Posted by Emily Corley

Ever wondered how your coffee gets from a hard, green seed to the delicious, aromatic bean you’re familiar with?

When a facility receives green (unroasted) beans from a source, they get roasted and turn into the beverage we all know and love: coffee. But how?

You can thank the ever-so-talented roastmasters at facilities all over. Whether they’re using traditional drum roasters, or the more modern air-roaster, they know the slight nuances of the coffee inside and out.

When the beans go into the roaster they are subjected to high temperatures that cause some dramatic chemical changes. The first phase of roasting is all about heat, with the initial goal of reducing the moisture content through endothermic reaction (heat contact). The color compounds in the bean begin to break down at this point, changing the bean from a green color to a golden color. The green aroma associated with green beans also takes off around this point, and is replaced with a more toasty smell.

As the temperature rises, the moisture in the bean begins to create steam. The steam within the bean starts to build pressure, causing it to eventually (and audibly) pop. This is referred to as “first crack” and is a very important stage. Typically, the coffee will nearly double in size at this point and begin to develop that quintessential “coffee smell.” The beans will have gone from about 10-12% moisture to about 3-5% moisture by this time.

During this phase, the coffee is considered “lightly roasted” and can now be removed, cooled, and consumed. A little bit more heat gets you passed the first crack and a little darker. To get a medium roast, the roastmaster will allow the first crack to fully finish and keep the beans at a stable temperature for longer.

You could keep going if you wanted to.

Let’s keep going.

The next phase in the roasting process comes along with another endothermic phase in which the beans are slightly heated again. After this an exothermic phase (heat release) takes place, and yet another audible pop. Take a guess at what this is called.

Did you guess, “second crack”?

Well, you were right.

This time the popping is caused by the structure of the bean being rapidly broken down and various gasses forming within the bean. The oils within the coffee make their way to the surface; giving the beans that shiny appearance you’re likely familiar with.

Medium to dark roasts are finished right before or just as the second crack is beginning and you’re getting a fairly dark roast if you let the second crack continue, and a French roast as it’s ending.

Shall we keep going?

No. We should not.

Too much longer will cause the coffee to fully combust as it is essentially fully carbonized. Sad face.

So, now you know what the wonderful roastmasters at your local coffee roasters are so very familiar with. It’s a very scientific and well-tested process and, in my opinion, one of the most important jobs on the planet because: coffee.