How does the bean temperature change during coffee roasting? The function of the throttle

There are two main ways to describe how the bean temperature changes during baking: the bean temperature curve and the rising rate. The bean temperature curve is used to determine the actual temperature of beans. It looks a bit like a check mark.

RoR, however, measures the rate at which the temperature of coffee beans rises. This is measured over a specific period of time, usually between 30 and 60 seconds. For example, you can choose a 30-second phase, and it is recommended that you choose a well-controlled stage. If you have an ROR of 5 in 30 seconds, it means that the temperature of your beans will increase by 5 degrees every 30 seconds.

ROR curve in the chart, compared with the bean temperature curve, will show a very different linetype. At the beginning of baking (dehydration period), the air temperature will show a negative growth rate, but the furnace temperature and bean temperature will eventually neutralize, which is what we call the temperature recovery point. From here on, your ROR will begin to show an upward trend.

So, why measure RoR? Because RoR can alert you to the rising trend and pattern of temperature in advance, you can more boldly manipulate and modify the parameters of baking according to this curve, and help you show the flavor you want through these adjustments.

A high ROR value indicates that the baking process is progressing faster; low means that it is progressing slowly.

Don't let your ROR fall too low, because you may reach the stall point. Stall roasting will occur when the ROR value is extremely low, that is to say, it may be 0 or negative, and the machine does not recover, and the temperature will remain the same, so that the coffee will only have roasted aroma and nothing else. It will also reduce the sweetness of coffee beans, resulting in a flat flavor of coffee beans. In this case, it is impossible to stimulate the compounds in coffee beans that can shape the flavor of coffee.

In the process of baking, the baker's goal is to accurately control the development of the RoR value. In the process of learning, you will find that when you are baking, you can make your coffee highlight a different flavor. For example, high RoR values, especially in the early stages of roasting, highlight the acidity of coffee.

The use of the throttle is to control the air flow and velocity in the boiler.

It is generally achieved by adjusting the opening of a baffle at a certain position of the smoke pipe installed in front of the exhaust fan of the roaster, or some roasters are achieved by adjusting the speed of the exhaust fan.

The size of the throttle will affect the effect of hot air in the boiler on the heating of coffee beans. Under the premise of sufficient heat, slightly increasing the throttle can enhance the effect of hot air on coffee beans, but if the heat is not enough or the throttle is too large, the boiler will lose temperature. Opening the throttle when necessary can more quickly remove the silver skins and particles that make the coffee smell. The size of the throttle will also affect the pressure of the boiler and the development of coffee beans.