In addition to understanding the roasting situation through the senses, the temperature of the coffee beans is the basic indicator we come into contact with during the roasting process. We can use the bean temperature to understand where the coffee is on the roast cycle curve.
The temperature of the beans is critical, but it is also important to measure it with clocks and stopwatches. Time and temperature are everything.
The placement and cleanliness of the temperature probe can also affect the reading. This means we want to be careful not to overinterpret the bean temperature reading or compare it to readings collected from other roasters. There is also no standardized platform for interpreting roast data due to variations between roasters.
What we can do, however, is pay attention to the temperature reading, where we can learn about browning and caramelization (indicated by a slight decrease in the rate of rise) and the status of the first crack. With the temperature readings, we can also compare the temperature data to the observed reactions of the checkpoints in the roast. This will help us formulate subsequent roasting plans.
The main thing in roasting is to keep the readings consistent. From an accuracy standpoint, it doesn’t matter if the reading is technically right or wrong. It just needs to be consistent in the roast, there are no anomalies or discrepancies in that data.
Rate of Rise (RoR)
This reflects how the bean temperature changes. For previous generations of roasters, it was not possible to view this data in real-time. However, modern software such as Cropster allows us to track and react to the rate of heat rise while baking. Cropster software has probably become the single most important invention or technological advancement that our coffee industry has ever seen.
Since the ROR profile can tell us if the roast is speeding up or slowing down, it can give us insight into the future of the bean temperature profile. That is to say, the heating rate can tell us what parameters we need to use in the next step.
For example, if the rate of rise ramps up and then starts to flatten out to form a spike, we know that the roast is about to start slowing down. Then, you can adjust the temperature drop rate according to your own roasting purpose to adjust the roasting.
Likewise, if the ROR drops and starts to level off, that means the roast is about to start speeding up. We pay special attention to the formation of these temperature peaks and valleys, especially if our roasters are slow to respond to changes in thermal energy input or airflow.
We can also influence the chemical reactions in the roasting process by manipulating the rate of rise. For example, combining an increase in bean temperature with a gradual decrease in the rate of the ramp increases the roasting time of coffee in the temperature range where Maillard reactions and caramelization occur.
It’s hard to know when to make more than proactive changes if we don’t know what the rate of warming is. We often make mistakes in the baking process because we miss important moments when adjustments need to be made.
Environment or air temperature refers to the measured temperature of the environment inside the roaster drum. It is closely related to the convective thermal energy available to us.
At the beginning of roasting, there will be a large difference between the environment temperature and the coffee bean temperature. This is because the coffee beans are at room temperature. During the entire roasting process, the environment temperature and coffee bean temperature should gradually approach.
As for bean temperature, it is difficult to discuss its absolute value because the temperature probe will vary due to various factors. However, it can still provide a lot of useful information. For example, when we see a sudden drop in environment temperature, there is a problem with the roast, as it indicates a loss of convective heat energy during the roast.
This is an important metric for baristas, as it can also tell us if aggressive adjustments are required when using controlled variable inputs. You should know that when the environment temperature changes greatly, it may tell us that the environment temperature change is affected by the input of fuel or heat energy.
Rate of Environmental Change
The environment rate of change is the environment temperature related to the effect of the heating rate on the coffee bean temperature: it measures how the environment temperature is changing. A positive environment rate of change means that the heat energy in the roaster drum is increasing regardless of the environment temperature. This may be a more useful indicator than environmental temperature.
But the key is how quickly that changes. To a barista, the numbers themselves are not important, but the rate of change is.
One practical way baristas can use this data is with respect to the first crack. Most baristas intend to slow down the roast significantly at this point, but it is easy to over-roast. We need to keep this number positive until the first burst. A positive environmental change rate means that even if the temperature profile flattens, there is enough energy in the tumbler to continue developing the coffee beans. Conversely, if the rate of environmental change becomes negative, heat is lost from the drum. The bean temperature may continue to rise, but this is because the conductive heat from the drum and mixing blades is doing most of the work, thus causing uneven bean development.
Of course, it is also important to know our roaster: depending on its capacity, the material of construction, and the technology employed, the time required to affect the rate of environmental change will vary. If we don’t know how the roaster responds to heat and air, we can’t control what’s going on inside the machine.
Intake Air Temperature
This data allows baristas to understand how air reacts to convective heat as it enters the roaster, allowing us to predict what will happen next. This information is important because it can tell us at what point we need to add heat to the coffee bean, or how much the temperature drops from the point where the coffee is added heat to the lowest temperature reheat point. If the inlet air temperature is low, the roaster must first be warmed up to prevent the possibility of destructive drying of the coffee beans.
Exhaust Air Temperature
As with the inlet temperature, it is useful to know the exhaust temperature of the roaster. For the barista, they are great indicators of what is going on during the roast, sometimes about the coffee of course, sometimes just about the machine itself. If the exhaust temperature of the roaster is too high, it may catch fire.
Coffee Bean Weight Loss
Different coffee bean densities and different moisture levels inside the beans will mean subtle but noticeable differences in weight loss between different coffee beans.
If the weight loss of coffee beans is too much, we need to shorten the roasting time or reduce the temperature of the coffee beans. This is critical to maintaining coffee flavor consistency and operating margins. Because it’s a direct cost to the business. From a numbers standpoint, if we manage the profit and loss numbers for a roaster fairly strictly, then knowing the average weight loss based on a year’s worth of inventory is very important for figuring out the cost.
If we were to roast a million pounds of coffee beans a year, and when we thought we were only losing 15% moisture, but actually lost 19%, we lost 4% of the total coffee weight in a year, which is It’s still a lot of money.
Time Scale of Development
This is the time it takes from the start of the first crack to the end of the roast, as a percentage of the total roast time. But why is the time after the first crack so important? From the moment those beans pop, they’re incredibly volatile, and the beans absorb heat faster after the first crack than at any other point in the roast.
After the first crack, the organic acids burn off quickly, while bitter compounds begin to emerge. This means that the balance of flavors in the coffee shifts from predominantly sour to predominantly sweet after the first crack. Unless you’re doing a sample roast, you’ll probably want at least some of these three main flavors. Knowing the time scale of development will help us stay within the bounds of the right roast.
Only consider the development time scale as part of the final roast time. For example, if we roast a large batch of espresso. In hot weather, it typically takes more than 14 minutes to roast and can take as much as 1 minute and 35 seconds to develop. However, if roasting in extremely cold weather, the roasting time needs to be extended to 16 minutes, and if we still use the development time of 1 minute and 35 seconds, then the proportion of the total roasting time drops. In this case, even if the development time is the same, the coffee beans may appear to be underdeveloped.
The ratio of final temperature and development time we target will provide a very limited reference for the end roast, which can help us maintain a balanced coffee flavor at all times.
Even if there are fluctuations caused by factors beyond our control, data can provide us with strong support for maintaining consistency. Environmental changes can have an effect on roasting during different seasons. The more data you have about previous successful batches, the easier the replication process will be. Without relevant knowledge such as development time ratios, it will be difficult to consistently replicate a roasting plan that maximizes a coffee’s flavor potential,
Bean and environment temperature and rate of change curves are the primary data that can be used to guide each batch in a specific roasting plan. The intake air temperature and exhaust air temperature provide more reference details for the conditions inside the machine. Measuring weight loss can help us track roast consistency and cost. Developing time scales, along with time and temperature, will help remind us when the roast is done.
Proactive and more consistent roasting is possible using data analytics. We can also use it to predict how to improve the roasting plan and troubleshoot any issues that arise.