Common Issues for New Roasters

This is an updated article from our blog archives. The original post is from March, 2017

While every roaster's coffee preference and roasting style may be different, many operators face the same challenges and issues when they first begin to hone their craft. These are a few of the most common issues we encounter for new roasters. 

Not using a full charge

Unlike many other manufacturers' machines, Mill City Roasters are designed to operate at 100% batch capacity. As long as you have adequate gas pressure, or power in the case of our MCR-2E, and your venting run does not inhibit airflow, you should acquaint yourself with your system by roasting at full capacity.

Once you've dialed in profiles for 100% charge weight, you can begin to create template profiles for charges at 90%, 75%, 50%, and so on. If you decide to charge at less than 50% of your machine's drum capacity, you may consider slowing your drum speed by a factor of 8-16 RPM to ensure that you maintain the recommended amount of contact between the coffee seed and the drum wall. 

Relying too heavily on saved roast profiles

Data logging software is a tool, but it cannot account for daily changes in temperature, humidity, and (most importantly) the age of your green coffee. Software is intended to assist your eyes, your ears, your nose, and your palate. Trust yourself. Learn to cup!

We recommend doing several roasts without software, especially when working on a new machine. This allows you to focus on the sensory cues and also prepares you for the inevitable failure of a laptop crashing mid-roast. If you're comfortable roasting using more analog tools like pen and paper, you won't panic when your digital tools fail you and you have a few dozen pounds of nice greens in the drum. 

Using a soak on larger roasters

In many of our roast-along videos on YouTube and in our roasting templates that we share with students in our Roasting 101 courses, we recommend a soak at the beginning of the roast. This is a short period, 30-60 seconds, at the start of the roast, where the burners are turned off. There are many reasons for soaking, but the importance is that it's a useful technique on smaller roasters.

Using a soak on 3kg machines and smaller can help you control the dry phase and make the start of your roast more predictable. On larger machines, it can stall your roast or limit your ability to control when your early landmarks occur. Many newer roasters will assume that because they've seen it demonstrated, using a soak is the best practice. That's not the case. If your machine is on the larger side, or your available gas pressure is less than what's recommended for your machine, soaking will unnecessarily elongate your roasts and can diminish your coffee quality. 

Failing to cup

You have to cup your coffee. Schedule a set time for cupping and stick to that schedule consistently. Cup every week, at least one day each week. Cup consistently; use the same ratios, grind size, and brew time each time you cup to eliminate variables. 

Learn what profiles are working for a coffee and which ones can be tweaked to improve the cup. Cupping also helps you expand your palate, clarify vocabulary, and discover flavors that are specific to countries, regions, and processing methods. Find 3 others who wish to learn coffee. Cupping in a group leads to exponential learning.

Misunderstanding and misusing airflow

Many new roasters and installers erroneously believe that the only role of airflow in a roaster is to remove smoke and combustion gas from your roasting facility. In specialty coffee, airflow is also an important variable in how roasters control their roast and fine-tune coffee flavor. Airflow impacts how heat moves into the drum and, similarly, how heat transfers to coffee beans. 

Every installation is different, meaning airflow settings do not translate from one system to the next. Use the lighter trick to discover your roaster's settings for low, medium, and high airflow. During your roast, move from lower to higher airflow settings as your roast progresses. 

It surprises people to find out how much poor control of airflow can impact a roast. It's one of our most common "fixes" for myriad issues we troubleshoot with our customers. If your roasts taste dull or smoky even at light and medium levels, it's probably an airflow issue. If you can't seem to get a handle on your drum gap and experience drum rub during your roast, look at your airflow. If your roasts run too fast in development and the coffee tastes underdeveloped even at darker roasts, you might have an issue with airflow. 

Choosing the right charge temperature

Understand how specific coffees take heat by paying attention to patterns in roasting. Higher-density coffees, washed coffees, and small seeds can typically take higher charge temperatures. Natural processed coffees, honey processed, decafs, larger seed sizes, pre-blends, and less dense coffees will be happier at lower charge temperatures. 

You may also find that your charge temperature changes when your batch size changes drastically. Take note of charge temperatures that work well at certain batch sizes and remember to adjust as needed. 

Variations and mottling in roast color

Some coffees, like natural processes, will have a mottled appearance at lighter roast levels, which is fine. Lower-priced coffees that have a mix of seed sizes and ripeness levels will likewise have an uneven appearance after roasting.

If your higher-quality washed coffees have a lot of variance in roast color, your drum speed may be too slow. Looking through the sight glass in your roaster's faceplate, you should see a 45°-55° slope in the coffee pile gathering on the left side of the glass. Adjust your drum speed until you achieve that slope. 

The need for better greens

The number one determining factor of the quality of your roasted coffee is the quality of your greens. You cannot roast an 80-point coffee to taste any better than 80 points. If you are cutting costs on your greens, your roasted product will suffer. 

The world's best chefs and bakers already know this: when your recipe is simple, the ingredients matter more. Coffee is the most simple recipe, and your green coffee is the only ingredient. Invest more money in your greens and you buy yourself a larger target to create something delicious. 

Need help? Call us to chat, we love to talk about coffee.