss)
g roasted needs about 294 to 305 g green

What the output shows

The lookup is a step function: a bean at 212 °C is "American" because it has passed 210 but not 219. And to end up with 250 g of roasted coffee you must start with roughly 294 to 305 g of green, since 15 to 18 percent is lost. The exact loss depends on the roast and the batch, which the article does not detail (check).

Caffeine, Density and Scoops

Caffeine is stable up to 200 °C and decomposes around 285 °C, which roasting rarely reaches, so roasting changes caffeine content little. This matches chapter 1. By volume, though, a lighter roast holds more caffeine than a darker one because darker beans are less dense. Measuring by weight removes the difference, which is why chapter 1 recommended it.

After the Roaster: Degassing and Freshness

Roasted coffee gives off carbon dioxide. Coffee that will be vacuum-packed has to degas for several days first; valved bags or pressurised canisters allow faster packaging. The article gives an optimal shelf life for roasted coffee of about two weeks and for ground coffee about 15 minutes. It also says whole roasted beans can stay fresh up to a month if kept cool, but that claim is marked "citation needed" on the page, so I treat it as unconfirmed (check). Green coffee can be stored about 12 to 18 months in a climate-controlled setting before quality loss is noticeable.

Home roasting

The article says home roasting means roasting small batches for personal use, was more common than buying roasted coffee after 1900, faded as commercial roasters grew, and has revived recently. Its stated motives are some economic advantage but mainly finer control over quality and flavour. I have not covered home-roasting equipment here (check).

Not Yet Verified, and Sources

Sources. Wikipedia article Coffee roasting, plus the Coffee article quoted in chapter 1.
Conflicts. Second crack is given as both 224 and 225 °C on the same page; the "roasting begins about 200 °C" statement in the Coffee article does not match the roasting article's first crack at about 196 °C, though they may describe different moments. Not resolved.
Weak support. The roast-level table sits in a section flagged for missing citations, and the one-month freshness claim is marked "citation needed".
Not in the page read. Total roast time, roast colours, the change of colour during drying, and degassing duration beyond "several days" (all marked check).
Not tested. The script is arithmetic and a lookup only; I did not roast anything.

Exercises

Exercise 1

Put these in order of increasing temperature and say what happens at each: first crack, drying, second crack, the point at which the process becomes exothermic.

→ Solution

Exercise 2

Use the script to name the roast level at 207, 222 and 235 °C. Then add a line that works out how much green coffee you need for 400 g of roasted coffee at the 15 percent and 18 percent loss figures.

→ Solution

Exercise 3

A friend says a dark roast has "much less caffeine". Using the chapter, explain when that is roughly true and when it is not, and what you would do to compare fairly.

→ Solution

Quick Reference

Mass loss: about 15 to 18 percent; volume roughly doubles
Exothermic from: about 175 °C; first crack about 196 °C; second crack about 224 to 225 °C
Levels: Cinnamon 196, New England 205, American 210, City 219, Full City 225, Vienna 230, French 240, Italian 245 °C
Caffeine: barely changed by roasting; less per scoop in darker roasts
Freshness: roasted about two weeks optimal; ground about 15 minutes

Coming next

Coffee Fundamentals 5 turns to grinding.