An Intro to Coffee Roasts

Here's an introduction to why roast levels in coffee make it taste so good.

So, what's the difference between dark roast, medium roast, and light roast?

Coffee beans grow on trees, but unlike fresh fruit, they have to go through a few processes before they become the brew you know and love. Once the beans are processed at coffee farms and mills, they come to us in a raw—or green—state. In that state they are stable, but not yet ready to be ground and brewed.

First, they need to be roasted, and how coffee roasts are done matters a lot to the final product. 

Coffee Roasts Explained

Roasting is the development of flavor. In some ways, this is no different than what happens when you cook at home. Just as when you sear a steak or bake bread, the application of heat browns the food and deepens the flavor. This is called the Maillard reaction. The same happens to coffee beans in the roasting process.

Of course, terroir (the character of the area where the bean is grown), process, and species factor in, but the type and precision of the roast has the single greatest impact on the flavor in your cup. That’s why we place such an emphasis on skill. Execution is everything, and we pride ourselves on our expertise. 

Types of Coffee Roasts

Coffee beans are generally narrowed down to three roast types: light, medium, and dark.

During the roasting process, the beans undergo changes in color, aroma, and flavor. Making the judgment call on when to pull a roast to accentuate the best characteristics of a bean is the roaster’s ultimate goal and requires using all five senses.

In general, lighter coffee roasts retain the fruitier characteristics of the bean (which is, after all a fruit), and darker coffee roasts bring out more caramel and cocoa notes.

Coffee Roast Levels

Everyone knows their favorite coffee roast. In fact, perhaps above all other coffee subcategories (region, process, coffee tasting notes), roast level may be the descriptor that people use to share their coffee preference the most. But how can you really tell what roast level a coffee is, or what it says about the coffee? The first cue is visual. And while specific tasting notes, like chocolate or stone fruit, are most tightly aligned with the coffee’s origin, roast level still affects flavor. Below we’ve outlined the spectrum of coffee roasts:

• Under-roasted coffee beans are pale green in color with a raw, grassy aroma and taste. The flavor profile and body of under-roasted coffee is considerably weak.
• Light Roast coffee beans are light brown in color with a lustrous quality. They have a floral aroma with hints of bright fruit. The flavor profile of light roast coffee is tart, vibrant, and light bodied.
• Medium Roast coffee beans are medium brown in color and appear shiny. They have a toasty, fruity aroma. The flavor profile of medium roast coffee is balanced and smooth.
• Dark Roast coffee beans are dark brown in color and appear glossy. They have an aroma ranging from cacao to toasted nuts to caramel. The flavor profile of dark roast coffee is bittersweet and full-bodied with hints of caramelized sugar.
• Extra Dark Roast coffee beans are deep brown in color and very glossy. They have a smoky, brûléed caramel aroma. The flavor profile of extra dark roast coffee is robust and full-bodied with hints of heavy-bodied sugar.
• Over-roasted coffee beans are black and appear quite dull. They have an ashen, scorched aroma. The flavor profile of over-roasted coffee is bitter and metallic. 

How Long Does It Take to Roast Coffee

Aside from the level of the roast, there are many factors to consider when determining the correct amount of time to roast a batch of coffee. Depending on variables like volume of beans and type of machine, country of origin, and elevation at which the beans were grown, you can reliably count on a single batch of coffee taking somewhere between 10 to 20 minutes. Once the green coffee is dropped into the roaster and begins to heat up, you can observe what’s known as a “roast curve”: A quick drop in temperature as beans are introduced to the heat environment, followed by a slower, incremental climb in temperature as the batch begins to brown. When observed on a screen, this looks a little like a Nike swoop. The trajectory of this curve contains important milestones which a roaster will keep eyes, ears, and a nose out for to track the progress of their roast. Roasting coffee well involves all senses.

1. When the coffee reaches around 380-400℉, the beans will begin expanding which makes a small “popping” sound, not unlike popcorn. This is called “First Crack” and is an indication that the coffee is starting to brown, and flavors & aromas have begun develop. If you are going for a light roast, you might consider pulling your beans from the heat around now. 
2. If a medium roast is the goal, then don’t sit back down just yet. At this point in the roast, the physical and chemical changes are happening quickly, and a great roast will require close attention. Medium roasts are notoriously subjective, so anytime between first crack and the imminent second crack (we’re getting there!) is fair game to hit the brakes on the heat.
3. As we creep up to 430-450℉, we approach what is known as “Second Crack”. This louder and more intense popping sound is an indication that the bean is beginning to cellularly break down, releasing gasses and oils which were trapped inside. We are officially in dark roast territory and will want to pull the beans from the heat before the second crack has died down. 
4. At Peet’s we are not afraid to take our roast to the limit, because we always preserve the integrity and character of our coffees. Getting to this point takes expert timing and skill to avoid scalding the beans, which continue roasting before they are pulled. However, we don’t push it too far: our skilled roasters train for over 10,000 hours, so they can sense nuances of the roast down to the millisecond.

How does coffee roasting affect caffeine?

There is virtually no difference in caffeine content between light and dark roasts—by weight. However, the more you roast the beans, the more they dry out, making them less dense than lighter roast beans. Consequently, a scoop of light roast beans is denser, and therefore has more beans, than a scoop of dark roast. If you want to get a consistent amount of caffeine, measure your coffee by weight. Note that we say consistent. Caffeine content can vary.

Are there industry standards for dark, medium, and light roast coffee?

Roast definitions are not standardized in the coffee industry. What one company calls a medium roast, another company might call a dark roast. What we call a light roast, others might call medium. Peet’s roasts have always skewed darker, because we like caramelized sweetness and body in our coffees. Extra-dark roasts, a style pioneered by Alfred Peet, are more roast-forward in taste. Peet's medium roast coffees are crafted to be exceptionally balanced and smooth. And when we say crafted, we mean it. Because we believe in finding the best roast profile for each coffee.

Above all, it takes great skill to usher a bean through roast development properly. Whether you drink a light, medium, or dark roast, the greatest difference you will taste is whether a coffee was roasted well or roasted poorly.

Which coffee brewing methods are best for light, medium, and dark roasts?

Since the flavor profiles of each roast are so different, brewing is key to the experience. Lighter roasts respond well to pour over and Chemex, as they accentuate the bright acidity and floral aromatics. Medium roast, with more of a balance of fruity and spicy notes, is an all-around performer, as comfortable as a cold brew as it is as a pour over. A French Press, also known as a press pot, can bring out the body and depth of a well-crafted dark roast, and espresso absolutely demands a dark or extra dark roast to showcase those rich chocolate and nutty flavors. But everyone’s taste is different. Try different roasts with different brewing methods and see what works for you.