Behind its aesthetic appeal, the IKAWA home roaster is a smart piece of engineering. Paired with the App, you have everything you need to apply heat to green coffee beans precisely, in a controlled and repeatable way. Pressing the start button begins a process of complimenting systems that make sure the coffee is roasted in the way that you have chosen.
When you press the start button, the fan motor, the only moving component of the machine, will begin rotating. The fan does many things, but firstly, it draws room temperature air into the roaster. This air is then moved upwards into the roasting chamber, past an electric heating element. As the air is moving past the heat source, the temperature is measured by a precise temperature sensor (this is the temperature you will see on your App, referred to as the “inlet” temperature).
The air, now hot, is blown into the roasting chamber and is doing several things at once.
- It is transferring heat to the beans as it passes around the beans
- It is moving the beans, allowing evenly distributed heat transfer
- The hot air is entering the roasting chamber in such a way that creates a cyclone effect - important to ensure evenness, prevent smoke build-up, and to neatly collect the chaff as it separates during the roasting process.
Throughout the roast, electronics are simultaneously receiving data from the temperature sensor and using that information to make adjustments to the heat source according to the roast recipe that has been sent to the roaster. This same process is used to ensure the airflow , the speed of rotation within the fan motor, is accurate. The inner workings of your IKAWA Home roaster continue these tiny cycles of measurement and adjustments until the roast recipe has finished. At the end of the roast recipe, the fan kicks up a gear to allow fast cooling of the beans before being ready to eject the freshly roasted coffee.
Roasting coffee, simply put, is applying heat to green coffee beans.
This application of heat is a catalyst for chemical reactions to take place in the beans, which changes the physical and chemical qualities of the coffee. Besides processing, variety etc, heat application and how and when the heat is applied during the duration of the roast recipe has the biggest effect on the resulting flavour of the roasted coffee.
The IKAWA Home roaster seeks to maximise the impact of convection heat transfer, whilst minimising the impact of radiant and conduction heat transfer. This is to allow as much control over the roast as possible. Let’s take a look at this.
While there are elements of radiant and conduction heat transfer in the Ikawa Home roaster, these methods of heat transfer are minimised by using aluminium and other materials that do not retain heat energy. The main method of heat transfer in the Ikawa Home roaster is convection.
Through convection heat transfer, the Ikawa Home roaster heats the air that is blown into the roasting chamber, heating the coffee beans. The air might need to be heated to a very high temperature or kept at a low temperature, based on the coffee that is being roasted. Low density, low elevation grown coffee generally needs lower temperatures to be properly roasted, while high density, high elevation grown coffee tends to need higher temperatures and sometimes, a longer roast recipe.
The heat in air is much more controllable and fit for our purpose of roasting small batches of coffee precisely according to our programmed roasting recipe.
The IKAWA Home Roaster is measuring the temperature of the air immediately after it has passed through the heat source, using the internal PT1000 temperature sensor. We call this measurement the “inlet” temperature because it’s the temperature of the air input to the beans.
In most professional level roasting machines, the temperature is measured in a position that better represents the actual temperature of coffee beans (often called the “bean” temperature). To do this, these machines need to use a more durable and therefore less precise (increased resistance for those who know!) temperature measurement device - sometimes called a probe. This type of probe would not suit IKAWA Home in its current form because of the importance our machine places on the temperature measurement and the role it plays in how we control each roast - requiring precision and fast-reaction. This makes IKAWA home recipes look very different to the average roast profile you will find on google or books written by various Coffee Professionals.
These two different approaches to measuring the temperature - ‘inlet’ and ‘bean’- are aimed at the same thing: to control and roast a coffee really well.
Of course, these two measurements will correspond to one another. In the same way slamming the brakes on a car would eventually lead to the car stopping, drastically decreasing the temperature of heat applied will pause the coffee from roasting further.
For the purpose of changing a roast recipe, we can use the inlet temperature to control the acceleration or deceleration of the heat input and we can use distinct (and visible) stages of a roast to understand ‘how fast the coffee is travelling’.
Whether you are using Guided Edit or Advanced Graph Editor mode on the iOS App, or the Android App, the IKAWA Home Roaster still works the same way- The app simply provides the roadmap for the roaster to follow via the roast recipe. If you are curious about the technical aspects of the IKAWA Home Roaster, you can find more information here and learn a bit more about IKAWA Home’s origin here