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By pigwhisperer, December 1, 2009

It’s been a long road for our coffee beans. Now they head into the final phase of their lives: the roasting process. Like cooking, coffee roasting is an art and a science. Here I am beside our brand new “little red roaster” from Ambex. Terry Davis, master roaster and Ambex owner, visited the farm to give us a few roasting lessons. Here’s what we learned.

The Science
Roasting is applying heat to a dry coffee bean in order to alter its chemical composition. Dry or “green” coffee beans drop into the roasting machine, which is basically a drum with heat flowing underneath it. Air also flows through the roaster. Many master coffee roasters say it’s not heat but air flow—which moves heat through the drum and around the beans—that cooks the coffee. After a few minutes in the roaster, green coffee beans become yellow. Beans begin to smell like popcorn or bread baking. The coffee is going through an endothermic reaction: beans are sucking in heat, and this heat is changing them. Early in the roasting process, you’ll hear a popping sound. This is called the “first crack.” No worries, the beans aren’t going crazy; they won’t need Xanex. They are expanding in size, losing water, and turning light brown. Pyrolysis is happening. (Pyrolysis should happen any time you cook anything.) This is a Greek word that means that elements (CO2, water, etc) are being released, good flavors are formed, and bitter compounds and toxins are destroyed. Also, sugars in the coffee beans begin to caramelize, which means the beans get sweeter.

Towards the end of a roast, beans also get darker. Another crack happens, and this time the beans become exothermic. Each bean is now releasing energy (heat) instead of sucking it up. Explosions do this. Apparently, so does coffee as it roasts. When you hear the second crack (and you can hear the loud popping noise even while the roaster is running) it means the chemical process is entering an important yet precarious stage. Beans start to release oils, but they also start to carbonize. If you’re not careful, you’ll have the perfect ingredients (oils + heat + organic matter) for a drum fire. This is why a good roaster never leaves her machine while it’s running. Does this mean that leaving beans in the drum past the second crack is bad? How long should coffee roast? This is where science ends and art begins.

The Art
How much heat should you give your beans? For how long? And how much air flow should the drum have? Like any art, roasting has no fixed rules. (Other than staying beside your roaster while it runs, of course!) Roasting relies on the senses. You have to smell the beans, look at their color, listen for the first and second cracks, and then taste each batch of coffee when it’s done. Every coffee is unique. Beans from higher altitudes are generally denser. Lower attitude beans are softer. Older beans are often drier than younger ones. Some beans have a lot of chaff, or bits of papery skin on them. All of these characteristics affect the roast. Even beans from the same farm but from different harvest years can vary in flavor. Bags from the very same harvest can also vary subtly. Every crop of beans has a roast profile (or recipe) that brings out its best flavor. It’s up to the roaster to find that optimum roast and recreate it. And a roast can’t just be good once. The profile, or recipe, must have continuity for that particular batch of coffee—you have to be able to recreate your best batches again and again. A lot of roasting depends on taking really detailed notes while you roast, and then tasting the coffee after it’s been roasted.

What does coffee tasting involve? What flavors should a good roaster look for? I’ll cover this in my next post. This post is getting long; in roaster’s terms, we’ve reached the second crack. So I’ll stop this batch while it’s still palatable.

Thanks for reading!
Frances