What Is Rate of Rise (RoR)?
There are two main ways to describe how the temperature of your beans is changing during roasting: bean temperature curve and rate of rise.
The bean temperature curve measures the actual temperature of your beans. It will look a little bit like a check mark.
RoR, however, is the speed at which the temperature of your beans is increasing. It’s measured over a specific period of time, usually between 30 and 60 seconds. Jen recommends using a 30-second period, advising that it will allow you better control. Say you have a RoR of 5 in 30 seconds: that means that your bean temperature is increasing by 5 degrees every 30 seconds.
RoR will also have a very different shape on the graph to your bean temperature curve. Jen tells me that, at the beginning of the roast (the drying phase), there will be a decrease in temperature causing a negative RoR. This decrease will eventually stabilise as the drum temperature and the bean temperature meet (causing the turning point). At this point, you will start to get a positive RoR.
So why measure RoR? Why not just use the bean curve? Because RoR gives much earlier indications of temperature developments. This enables you to better manipulate the roast and create your desired profile.