Part II · Anatomy of a roast

Rate of Rise (RoR)

If you watch only one thing on a roast graph, watch this. Rate of Rise is how fast the bean's temperature is climbing right now — and its shape tells you more about a roast than the temperature ever will.

What it is

Rate of Rise is simply the change in bean temperature per unit of time — degrees per minute (sometimes per 30 seconds). Mathematically it's the slope of the temperature curve: steep curve, high RoR; flattening curve, falling RoR. If calculus is in your toolkit, RoR is the derivative of bean temperature.

Why obsess over the slope instead of the temperature? Because two roasts can pass through the exact same temperature at the same minute and taste completely different depending on how they got there. The rate is where the craft lives.

RoR should almost always fall

A healthy roast has a RoR that starts high and declines steadily to the drop. There's real physics behind that:

  • Early on, a cool bean sits in much hotter air — a big temperature gap means fast heat transfer, so RoR is high.
  • As the bean warms, that gap shrinks, so the same heat moves across more slowly.
  • Meanwhile the bean is spending energy boiling off water.

So a gently decaying RoR is the natural state of things. A RoR that stays flat — or worse, rises — means you're force-feeding heat, and the back half of the roast will fight you for it. The goal isn't a particular number; it's a smooth, steady decline.

Interactive

RoR Explorer

Shape the bean-temperature curve on top by dragging the dots; the Rate of Rise (its slope) is drawn underneath. Try the presets to see what a crash, a stall, and a too-hot start look like.

The two villains: crashes and flicks

Watch what the presets do to the blue line, because these are the faults roasters spend years learning to avoid:

  • Crash — the RoR suddenly plunges, sometimes below zero, often right around first crack as the bean briefly absorbs a burst of energy. A crash tends to taste flat, hollow, baked.
  • Flick (or "flip") — after a crash, the RoR rebounds back upward. The crash-then-flick combo in the development window is the single most chased-after fault in modern roasting, blamed for muddy, smeared flavor.

Both are symptoms of an unstable energy balance at the worst possible moment — just as the bean turns exothermic and you most need control. A smoothly declining RoR is, more than anything, a sign that you're managing that balance well.

Reading RoR on a real machine

  • Roasting software — Kaffelogic Studio included — calculates and plots RoR for you from the bean probe, in real time and on your saved logs.
  • RoR is noisy: taking a slope amplifies every little wobble, so software smooths it. Don't over-react to tiny bumps — read the overall trend.
  • Because your Nano follows a designed profile, a clean declining RoR is something you build into the profile rather than wrangle by hand mid-roast. More on that in Part IV.
🔑
Don't chase a number — chase a shape.

A smooth, steadily declining Rate of Rise that crosses first crack without crashing is the target on any roaster. Everything else — phases, development, the drop — is in service of keeping that line well-behaved.

Speaking of the drop: how do you know when to pull the trigger? That's development.