The Lab

Troubleshooting Your Roast

After receiving a new coffee, we can develop a plan for roasting it based on the coffees origin, variety, processing style, density, and moisture content. For more information about starting to roast, see our post here. After that first roast, odds are there is some room for improvement, but how do you know what to adjust and why? Here are some tips for altering your roast based on the flavors you observe after cupping.

Coffee roasted too dark, unless that’s what you like!

Smokey and Ashy

This is the most easy to identify, and in a lot of cases, you can tell a coffee is roasted too dark just by looking at it. When cupping, this coffee will taste ashy, smokey, rubbery, and oily in the extreme cases. If the coffee is only slightly too dark, you will notice a heavy body, more caramelized or burned sugars, some woodiness, and decreased acidity.

If your coffee does not look too dark, try looking closely at each bean. If you see small dark spots or small beads of oil, especially on the flat face of the bean, this is a sign of the roast defect known as scorching. When coffee is added to a drum that is too hot, the surface of the bean that comes in direct contact with the drum will burn quickly. To avoid scorching, decrease your charge temperature or increase your soaking period. A soaking period is charging the coffee into the drum with the gas on its lowest setting or completely off. This will help decrease the difference in temperature between the drum and beans to prevent any searing or scorching, while still maintaining enough energy for ideal bean development.

If the roast is not too dark, and there is no scorching, there was too probably not enough airflow. Air flowing through the drum will help carry burning chaff and smoke out of the roasting chamber. Increasing the airflow will help decrease smokey flavors, especially around yellowing when chaff begins to separate from the beans.

Clear scorch marks during yellowing that may be masked at medium and darker roasts

Grassy and Grainy

As specialty coffee roasters and consumers, we tend to err on the side of too light, especially with our first roasts. Coffees that are too light will be grassy and grainy, because starches/carbohydrates did not reach the appropriate temperature to be broken down into simpler sugars by caramelization. Increasing the end temperature will force those compounds to breakdown and caramelize resulting in more body and sweetness.

Coffee roasted too light, unless that’s how you like it

Intensely Sour

Sourness is a result of coffee’s acidity, and if it is too intense, your roast was likely too short. Extending you development time after first crack will cause some of the acids to break down and will develop more supporting sweetness that can make intense acidity more palateable.

Green and Vegetal

Savory and green flavors like seaweed or vegetables is a sign that your roast was under-developed or heat transfer through the center of the coffee was inadequate. The color on the outside looks right, but the internal bean is likely a bit lighter. This is more likely to happen in higher moisture coffees where greater energy is required during initial drying phases. More gentle heat application and extending the time spent in green/yellow sections of the roast will help dry the coffee thoroughly and eliminate remaining vegetal flavors.

There are some varieties like Pacamara and Parainema that are more prone to develop these flavors as well. More gentle heating and extending the length of the roast will help to round out those flavors.

Check ground color vs whole bean color. If there is a large difference, the coffee is likely underdeveloped

Peanut and Buttery

Another sign of under-development is overwhelming peanutty and buttery flavors. This is most common in naturally processed or low-density coffees that are roasted too quickly. Low-density coffees tend to also have lower starting acidity and naturally processed coffees tend to have higher concentrations of lipids and complex carbs so the nuttiness and buttery flavors may be dominant. Stretching the time to first crack will allow for more even heat transfer through the bean and increasing the development time and end temperature will transform those flavors into sweetness and body.

Low Acidity

This is an indication that your coffee was in the roaster for too long after first crack or that first crack took too long to occur. Acids breakdown as the roast progresses, especially after first crack when the amount of water in the bean is lowest. A long development-time will cause the acids to degrade, while sugars caramelize and oils combine at the surface of the bean masking any remaining acidity. Decreasing the development time in the roaster post-first crack will preserve more acidity and reaching first crack more quickly will make acidity more pronounced in the cup.

Flat – lacking sweetness, acidity, and body

This is most commonly known as ‘baked’ coffee. When a roast is too long, acids and sugars will completely break down. If the roast is also light or medium, there will also be very little body as well. The best remedy is to decrease your total roast time.

When fine-tuning your roast, it is important to change only one variable at a time, at least at first. Changing multiple aspects of the profile will make it difficult to draw a clear conclusion about what is causing the flavors you experience. As you roast and cup more coffees, it will be easier to notice which parts of the roast are causing certain flavors. For more help with roasting and profile development, contact the Lab by Royal NY.

Patrick McKeown

Patrick began his coffee journey on Long Island at a small coffee bar and roasting at home. Since then he has been a barista, manager, and craft roaster in NYC.