Roasting at home

by Marijn Dokter

Data when roasting coffee

Roasting coffee is all about two key data: temperature and time. Whereas the latter is simply measured from the start of the roast, the former is obtained through temperature probes. These probes measure temperature in certain places. Most of the time there is a probe in the bean mass, and a probe outside of the bean mass, either in the exhaust or above the bean mass. The data on every roaster will differ a bit because of probe placement. For instance at Shokunin (a Giesen W6) we have a first crack temperature of 190°C, whereas my home roaster (a Quest M3S) has a first crack temperature of 203°C. This data is essential if you want to replicate roasts, which is important in a production environment like a roastery. If you’re roasting at home, data is less essential, but can still help you a lot to get better roasts. 

Quick sidenote here: temperatures depend on probe readings and differ for every roaster. The temperatures mentioned in this article are just to give an impression.

Stages of coffee roasting

Before coffee is roasted, it is green and very hard and it smells somewhat dusty. As the coffee is roasted it transitions from green to yellow and eventually to brown. These colour changes are milestones during roasting and can help guide you influence the flavour of the eventual coffee. The first phase during roasting is the drying phase (also called yellowing). This phase lasts until the coffee turns yellow, generally around 150°C.

When the drying phase ends, the maillard phase (also known as browning) begins. In this phase, Maillard reactions start to occur, giving the coffee its brown colour and constantly changing the coffee’s flavour. This phase ends when first crack starts, which is typically around 200°C. First crack is usually easily recognizable: the coffee “cracks” and it makes a sound similar to popcorn popping. The phase that happens after the beginning of first crack is the development time (or post-crack phase). 

Effects of roast time on taste

Before roasting coffee cannot be consumed as we know coffee, so the roasting process has big impact on the flavour of coffee. We usually say a coffee needs to be developed before it can be brewed. If you pull the coffee out shortly after first crack has started, there will be a lot of characteristics left that the coffee originally has. The coffee will have a lot of acidity and a lighter body and mouthfeel. If the coffee is developed more, many of the lighter aroma and acidity compounds will slowly disappear. Sugars are caramelized and therefore the coffee gets less acidic and sweet and more bitter. At Shokunin we roast quite light, because we like to showcase the flavours that different coffees from different farmers have. We try to keep as much flavour intact as we can while still balancing all those flavours out and not imparting any recognizable bitter flavours with the roasting.

Most of the differences in flavour and roast level happen after first crack, during the development phase. But what about the drying phase and maillard phase? They also influence the taste of the coffee. If you push the coffee through these coffees quickly, the coffee will be more lively and “funky”. If you take it a bit slower, the coffee will be a bit more mellow. This is something we play around with when making roast profiles, based on every coffee’s unique flavour profile.

Roasting at Shokunin

At Shokunin we roast fairly light, but we try to properly develop the coffee for espresso and filter, an omniroast. Most of our coffees get to first crack in a little over 8 minutes. We go into first crack at 190°C and most of our coffees are dropped around 195°C to 196°C. Important to note is that even a difference of 0.2°C already gives a noticeable taste difference. This is why we have strict guidelines for our end results to determine if we can sell a batch of roasted coffee or not. We use a fixed airflow during the roast, which depends a bit on the coffee, for some it’s a bit higher than for other coffees. Our drumspeed and batch size, which are always related to each other, are also fixed so that our coffees’ flavours are as consistent as possible.

Roasting at home

Roasting at home is totally different from roasting in a production environment. The best part about home roasting is that there is only one person to please and that is yourself! When home roasting it is not that important to exactly replicate your roasts. We have experience with two different homeroasters, the Gene Cafe CBR-101 and the Quest M3S. For both machines we’ll give you some tips to get the best out of them!

The Gene Cafe is a little limited in its control. It doesn’t have a lot of power, but you can still get a good cup out of it! To get the most out of the Gene it should be preheated to the maximum temperature. Once it reaches the maximum temperature (250°C) you should stop the roaster, load it as fast as possible with 200 grams of coffee and put the chamber back in and turn the heat to max again. The reason for this is that this roaster heats the coffee somewhat slowly, so you need to retain as much energy as possible for adequate development. The only temperature reading the Gene gives you is the air temperature, so you need to pay attention to the beans. The most important thing with the Gene is to use your sensory skills. Depending on the color of the beans and the smell of the beans you have to make the decision of when to end the roast and drop your coffee. To extend the development time you can drop the temperature a bit after first crack occurs.

The second home roaster we have some experience with is the Quest M3S. The Quest is a small drum roaster working on electricity. Compared to a roaster on gas it’s a bit less nimble, but there is no hassle using gas or propane stoves or bottles. A huge advantage of the Quest M3S is the possibility to data log your roasts using probes. With these probes you can track your roasts in data logging software like Cropster or Artisan. This makes it easier to replicate roasts, or to adjust your roast profiles. With the Quest we mostly use maximum airflow throughout the whole roast since the fan is not very strong. The Quest allows for batch sizes from anywhere between 150 grams to 250 grams for proper development and probe readings. Charge temperature is anywhere from 180-200°C, depending on the charge weight. We try to hit the coffee with a lot of heat from the start, until the coffee turns yellow. Then we gradually lower the heat until first crack. With the Quest you need to plan ahead a bit; its electrical elements take a while for an adjustment to kick in. This is a disadvantage of an electrical roaster compared to a gas roaster. However, if you plan your roast well and get good results, replication is easier and you’ll get some delicious brews.

Views on roasting before and after Shokunin

Before I joined Shokunin I was a bit sceptical about omniroasts, mostly because the ones I had I did not like very much. They were either too sour for espresso or a bit roasty for filter coffee. Doing almost exclusively omniroasts at Shokunin is quite a change for me! Before I joined Shokunin I worked at the Stielman coffee bar, which used Shokunin coffee a lot. At this point I was a bit surprised with the coffee, because it worked for filter and for espresso. At Shokunin I learned that to do omniroasts well the body of the roasted coffee is really important. It needs to hold up in an espresso, but it should not be overwhelming for a filter coffee. Using this balance, both the filter coffee and espresso turn out nice. The effect of the omniroasts on our coffee is that our espressos are a bit more punchy whereas our filter coffees are a bit more soothing and smooth.