Coffee roasting

Roasting is the step that turns coffee from an inedible green seed into something you can grind and drink. The seed goes into a hot drum or hot-air chamber, and over roughly ten to twenty minutes it dries out, browns, swells, and builds the aromatic compounds that everything else in this wiki — cupping scores, auction prices, brew recipes — is ultimately judged on.

Two physical changes are worth holding onto, because everything else follows from them. The beans lose 15 to 18% of their mass, almost all of it water, and their volume roughly doubles as trapped steam pushes the cell structure outward.¹ So a roasted bean is lighter and much less dense than the green one that went in.

Green coffee, by itself, tastes of almost nothing. Roasting is where flavour is created rather than merely preserved — but it is also where flavour can be buried, which is the whole argument behind the third wave’s preference for lighter profiles.

The two cracks

Roasters navigate by ear, not by clock. Two audible events divide the roast:

• First crack — at roughly 196 °C (385 °F), water inside the bean flashes to steam, the bean expands sharply, and the batch makes a loud popping sound like popcorn.¹² Nothing is properly “coffee” before this point. Light roasts are stopped shortly after it.³²
• Second crack — at roughly 224 °C (435 °F), the bean’s cell walls themselves begin to fracture, in a faster, drier, more staccato crackle.¹² Oils start migrating to the surface. Dark roasts are taken into or past this point.²

Both numbers are approximate. What a thermometer reads depends on where the probe sits, how the machine is built, and how dense the beans are, so two roasters can disagree by several degrees about the same event and both be right.

Light, medium, dark

Roast	Where it stops	What it looks like	What it tastes like
Light	Shortly after first crack	Light brown, dry surface, no oil	Highest acidity; fruit, floral, citrus, sometimes grassy. Origin character most intact
Medium	Past first crack, before second	Medium brown, still largely dry	Balance of origin and roast — caramel, nuts, chocolate alongside fruit
Dark	Into or past second crack	Dark brown to near-black, visibly oily	Low acidity, bittersweet, smoky, roasty; origin character largely gone

Sources: ³²⁴⁵

The oil is the single most reliable visual tell. It is not added, and it is not freshness — it is the bean’s own lipids pushed out through broken cell walls, which is why an oily surface means the roast went into second crack.¹⁴²

The older European naming scheme is finer-grained and maps onto the same continuum:¹

	Name	Temperature	Character
1	Cinnamon	196 °C (385 °F)	Very light; underdeveloped sweetness, toasted grain and grassy notes
2	City	219 °C (426 °F)	Medium brown; the common specialty roast, good for tasting origin
3	Full City	225 °C (437 °F)	Medium-dark; start of second crack, roast character prominent
4	French	240 °C (464 °F)	Dark brown and shiny with oil; little inherent aroma left
5	Italian	245 °C (473 °F)	Nearly black and shiny; burnt tones, acidity nearly eliminated

To verify — the light-roast temperature range in the research does not fit the first crack number

One roaster’s guide behind this note gives light roast an end-temperature range of 350–400 °F (177–204 °C), medium 410–430 °F, and dark 430–480 °F.³ The medium and dark figures sit comfortably against the named scale above. The light figure does not: first crack is 385 °F, so the bottom half of that “light roast” range would end the roast before first crack ever happens, which contradicts the same source’s own statement that light roasts stop shortly after it. Either the range is loosely drawn or it is measuring something other than bean temperature. Treat published °F ranges for “light” as indicative only; the crack milestones are the reliable landmarks.

Nobody has defined these words

This is the most important thing on the page. There is no published standard for what “light”, “medium” or “dark” mean. One roaster’s medium is another’s dark, at physically identical roast levels.⁵⁴

That is not a gap in this note’s research — it is a gap in the industry. The Specialty Coffee Association, which publishes standards for cupping, descriptive and affective assessment, home brewers, grinders, espresso machines and training venues, lists SCA-131 Coffee Roast Level among the standards still under review and development, not among those published.⁶ Until that lands, roast level is a marketing word, not a measured one.

