WHY IS A COFFEE BEAN JUST A TINY TEST TUBE?

GREEN (UNROASTED) COFFEE IS NOTHING YOU’D EVER WANT TO CONSUME. IT IS HARD ENOUGH TO BREAK A TOOTH, AND ITS TASTE LEAVES AN AWFUL LOT TO BE DESIRED. IN ORDER FOR IT TO BECOME SOMETHING WE CAN GRIND AND BREW,

FIRST IT MUST BE ROASTED. ROASTING COFFEE, AS IT TURNS OUT, INVOLVES SOME PRETTY COMPLICATED CHEMISTRY.

When we visualize chemistry, it is quite common to picture a laboratory with test tubes and various pieces of equipment. 

Mix the contents of two test tubes together and bam! Something new is created! Rule number one about chemistry: 

if chemicals aren’t in the same space physically, then they can’t react with each other. Rule number two: sometimes, chemical reactions need a little help getting going and being sustained. 

This help can come from external energy (heat, typically) or an enzyme (a molecule that facilitates chemical reactions without being used up in the reaction and without requiring much, if any, energy to push the reaction forward). 

Roasting coffee satisfies both those rules. The bean itself is the laboratory and the cells that make up the bean are the test tubes. The cell walls and the material within the cells comprise the raw ingredients of all the chemical reactions that take place during roasting. 

Roasting provides the energy source that begins and sustains the chemical reactions. While there are enzymes of all sorts in the cells, their role in the creation of what we know of as coffee is poorly understood. Most likely, enzymatic reactions don’t play a significant role in producing the coffee we know and love.

Actually, a coffee cell is more than just a test tube—it is also a pressure cooker. Plant cell walls are thick and durable. Thus, when the contents strive to get out, they cannot do so easily. 

When the cell becomes heated up from roasting, some chemicals change from liquids to gases and some new gases are formed. These gases will take up more space than they did as liquids or solids, so they push against the cell walls, creating pressure, just like a pressure cooker. While the cell walls eventually break from the pressure (more on this later), the increased pressure conditions do help shape the roasting process.