About Rate of Rise (RoR)

This article explains what the RoR is, how it assists you and how it is calculated.

The Rate of Rise (RoR) is a core part of our roast logging and analysis tool Cropster Roast.

What is Rate of Rise (RoR)?

The RoR curve displays the current increase of the bean temperature over a time period called the time expression (for example 30 seconds or 60 seconds). RoR assists you in three different ways:

Roast speedometer (acceleration)

The RoR curve displays the increase (or decrease) in bean temperature over the time period given by the Time expression setting (in mathematical terms you can think of this as the derivative of the temperature curve). It is your real-time roast navigation system that supports you in roasting high quality coffee at a consistent level! 

To use an analogy, if you think of the bean temperature as the speed of a car, then the RoR gives you the acceleration of the car. High acceleration means the car is going faster and faster, acceleration of 0 means constant speed and negative acceleration tells you that the car is slowing down. 

So a high RoR tells you that the bean temperature increase is high. When the RoR starts to decline and gets closer to 0 the increase of bean temperature gets smaller and the bean temperature flattens. If the RoR is negative the temperature of the beans is decreasing, which you definitely want to avoid during the roast.

Roast track preview

The RoR reacts stronger and earlier to temperature changes than the usual bean temperature curve. When overlaying the reference RoR and the current RoR, you get a visible difference showing you if the coffee develops differently than the reference. You can see this difference 30-60 seconds before any visible change in the bean temperature. This gained time can be used to take corrective action. 

To use our car example again, if you expect obstacle along your way you don’t want your car to accelerate too quickly since then you may not be able to slow down in time. On the other hand if your car is not accelerating fast enough it will take forever to get to the desired speed (heat up the beans fast enough).

Heat development navigation

The RoR will highlight inconsistent heat development in a more pronounced way than the bean temperature curve. A bumpy RoR can be a sign of uneven heat development. This will affect aroma development so it is something that you want to be aware of. Bumps are stronger in the RoR than in the bean temperature, so it is more likely you will notice.

How Rate of Rise (RoR) is calculated and what changes with the new settings?

Throughout Cropster in both Roasting Intelligence (> RI 4.5) and our online platform, you can adjust what your RoR calculation (setting) is. The RoR now offers three different settings, Recommended (the default setting), Sensitive and Noise Smoothing. For all three settings the value of the RoR curve shows the temperature increase over a time span, how large this time span is can be adjusted with the Time expression setting. 

For example for the default Time expression of 60 seconds the RoR shows the temperature increase or decrease over the last 60 seconds. Changing the Time expression setting does not affect the shape of the Rate of Rise curve but only the unit of measurement (C˚/60s, C˚/30s, ...).

The Recommended setting offers the best balance between a smooth, interpretable RoR curve and a RoR which responds quickly to changes in the roast temperature. If you already use the RI4 Rate of Rise nothing will change for you since the recommended setting is the equivalent to this setting with only slightly enhanced smoothing to even out very small spikes in the RoR curve.

The Noise Smoothing setting can be used in case the RoR curve is hard to read due to probe noise when using the recommended settings. This setting is geared towards users who had difficulties switchingto the RI4 Rate of Rise calculation method because of spiky RoR curves. It is strongly recommended to inspect the temperature probes (see Isolating probes) to be able to use the Recommended setting, since the smoother Rate of Rise in this setting comes at the cost of a RoR curve which is less responsive to changes in the bean temperature development.

A solid, almost noise free roast machine setup with Recommended (Green) vs. Noise Smoothing (Purple) RoR settings.

The Sensitive setting gives a very responsive RoR curve, but depending on the setup the RoR can also be very shaky due to noise in the bean temperature measurements.

A solid, almost noise free roast machine setup with Recommended (Green) vs. Sensitive (Purple) RoR settings.

For more information check out our blog post