The Art and Science of Roasting Part 2

Here is part two of my series on roasting coffee. Again, my source material comes courtesy of Blue Bottle.



The roaster has started his machine. The green beans are in the drum. At this point the roaster(person) is waiting for the roaster(machine) temperature to bottom out. ONce this happens the first stage of roasting is complete. 

Beans are typically held in a warehouse at a certain temperature. According to Blue Bottle:

The thermal mass of the coffee brings the much greater mass of the roaster down from about 380F to its lowest point - usually 180F to 190F depending on the weather and the batch size. The amount of time it takes to get to the lowest point tells you how much energy you’ll need to put back into the coffee to get it through the roast.

Science is truly at play, because you have to deal with weather, temperature, mass. You have a lot of estimating to do to get those beans to where you want them roast-wise. Because you are dealing with issues of taste and aroma, this is also art. From this science, you are creating something which will please the mouth, eyes and nose. 

Once these beans have bottomed out temperature wise, it will begin to rise, and the roaster’s mission at that point is to prevent the temperature from climbing up too fast. You want a steady climb. Too quick a rise, and coffee dries too quickly. 

The steady rise in the temperature goes until there is the first cracking. The first crack is a chemical reaction , similar to the first pop of popcorn. This popping means there is now an increase in the size of the beans, and a decrease in the density of the bean. Coffee is now beginning to be drinkable with this first crack. 

There is a balance at play now. Moisture is leaving the coffee, but you don’t want it too dry. The coffee is getting browner as the temperature rises. The roaster has some decisions to make. He knows there is a certain roast he is going for. Whether it is a lighter roast, or a darker roast, he has to tinker with the machine and watch the time and temperature to achieve the roast and taste he wants in a coffee. 

Blue Bottle explains it this way:

The short period of time before, during and after first crack - approximately 120 seconds total - is when we are most consumed with changes in roasting variables. We want the temperature of the coffee to rise, but we want to manage the rate very carefully. If the temperature rises too quickly, momentum will carry the coffee past where we want it to be.

It’s a challenge. You need to work towards a goal, and if you fail, you have wasted beans, time and money. That is a lot to juggle.

Next, I will discuss what happens after first crack.

Charlie