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Inside the Coffee Roaster

Inside the Coffee Roaster

What actually goes on inside the coffee roaster? In short, green (un-roasted) coffee goes in and roasted coffee comes out. However, if it was that simple, everyone would be doing it.

A coffee roaster is a large, gas powered oven that spins and relies on air circulation to effectively roast coffee. Once the green coffee enters the hot

Inside the roasting drum.

roasting drum, that’s when the magic begins to happen. This is where us coffee roasters take a great bean and make it even greater by honing our craft and closely monitoring what goes on inside the coffee roaster. If it weren’t for this last but crucial step, all the hard work of the coffee farmers would be all for naught.

Receiving a new crop or origin begins by trial and error, finding out what attributes are most brought out by certain temperatures, roast times and cupping notes. Then we determining whether or not it will stand alone as a single Origin or will serve better in a coffee blend. The traders will offer cupping notes, but depending on each roaster’s experience, equipment and technique, results may vary. Just because the bean is quality, it is all a matter of what goes on inside the coffee roaster.

From Coffee Research, there are four basic elements that come from roasting coffee to get to number 5, the flavor:

  1. Aroma – This is the result as the nose is first exposed to the wet grounds.  When smelling coffee, the aroma can help you evaluate the coffee flavor and the brightness of the coffee.
  2. Acidity – Is the bright and dry taste that adds life to a coffee.  Acidity in coffee does not necessarily correlate to the pH of a coffee, that would upset your stomach, but is believed to be the result of the acids present. The acidity of coffee is akin to the dry but bright sensation experienced on the back sides of your tongue.
  3. Body – Body is the weight of the coffee that can best be sensed by allowing the coffee to rest on the tongue and by rubbing the tongue against the roof of the mouth.  Coffee body ranges from thin, to light, to heavy and is a result of the fat content.  Lighter coffees tend to have a light body while Medium and darker roasts will have a heavier body, but conversely will have less acidity.
  4. Aftertaste or Finish – Aftertaste is the sensation that is experienced after the coffee is swallowed.  It is the lingering remnant of the coffee taste that often changes over time.
  5. Flavor –  is a term that encompasses all of the other coffee cupping parameters.  It is an overall evaluation of the coffee taste.  The Specialty Coffee Association of America  created a coffee flavor wheel, which is used as a helpful guide during coffee cupping.  The full poster is in color and includes another wheel to describe flavor and aroma taints.

When the green coffee is charged inside the coffee roaster, the endothermic reaction begins as the beans turn and evenly take the heat in. The beans will change in color form green to yellow and you may smell what is likened to toast, popcorn, or hay as the moisture begins to leave the beans.  Form there, the internal temperature of the roaster will rise as the beans take on more heat and reach the second milestone, the First Crack.

The sound of the first crack means the water has escaped from the bean, and the outer shell will change it’s structure from the heat. At this point the beans become a lot lighter in density as the water escapes, and the beans will also increase in size as a result. This is the beginning of the end of the roasting cycle and what goes on inside the coffee roaster from this point is critical. At this point, a light roast is born offering more of the coffee’s origin flavors and subtleties in their tastes. Also, a light roast will have more  caffeine. Depending on the quantity, bean size, bean age, origin, and moisture content this can be from 375-400 degrees.

Quickly followed comes a quick rise in temperature and this is where you can go from medium to burnt in a matter of minutes if you do not watch your craft. The sugars in the bean react to the heat and begin to change their structure and the roast profile begins to gain body. At this point, there are some different takes on what determines when the coffee is finished. Some roasters will go by temperature, others by sight and their own instincts and senses. Regardless, this is when the art of the science comes into play and you will net the results discussed above from medium to dark roasts.

After the second crack, there is little moisture left in the bean, and the effect is more of the roasted flavor over anything else, losing predominant origin notes with a bigger body. Once you pass this point, oils will be released from the bean resulting in a French Roast – “Dark brown, shiny with oil, burnt undertones, acidity diminished. At the end of second crack. Roast character is dominant, none of the inherent aroma or flavors of the coffee remain” – from Wikipedia for more roast profile information, please click on the link.