What's Happening When You Roast?

By now you’ve probably already tried roasting some coffee. Hopefully you’ve got a roaster that really lets you see the beans roasting. They start a pale green, then get to a khaki color.  As the remaining moisture leaves the beans, it smells kind of like hay. They gradually turn tan, sable, and then brown.

You heard hear a dull popping sound. This is First Crack. It’s the bean changing shape, expanding.

Depending on factors which we’ll get to later on, you may have a period of quiet, or your beans may have gone straight into Second Crack. Second Crack is a sharper sound. Its the sugars beginning to caramelize. Up to this point, your beans have probably not been that smokey. If you keep going you’ll get some real smoke.  The darker you go the more critical timing becomes. Things go slowly at first, then pick up speed.

Under roasted beans will have a cereal or grassy taste to them. Over roasted beans will taste burnt and lack any real flavor. Between these two ends is your target. How you get there, and how fast, makes all the difference.

The speed at which you roast will affect the outcome. Generally a very fast roast will produce brighter tasting coffee. Extend the time way out and you gain body at the cost of that brightness. You can accentuate or mute what’s already inherent in a coffee by the speed of the roast. If a coffee is all about body in the first place, you may want to do a fast roast to enhance it’s brightness. If you roast a Kenya coffee, for example, that’s just too much sunshine in a cup, extend that roast next time to mute the acidity and gain a little body.

The specific thing that’s happening in second crack are the sugars caramelizing. This is just like Cracker Jacks or creme brûlée. The sugars are cooking and browning  replacing sweetness with the taste of browning sugar and eventually the taste of charcoal.

If you think about it… a lighter roasted coffee is actually more sweet than a darker roasted coffee. The lighter a coffee is roasted the more varietal nature remains there. The darker the roast the more the nature of the coffee gets replaced with the process of roasting. You taste the process, not the coffee. It’s a matter of balancing what you like. Also a good reason to play with blending coffee later on.

Speed of roast is why sometime people prefer small fast air roasters like a FreshRoast over a slower drum style roaster like a Gene Cafe. But the beans you choose will also be a factor too.

Can you get the best of both worlds? Fast AND slow?  Yes. Simple trick- reach first crack then drop the temperature just a bit, to slow the progress of the roast. This will extend the period of time between First and Second. You will also be roasting more uniformly through the center of the beans.

Let’s say you're roasting a bowling ball with a flamethrower. The outside is going to get all that heat energy first, followed by the inside. You want to roast your bowling ball fairly quickly, so it roasts rather than bakes, but you don’t want the inside to be different (brighter) than the outside. In the extreme, scorched and raw.  So how fast you roast makes a difference. And, baked bowling ball, like coffee, is flat tasting, with no life to it.  If your coffee is plenty brown, but flat and you’re not sure you reached second crack, maybe you baked it, try roasting faster.

Bowling ball’s are easy. That’s why a lot of people like to roast Peaberry beans. They’re round and uniform. But most coffees are a hemisphere like a cookie so its trickier.  Cookies are fat in the middle and thin at the edges. You’ve seen the thin edges of cookies get burnt. The same thing happens with coffee.  This is an argument for creeping up on a roast, not too much heat at first, so the cookie (coffee ) middle can match the thinner edges. You may want to start with low heat, drive off the remaining moisture, then ramp the heat up over time.

Or, you may want to set your coffee roaster on flamethrower setting right away and go for it because you like getting a range of tastes out of that single bean. Totally up to you. Keep in mind that the volume of coffee you roast will make a difference in how fast you roast too. A larger mass of beans will take longer than a smaller mass.

Specific beans each have a nature. This is just an idea of what happens in general, but the question comes up all the time, “How do I roast this?” this particular bean.  That’s coming up, but first,  Coffee Storage. We’ll get deeper into specifics about roasting, grinding, brewing, as we go. We’ll also discuss specific roasters.