Coffee Roasting Essentials: A Guide to Rate of Rise (RoR)
Rate of rise (RoR): scroll through enough articles on coffee, and you’ll come across this mysterious term, complete with multi-line graphs that are frustratingly short on explanation. But RoR isn’t indecipherable.
And in fact, RoR is a valuable tool for any roaster, explaining what’s going on in the bean during roasting. In this way, it can help you to control your roast, avoid defects, and craft the best possible flavour profile for a coffee.
I had the opportunity to talk to Jen Apodaca, Director of Roasting for Royal Coffee and their upcoming project The Crown: Royal Coffee Lab & Tasting Room, about all of this. Read on to discover what I learned.
Jen Apodaca inspects beans during a roast. Credit: Royal Coffee
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.
Freshly roasted beans. Credit: Square One Coffee Roasters
HOW HIGH SHOULD YOUR ROR BE?
You’ll often hear people discuss a high or low RoR. And simply put, a higher RoR indicates that your roast is progressing quicker; a lower one means that it’s progressing slower.
Jen tells me that you don’t want your RoR to drop too low because then you risk reaching the stalling point. A stalled roast happens when the RoR becomes so low that the machine doesn’t want to recover, and the temperature remains the same. This can lead to “baked coffee”, a defect that creates a flat, doughy flavour. In this situation, the coffee’s aromatic compounds won’t be developed.
However, that doesn’t mean a high RoR is best. Your goal should be to control your RoR with precision. And as you learn how to do this, you will find you are able to accentuate different flavours in your coffee. For example, a higher RoR – especially towards the beginning of the roast – can accentuate acidity. Willem Boot of Boot Coffee and Finca La Mula also states that a lower RoR can help modulate sweetness.
The right RoR will depend on many factors: the coffee, the desired profile, the stage in the roast, and more.
Freshly roasted coffee cools before being packed. Credit: Alex Jones
TOP, CRACK, & END RATE OF RISE
Your RoR will change as the roast continues to develop, and there are certain moments that are worth paying more attention to. This includes top/max RoR, crack RoR, and end RoR, stages that professionals such as Patrik Rolf and Morten Münchow have highlighted as critical.
The top/max RoR is the stage after the turning point (remember, this is when the temperature stops dropping and starts increasing, meaning the RoR goes from negative to positive) when the RoR is at its highest.
The crack RoR is the temperature change during first crack. Some roasters struggle to prevent their bean temperature (remember, this is different from RoR) from dipping here, as a result of steam being released from the beans. While you want to avoid this dip, you also don’t want to increase the temperature as that could be too heavy-handed.
As for the end RoR, that is of course at the end of the roast. You want to be careful at this point in time, because the beans will be drier and therefore more brittle.
Coffee cools immediately after being roasted. Credit: Angie Molina
WHEN TO ADJUST YOUR RATE OF RISE
With RoR, there are certain “rules” which are good to follow. Most notably, Scott Rao makes the case for a steadily decreasing one. While stalling will create baked flavours, an increasing RoR – especially after first crack – can lead to a coffee that lacks sweetness.
Yet within these parameters, there is plenty of room for roast manipulation. Jen tells me that there are particular moments during the roast that are suited to adjusting your RoR. For example, the drying and yellowing stages provide you with plenty of time for temperature changes.
In contrast, she explains, “The crucial time is the minute or two before first crack, and right after. At that time, the choices you make can have many more consequences and you need to be very attentive.”
Coffee beans are inspected during roasting. Credit: Killer Roasting Co.
RoR may be a simple concept, but it opens the door to complex decisions about how you want to roast your coffee. Today, we’ve mainly looked at what it is and some general guidelines for controlling it.
And now, I’d encourage you to experiment with it. See how a higher RoR affects that sparkling Ethiopian. Try using an earlier max RoR – or a later one. Take notes. Compare the results across different coffees.
Embrace the impact that you can have on a coffee’s flavour profile – and how you can accentuate its best characteristics.