Roasting Coffee

Now that we've settled into our new home and are roasting all of our coffee, you've probably seen somebody standing at the back of the shop watching a large machine, occasionally moving a lever or taking a note. What's going on is coffee roasting.

Coffee starts out as bright red berries on coffee trees and get to us in the form of small green beans. Our photo albums show the intricate process by which coffee makes that transformation. While it can be difficult to tell a coffee from Papua New Guinea apart from a coffee from Costa Rica by looking at the green beans, different coffees behave quite differently in the roaster due to variations in bean size, density, and moisture content. Similarly, due to various methods of processing, soil conditions, and weather patterns where the coffee is grown, different coffees have different flavors and require different styles of roast to make the most of them.

In order to determine the best way to roast a particular coffee, we roast a small batch. This is done on our roaster, a Diedrich IR-12 Deluxe made in Sandpoint, Idaho. This machine only roasts the coffee and does no grinding. We can roast anywhere from just a handful of beans up to thirty pounds at a time, but to determine how the coffee should be roasted we use about three pounds of green coffee.

While roasting this test batch, we record the temperature of the beans every thirty seconds as well as how air is flowing through the roaster. This is called the roast profile and allows us to easily duplicate the roast. As the coffee is roasted, several changes can be observed. First, when the coffee reaches about 300°F, it changes color from green to a bright, straw colored yellow. This marks when chemical changes in the beans start happening. By 330°F, the coffee has changed to a very light brown color. The coffee is still too light to taste good. The color becomes a little darker as it approaches 380°F when popping sounds can be heard. At this time, water in the beans is evaporating and breaking some of the cell walls in the beans. This is called the first crack or the first pop. The coffee beans then begin to increase in volume and take on darker hues. This is when we start to pull samples. The coffee is still too light, but to determine how best to roast the coffee, we want a range of samples from too light to too dark. For every sample we record the time and the temperature. At about 430°F, the second crack, much louder than the first, starts. At this point the coffee changes very rapidly. The beans have by this time roughly doubled in volume. By about 460°F, the coffee takes on a color similar to that of dark chocolate and if let to go on to about 475°F the beans become black and are almost certainly too dark. All of this (from the start of the roasting process) happens in less than 20 minutes.

Once we've pulled several samples from the test batch, we let them sit for at least a few hours and possibly overnight to allow the flavor to develop more fully. Then we taste each sample and decide which one is the best. Sometimes we get a sample that's just right on the first try. Sometimes we suspect the right roast is between two samples. Sometimes we find the right degree of roast but need to change how long we roast the coffee in some range of temperatures. In those cases, we roast another test batch, pull samples from a smaller range with less time between samples and taste it again. Eventually, we have what we suspect is the perfect roast for that coffee. We then go back to our record of the roast and using that as a guide along with the portion of our ideal sample to use for color matching, try to reproduce that coffee by matching the profile and color. Once that is done, we determine the percent weight loss as another indicator to match on future batches and taste the coffee again to make certain it still tastes right.

Only after all of that has been done does the coffee become available for sale. We continue to taste the coffee to ensure that each batch is as perfect as the first. We also occasionally repeat the test roasting process, adjusting the profile in search of increasingly tastier ways to roast the coffee. By monitoring the time and temperature throughout the roasting process as well as comparing the appearance of the bean and the weight loss due to roasting, and by constantly tasting the coffee, we can maintain a high level of control over the quality and consistency of our coffee. The ability to roast small batches of coffee allows us to roast just what we need, just when we need it, guaranteeing that the coffee is always as fresh as possible.

Our roaster loves to talk about coffee and coffee roasting. If you have any questions, please do not hesitate to ask.