May 29, 2019

The ABCs of Coffee Roasting

Regardless of how it first began, coffee roasting was a revelation to the world. Some believe it started with a burning tree. Others think a hungry man threw some beans into the flame and softened them with water to try and make the edible. In any case, it was through experimentation, luck, and more than just a little bit of ingenuity that our ancient ancestors discovered that coffee beans are incredibly soluble when roasted, and that this simple combination – hot water and roasted beans – produces an invigorating drink with an intoxicating aroma, and surprising complexity.

Today’s coffees are no longer roasted solely based on smell and sound, as they were in the olden days, but with the help of spectrophotometers, specialized electronic temperature control, and complex systems designed to produce top quality at an inhuman rate of consistency. Coffee roasting is much more involved than just throwing beans into a pot, although that is essentially how it started. To get from the first coffee cherry to the final product – that delicious package of freshly-roasted and vacuum-sealed beans – you have to be willing to go through a series of steps.

Preparing the Beans for Coffee Roasting

Before you get to roast coffee, you must get to the beans. Coffee doesn’t grow in a pod, nor does it grow as a bean – instead, coffee beans are the green seeds of coffee cherries, which grow on coffee trees (which, in most cases, only grow to be roughly bush-sized). Coffee cherries taste much like other berries, with a slight tang and a touch of sweetness, as you’d expect from currants, cranberries, or mulberries.

But it’s not the berries or cherries that most farmers are interested in. While there is a small market for coffee cherries, these are usually sold dried if at all. In most coffee plantations, three methods are used to separate the seeds (of which there are usually two) from the pulp and mucilage of the cherry. These methods are:

  • Dry: This involves picking and laying coffee cherries out to dry over several weeks. The cherries are raked every few hours to ensure an even drying process, and cherries with a high-water content are not processed this way to minimize the growth of bacteria and fungi in the cherries. This produces a bolder taste after coffee roasting.
  • Semi-Dry: This involves wet washing or processing the cherries through a pulping machine, to remove the pulp and most of the mucilage, before setting them out to dry in the sun or in a drying machine. This process produces a more acidic flavor profile after coffee roasting.
  • Wet: This process is common in South America and produces the most acidic flavor profile. It involves wet washing the cherries until only the beans are left, completely rinsing off any pulp or mucilage.

How Coffee Roasting Works

Just like a good slab of meat, fire does something wondrous to coffee beans. While a cup of brewed green coffee beans would taste slightly sour and very grassy, roasting and macerating (grinding) the beans before brewing them allows you to release a number of volatile and highly specific naturally occurring chemicals within the bean. They’re ‘volatile’ because they dissipate quickly, which is why coffee has this wondrous aroma and goes stale with time. Most of these delicious chemicals come in the form of oils found within the bean, as well as sugars and other compounds created in reaction to the heat the beans are exposed to during the coffee roasting process.

Coffee is roasted in a giant metal container with a mechanical arm continuously stirring through the beans to ensure that none are roasted for too long, or that the roast turns out uneven. What coffee roasters look for when roasting a batch of beans is a distinctive and deep crack, similar to the sound of popcorn popping. This crack signifies that most of the moisture left in the green coffee bean has evaporated.

What Color Says About Coffee

At this point, the beans will have gone through a change of color from green into mottled yellow, light brown, and finally, a consistent shade of brown with no mottling. Further coffee roasting eventually leads to a second crack, which is much higher in pitch, and means that the coffee is close to reaching its final stages. Leaving it to roast for much longer past this point causes much of the sugars and oils in the beans to dissipate and burn entirely, leaving behind a bean that begins to taste like ash, until all the beans are turned into pieces of charcoal. At this point, each individual bean is little more than pure carbon, perfect for starting a huge fire.

From Light to Dark

Coffee is roasted to different levels depending on taste, somewhere between a point just before the first crack, and a point just after the second. The longer the beans are roasted, the more the flavor profile changes from acidic and fruity to chocolatey, bold, and strong. Some darker roasts are more bitter than others, and that has a lot to do with how close the beans are to being burnt.

Medium roasts sit comfortably in the middle, with complex flavor profiles and a certain sweetness and acidity to them. They’re not as acidic as the light brown light roasts, but they’ve still got a hint of what the bean was like when it was still a pit in a coffee cherry. The sweetness comes from the glucose in the bean reacting to the heat of the roasting process, kickstarting the Maillard reaction (this is what happens to meat when you brown it).

Finding the Right Coffee Roast

Taste is everything when it comes to coffee roasting. Don’t shame others for their coffee roasting choices, and don’t worry about what kind of coffee you like. No, you don’t have to love ‘that amazing Costa Rican light roast” if you just don’t enjoy the fruity or floral flavors in your coffee, and your friend isn’t wrong for preferring a dark roast over other, subjectively ‘higher quality’ beans and roasts. Some people like their coffee light, others like it strong.

As long as you’re not drowning the flavor of your coffee in a pile of sugar and half a cup of milk (at which point there’s very little coffee left in your coffee, and it’s become a coffee drink), you’re entitled to enjoy your brewed cup of joe however you wish, and thankfully, there’s a massive variety of roasts and beans for you to try out and enjoy. One important piece of advice, though – please do try everything. Have a cup of coffee from every major coffee producing country in the world. Try light, medium, and dark roasts. Try them brewed in machines, cafetières, and Moka pots. Find the bean and roast that’s truly right for you.