The same applies to the newer descriptive labels — “Nordic light”, “third-wave light”, “omni-roast”. They describe real practices, but none of them carries a defined threshold.⁵⁴

Measuring roast colour instead of guessing

The workaround is to stop using words and measure the coffee’s colour with a colorimeter — an instrument that shines light at ground coffee and reads how much bounces back. Darker roasts absorb more light and reflect less, so a single reflectance number can stand in for the whole vocabulary problem. The best-known instrument scale in the trade is the Agtron scale, and readings from different instruments are not interchangeable.

To verify — the reflectance figures found in research run backwards

A roaster’s blog consulted directly here gives colorimeter values of 65–70% for a Nordic light roast, 72–76% for medium, and about 85% for a French dark roast, and states explicitly that higher reflectance means darker.⁵ That is the opposite of how reflectance works physically — a darker surface reflects less light, not more — and the opposite direction to the way roast-colour instrument numbers are conventionally read, where a high number means a light roast. No standards body or instrument maker was reachable to settle it, and the SCA has no published roast-level standard to check against.⁶ Do not quote these numbers; the direction of the scale is in doubt, so the values may be mislabelled.

Phases and “development”

Roasters usually split the roast into three stretches:⁷

• Drying — from the moment the green beans hit the hot drum until they have shed most of their free moisture and turned from green to yellow.
• Browning — from yellowing to first crack. This is where the Maillard reaction runs: amino acids and sugars recombine under heat into brown pigments and hundreds of flavour precursors, the same chemistry that browns bread crust and seared meat.²⁴
• Development — from first crack to drop (the moment the beans are dumped out to cool). Caramelization and pyrolysis take over from Maillard, precursors become finished aromatics, and roast level is set.²⁷⁴

“Development” is the word roasters argue about most. Underdeveloped coffee — dropped too soon after first crack — tastes grassy, sour and thin no matter how good the green was, and it is the standard failure mode of chasing light roasts. Overdevelop and you flatten the origin character you were roasting lightly to protect.

To verify — the development-time numbers circulating are practitioner folklore, not standards

Several widely repeated figures appear in the research behind this note and rest on a single forum thread of roasters comparing notes:⁸ that roast time should split roughly 50% drying, 30% browning, 20% development; that development should be 16–25% of total roast time, with one roaster targeting about 18%; and that 14–16% weight loss marks a “pretty light” roast. A practical guide separately suggests dropping 1–1.5 minutes after first crack for light, 1.5–2.5 minutes for medium, and after second crack begins for dark.⁷ None of this is a standard. It varies with machine design, charge temperature, batch size and bean density, and the 14–16% weight-loss figure also sits just below the 15–18% general range given by the more authoritative source here.¹ Useful as orientation, not as a target to be held to.

What roast level does downstream

• It decides how much origin survives. Light roasting is the reason a bag can meaningfully claim a farm, an altitude, a process and a variety — those differences are audible in the cup at light roast and largely inaudible at dark. Dark roasting makes coffees taste like each other. This is precisely why the third wave roasted lighter, and why Specialty coffee grades the green and the cup rather than the roast.
• It changes how the coffee brews. Darker beans are more porous and less dense, so they give up solubles faster; that shifts grind, dose and contact time, and moves where a recipe lands on Extraction yield and Brew ratio.
• It shifts the acid–bitter balance. As roast level climbs, perceived acidity falls and bitterness rises — the same way caramel gets more bitter the darker you take it.³⁴⁵

Roasting also builds the aromatics that make the cup complex at all: over 800 volatile aromatic compounds develop across a full roast.⁵

The caffeine question

The persistent café myth is that dark roast is stronger in caffeine. It is not, and the reason is density rather than chemistry.

