When it comes to roasting coffee, we roasters have two main jobs. Firstly, when each new coffee arrives, we need to figure out how to roast it. We look at a whole range of factors including the green (or unroasted) coffee’s density, moisture content, screen size, how it’s processed and how we’ve roasted similar coffees previously. Then, over the first few roasts, we’ll gradually tweak our profile until we’ve come up with a roast we’re really happy with that we’ll designate as our reference.
Our second job then is to keep every subsequent roast tasting as close as possible to this ideal or reference, which brings us to the wonders of QC, or quality control
DATA
In order to keep our roasts tasting as consistent as possible, we need data. We roast on a very lovely Loring S35 Kestrel (which is about as state of the art as you can get) which has temperature probes that track the temperature of both the beans and the environment inside the roaster. During a roast, this data pushes through to our roasting software (we use Cropster) which tracks these values on a graph in real time, and allows us to make adjustments as we roast.
Cropster also allows us to set up automatic checks for just about anything, and will flag up a roast if it scores outside the range we specify. For example, if we have a reference roast that takes a total of 10:00 minutes and have allowed for a range of +/- 10 seconds, when a roast takes 10:11, it will be flagged up on our dashboard. There are a few factors we know have the potential to really impact flavour, so with alerts set up for these, it becomes easy to see when these targets are missed and to set the roasts aside for further tasting.
COLOUR
Another important indicator of flavour comes down to the colour of the coffee. Just as we know a super dark coffee will likely taste ashy or bitter, more subtle differences will also often have a corresponding difference in colour. In the roastery we have a small device called a colour meter which we use to measure the colour of both the outside of the roasted coffee beans (for an external reading) and ground coffee (for an internal reading). We colour track every single batch we roast, and again, after inputting this data into Cropster, any roasts that score outside of our ‘acceptable range’ are then flagged up.
CUP CUP CUP!
So, in contrast to these more data-based analyses, our final and perhaps most important check is a sensory one. At the end of the day, it all depends on how the coffee tastes!
At PLOT we have a weekly production cupping where we taste every filter and unique espresso we’ve roasted from the week before. We compare the coffees to a reference cup (from the previous week’s roasts), and assess the acidity, sweetness and bitterness of each coffee on the table. This is also a chance for us to flag up anything else we notice, for example if we’ve found any defects, or if any signs of age are beginning to show.
WHY QC?
So at the end of the day, you might be asking why we put so much time into our quality control. The short answer is for consistency, but surely the follow up question is then why is consistency so important?
For any of us who have worked as baristas, we know how tricky and changeable coffee can. For cafes running with multiple espressos, pour-overs and batch brews, there can be upwards of five coffees to dial in, with recipes that change based not only on the coffee, but on how rested it is, how cold the morning’s been, where you are in service and even on whether it’s raining outside.
On the opposite end of the spectrum, the number of variables farmers and exporters have to navigate (from weather, to picking, to processing, to transport) is mind blowing, each of which has the potential to affect the coffee in your cup. So while we of course have challenges of our own to tackle, our ultimate goal is to have the coffee in your cup tasting its best. When we keep our roasts as near to identical as possible, we’re aiming to remove one small variable in a coffee’s very convoluted journey, and hopefully brings you a tiny bit closer to having a banging brew every single time.