Coffee: Roast Curves — Charge Temp, Rate of Rise, and Profile Parameters
A standard coffee roast curve begins with charge temperature 180–200°C, turning point at 60–90 seconds (~80°C), mid-roast rate of rise 8–12°C/min, first crack, development phase, and drop.
| Measure | Value | Unit | Notes |
|---|---|---|---|
| Charge temperature (drum) | 180–200 | °C | Preheat temperature before loading beans |
| Turning point temperature | 75–95 | °C | Lowest bean temp after charge; typically at 60–90 seconds |
| Turning point time | 60–90 | seconds | |
| Peak RoR (early Maillard) | 12–16 | °C/min | |
| Mid-roast RoR target | 8–12 | °C/min | |
| RoR at drop (light roast) | 4–6 | °C/min | |
| Typical total roast time (drum) | 8–15 | minutes |
A roast curve is the graphical representation of bean temperature over time during the roasting process. Modern specialty roasters use logging software — primarily Cropster and the open-source Artisan Roaster Scope — to record and analyze curves in real time. Understanding curve anatomy enables repeatable, deliberate roasting.
Key Roast Curve Waypoints
| Waypoint | Typical Value | Notes |
|---|---|---|
| Charge temperature | 180–200°C | Drum preheat before loading beans |
| Turning point temperature | 75–95°C | Lowest recorded bean temp post-charge |
| Turning point time | 60–90 seconds | Earlier = hotter charge; later = cooler |
| Peak RoR | 12–16°C/min | Early Maillard phase |
| Mid-roast RoR | 8–12°C/min | Steady decline through Maillard |
| First crack onset | 196–200°C | Exothermic; RoR inflection point |
| RoR at drop (light) | 4–6°C/min | Smooth declining curve |
| Drop temperature (light) | 196–205°C | Bean internal temp at discharge |
| Drop temperature (dark) | 225–230°C | Post-second crack territory |
Charge Temperature
The charge temperature is the drum temperature at the moment green beans are loaded. It is the highest temperature in the roast curve for most profiles. A higher charge temperature means more thermal energy is available to drive moisture out of the bean quickly, resulting in faster early progression. A lower charge temperature produces a slower, gentler ramp. Charge temperature is calibrated based on batch size, roaster drum mass, and the desired total roast time. Typical drum roasters are charged between 180°C and 200°C for batches of 1–12 kg.
The Turning Point
After the cold beans are loaded into the hot drum, the bean probe temperature drops sharply as the cool mass absorbs heat from the drum environment. The turning point is the minimum temperature the bean probe records — typically 75–95°C — before the curve reverses direction and begins climbing. It occurs at approximately 60–90 seconds after charge. A very early turning point (before 60 seconds) indicates the charge temperature was high relative to batch size. A late turning point (after 90 seconds) may indicate under-charging or a cold environment.
Rate of Rise (RoR)
Rate of rise is the derivative of the bean temperature curve — the speed at which temperature is increasing, measured in °C per minute. It is the most analytically important parameter on the roast curve.
| Roast Phase | Typical RoR | Interpretation |
|---|---|---|
| Early (post-turning point) | 12–16°C/min | Fast climb through drying |
| Mid-roast (Maillard) | 8–12°C/min | Controlled, declining slope |
| Pre-first crack | 5–8°C/min | Deceleration into crack |
| Development phase | 3–6°C/min | Smooth, declining finish |
A well-designed RoR curve is smooth and continuously declining from its peak shortly after the turning point through to the drop. A RoR that crashes (drops steeply toward zero) and then recovers — sometimes called a “crash and flick” — is associated with baked, flat cup profiles regardless of the final bean temperature or DTR.
The “Flick” and “Baked” Coffee
If a roaster applies excess heat in the final minutes of the roast to push the bean temperature higher quickly, the RoR curve will show a late uptick — a “flick.” This indicates that heat application was non-uniform, with a suppressed middle section followed by an aggressive end. Experienced tasters can often detect the resulting baked character as a muted, stale, or cardboard-like note in the cup. The ideal RoR curve continuously and smoothly declines throughout development.
Roast Logging Software
| Software | Platform | Key Features |
|---|---|---|
| Cropster | Web-based, cloud | Commercial standard; device integration; analytics |
| Artisan Roaster Scope | Open-source desktop | Free; supports 100+ roaster brands; community |
| Ikawa Pro | Mobile (Ikawa only) | Proprietary; sample roaster workflow |
| RoastLog | Web-based | Inventory + roast logging combined |
Cropster dominates commercial specialty roasting due to its cloud-based batch comparison, blend tracking, and direct integrations with Probat, Loring, Diedrich, and other major drum roasters.
Curve Anatomy for Repeatable Results
A documented roast curve allows roasters to repeat, compare, and iteratively improve profiles. By anchoring key waypoints — charge temp, turning point, first crack onset temperature and time, DTR, drop temperature — and comparing them against cupping scores, roasters can build a data-driven understanding of what produces the best cup from each origin and lot. Batch-to-batch consistency depends on consistent charge temperature, batch weight, ambient conditions, and equipment maintenance.