Caffeine is thermally stable up to about 200 °C (392 °F) and only decomposes completely around 285 °C (545 °F) — well past where any drinkable roast ends.¹ So roasting barely destroys it, and gram for gram, light and dark roast contain effectively the same amount.⁵⁴

What changes is the bean. Darker beans lost more water and expanded more, so they are less dense. Measure by scoop rather than by scale and the lighter roast packs more mass — and therefore more caffeine — into the same volume.¹⁵

To verify — the size of the caffeine gap

The figure repeated in the research is that the difference runs roughly 5–15% in either direction, depending on the coffee, the roast and the measurement method.⁵⁴ That comes from roaster and educator summaries, not from a published lab assay traced here. The direction is well supported — light roast wins by volume, the two tie by weight — but treat the percentage as an estimate. Note also that the largest caffeine differences in coffee come from species, not roast: see Arabica vs Robusta.

Related

• Third wave coffee — the movement that made lighter roasting a signature, and the reason “roasted light” became a selling point
• Specialty coffee · Coffee scoring · Cupping · Coffee Value Assessment — how coffee is graded, all of it downstream of a roast decision
• Specialty Coffee Association · Q Grader — the body drafting a roast-level standard, and the licence for scoring the result
• Coffee roasting profiles — the curve itself: bean temperature against time, rate of rise, and the development time ratio this note leans on
• Agtron scale · Maillard reaction — the instrument and the chemistry this note leans on
• Loring Smart Roast — a roasting machine maker whose single-burner design and 2026 purchase of the ColorTrack colour meters bear directly on the fuel and roast-colour questions above
• Sample roasting — the tiny, deliberately plain test roast used to judge green coffee rather than to make it taste good
• Coffee freshness and degassing — what happens to the beans in the days after they leave the drum, and why darker roasts need less rest
• Extraction yield · Brew ratio · Total dissolved solids — what a roast level does to a brew recipe
• Washed process · Natural process · Anaerobic fermentation — the origin character a light roast is trying to keep
• Arabica vs Robusta · Fine Robusta — where caffeine differences actually come from
• Japan coffee market — a large market where dark roasting held on long after specialty went light
• Scott Rao — the consultant and author whose self-published books are the standard written reference for roast practice

Official links

• Official site — Specialty Coffee Association, Coffee Standards

Footnotes

1. Coffee roasting — Wikipedia — confirmed via WebFetch; source of the 196 °C/385 °F and 224 °C/435 °F crack temperatures, the 15–18% mass loss, the doubling of volume, the Cinnamon-to-Italian named scale, and the caffeine stability thresholds ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Coffee Beans AU — Understanding Coffee Roast Levels: Light, Medium, and Dark — cited via the research report; source of the crack descriptions, oil migration and roast-phase chemistry ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

3. Peach Coffee Roasters — A Guide to Coffee Roasts: Light, Medium, and Dark — cited via the research report; source of the °F end-temperature ranges ↩ ↩² ↩³ ↩⁴

4. Peet’s Coffee — An Intro to Coffee Roasts — cited via the research report; source of the non-standardised naming point, the acidity/bitterness trend, and the caffeine-by-weight equivalence ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

5. Jayarr Coffee — Coffee Roast Levels Explained — confirmed via WebFetch; source of the disputed colorimeter reflectance figures, the 5–15% caffeine range, and the 800+ volatile aromatic compounds ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

6. Specialty Coffee Association — Coffee Standards — confirmed via WebFetch; source of the published standards list and of SCA-131 Coffee Roast Level being listed as under development rather than published ↩ ↩²

7. Rubasse Roasters — Super Basic Coffee Roasting: How to roast light, medium, dark roasts — cited via the research report; source of the three-phase model and the minutes-after-first-crack guidance ↩ ↩² ↩³

8. r/roasting — Development Time Question — cited via the research report; a forum discussion, and the sole source of the 50:30:20 split, the 16–25% development ratio and the 14–16% weight-loss target ↩