Rate of Rise
The rate of rise describes the rise of temperature per 20, 30, or 60 seconds along a roast curve.
The level of gas and burner performance will either accelerate or slow down the rate of rise. During the roast, the level of air flow that pulls hot air from the burner through the roast drum also has an impact on the rate of rise.
After the turning point, which happens approximately within one minute into the roast session, the rate of rise goes up strongly. In a typical roast curve, the peak of the rate of rise is achieved in the first 2-3 minutes of the roast. From there it goes down continuously.
The art of roasting involves managing the energy levels and rate of rise in such way that all elements of the coffee will be developed at the different roast stages. A drastic drop in the rate of rise is just as undesirable as stalling it, which ends up baking the coffee beans.