Amazingly, to create all the chemical and physical changes to make green coffee brown, all we have to do is add heat and time. The IKAWA Home Roaster has another element of airflow, through the fan speed controls. The art of roasting is in how and when heat is applied, as well as controlling the airflow through the roaster i.e. the speed that the beans move around in the roaster. With careful monitoring of how quickly or slowly the coffee is roasting, we can learn to tease out the flavours we love in coffee and avoid those we don’t like as much.
Luckily for us, we can monitor the visibly different colour stages of the beans through the glass lid of the IKAWA Home roaster. The colour changes occurring during the roast gives us a really good idea of what is happening to the coffee. Each IKAWA Home roast recipe begins with loading a preset roast recipe onto the IKAWA Home Roaster via Bluetooth.
After the recipe has been sent to the roaster, the green beans are loaded into the roasting chamber through the twisting of the doser, before hitting the illuminated ‘Go’ button. The temperature of the green beans at this stage is low (room temperature). It’s therefore really important we inject enough heat at the beginning of the roast to get the roasting process moving at a decent rate.
Our roast recipes differ the most from roasting profiles you may see elsewhere on specialty coffee sites, or forums. This is to do with the way the temperature is measured, using the inlet temperature measured by the PT1000 sensor. With the IKAWA Home, we are beginning to roast green coffee at room temperature and there is no preheating necessary on the IKAWA Home. We need to begin the roast recipe with a considerable injection of heat so we can quickly move our raw beans to its first key stage of roasting, yellowing. Generally speaking, that means that we want to see the green beans begin to turn yellow within the first 3 minutes of the roast recipe.
TIME AND TEMPERATURE
Changing the inlet temperature on the roast recipe represents the most important way we can change our roasts because heat application has, by far, the largest impact on the different roasting stages.
On the IKAWA Home App in Graph Editor on iOS or in the Android App, you will see this as the red line plotted across temperature and time. Each recipe in Graph Editor will have up to six points that we can add, remove, and change, to shape the roast recipes to best suit the needs. These points can be changed by as little as one degree and one second, giving us an almost infinite range to work with. The points along the red line on the graph, simply have to be selected by clicking on them and then dragging them to the new temperature point that you would like.
Exceptions are that we cannot apply temperatures above 290˚C (or 554˚F) to maintain safety (and to be honest, because we wouldn’t want to anyway!) and we cannot roast longer than 12 minutes (for similar reasons).
As a general rule of thumb, dense, high elevation grown coffees need slightly higher temperatures than a low density, low elevation grown coffee would require to reach the same roast colour and development. You can see in some of the IKAWA Guided edit recipes viewed in Graph Editor, that to achieve a light roast colour, that the temperature seems to level out, or decrease through the end of the roast recipe after first crack is achieved. Inversely, you may also see that for a dark roast colour, the temperatures tend to be higher after first crack, to ensure a true dark roast (see the examples below). All of this depends on the green coffee though, as well as your local roasting conditions (think elevation, humidity, season, barometric pressure).
This is controlled by the black line that is visible in Graph Editor on iOS or in the Android App. The fan speed is expressed as a percentage between 60% - 100%, and can be changed with up to three points, four if we include the cooling phase. This line represents the speed of the fan motor (the RPM). The fan is necessary to move heated air into the roasting chamber. This hot air that is forced into the roasting chamber will serve two purposes; rotate the beans, and create the patented cyclone system that draws the chaff to the collection jar and dissipates smoke during roasting.
Airflow can dramatically change the process of transferring heat to our coffee beans, and counterintuitively, a lower fan speed tends to create a much darker roast, and a higher fan speed generally creates a lighter roast colour.
Fundamentally, the airflow needs to be moving the coffee beans freely in order to provide even heat distribution and to avoid over-roasting the bottom (or under-roasting the top) of the coffee. If you are creating your own roast recipe, be wary of reducing the fan speed by too much as this can result in burned beans and possibly smoke!
How much airflow it takes to achieve this can vary depending on how dense and fresh the green coffee is. Density and freshness are important to bear in mind, if for example you notice your beans not moving freely enough, particularly at the early stages of a roast when the beans have not dried out yet and are heavier than they would be at the end of the roasting process. Additionally, using your roaster at elevation can create variance in the airflow of your roaster, as air at elevation is thinner, drier, and can affect the way heat is transferred to your coffee. Generally, at an elevation of 1200 MASL, a higher fan speed will be needed.
If you are curious about getting started with the Graph Editor to further experiment with coffee and roasting with your IKAWA Home, there is not necessarily a right or wrong way to begin. We recommend focusing on the temperature controls as you get started.
As you become more comfortable with using Graph Editor, experimenting with airflow as a way to change the key stages of a roast can be really interesting. We suggest being empirical about any adjustments that you make to your Graph Editor recipes: make one adjustment to airflow/fan speed or Time and Temperature at a time and take notes on what worked best for you.
The IKAWA Home app is free to download and use. Graph Editor is available via a subscription within each roast recipe,after download. This subscription is managed and attached to your AppleID. We highly recommend downloading the app prior to purchase to have a look around at the different coffees available to add to your coffee library and all of the roast recipes that are nested in those coffees. You can read more about our App in this previous blog.