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There’s a lot out there about the specific temperatures at which beans reach particular stages in the roasting process, and which chemical processes are taking place to produce which flavors. The temperature charts make interesting reading, and it’s nice to know what’s happening to your beans, but almost to a man (or woman), home coffee roasting experimenters agree on one thing – trust your nose and your eyes more than your thermometer. Of course, before you can trust your senses, they have to be developed, but these guidelines will give you a general feel for how to judge the stages for home coffee roasting.
Green coffee beans are generally stored at room temperature. They have a moisture content of about 15%. Roasting heats the beans to temperatures of around 450 degrees, forcing the rapid expansion and evaporation of that moisture content. At the same time, the heat cooks the proteins and sugars that are present in the bean, which deepens and broadens the characteristic flavors.
Stage I – Heating the Beans
The coffee beans will heat up without noticeable changes until they reach about 212 degrees. At this point, the color will begin to change from greenish to yellowish, and the beans will start to release steam. No matter what type of bean you’re roasting, you’ll smell something close to the aroma of straw.
Stage II – Cinnamon Roast
Between 212 and 240 degrees, the beans will gradually darken to a rich cinnamon color and begin to dry. This Cinnamon Roast is pretty common in less expensive supermarket coffees on the East Coast. The beans haven’t reached first crack yet, and the flavors have barely begun to develop. The flavor of coffee at this roast is lightly acidic, with a light body.
Stage III – First Crack
From 250 to about 300 degrees, the coffee beans are drying out and expanding. At about 350 degrees, the continued heating will cause an audible crack as steam breaks through the outer skin of the coffee bean at the existing steam. You’ll usually see a lot of chaff floating around at this point as the remains of the outer husk are separated from the bean. The coffee bean is a light brown color at this point, and stopping the roasting process now will give you a “Light City Roast”, or “American Roast” coffee, with rich flavor that still takes more from its origin than from the roasting process. This is the ideal roast for making espresso, despite the widespread belief that darker roasts make more flavorful coffee.
Stage IV – City Roast
Between 350 and 400 degrees in the coffee roasting process, the sugars inside the coffee bean start to melt and carmelize. This is the point where you really have to start trusting your nose and your eyes. Generally, you’d stop the roasting at about 425 degrees for a full City Roast – and cool it down fast. At this point, you’ll find that there’s still a lot of the specific flavor notes from the origin left, but the characteristic flavors of carmelization are beginning to make their presence known. The acid content of the coffee is beginning to mellow to a smooth, sweet flavor.
Stage V – Second Crack
Between 425 and 435 degrees, depending on the variety of the bean, the coffee will reach the “second crack”. This is the second audible cue, and it sounds a great deal like popcorn popping. During this stage, the flavor of the beans changes rapidly. Many roasters break this stage down into several stages, from the beginning of second crack (a full city roast) through rolling second crack, when the majority of the beans are popping (a medium French roast) to diminishing second crack, when most of the beans have cracked and are starting to burn (dark Italian or Spanish roast).
By the second crack, the beans are beginning to gleam with oil that is released as the sugars carmelize. The flavor of origin decreases until it is not in evidence at all. The darkest roasts of all have a bitter, burnt flavor to them that is actually favored in some areas of Italy, Spain and Cuba.