November 27, 2020

Eight Common Mistakes That Home Coffee Roasters Should Avoid


Those who roast coffee at home know that it can go from a simple hobby to an all-encompassing obsession in a matter of weeks. There is nothing like drinking a cup of fresh, delicious coffee at home and knowing that you’re the one who roasted it. 

However, experienced home roasters will also know that it comes with something of a steep learning curve. There are a number of common pitfalls and obstacles that many people fall prey to time and time again.

To learn more about these common mistakes, we spoke to Royal Coffee’s Evan Gilman. Read on to find out what these mistakes are and look at how to avoid them.

You might also like Roasting For Filter And Espresso At Home

Mistake #1: Not Preheating Your Equipment

Depending on where you are roasting, or what time of year it is, your equipment’s temperature will naturally fluctuate. Setting out a preheating routine will help you ensure consistency when roasting a few batches. 

“You should always preheat your equipment before roasting,” Evan explains. “This allows for better consistency when you charge the roaster with green coffee, and you can be sure the temperature reading you’re getting is the actual temperature of the roaster. 

“When roasters aren’t preheated, the heat can [end up being] unevenly distributed.”


Mistake #2: Not Taking Notes

Roasting coffee at home understandably involves repeating a number of routines and procedures, so it might be easy to think that you’ve got it all committed to memory. However, without proper documentation, you might find that the next batch of beans tastes wildly different to the last. 

Evan explains that taking detailed notes is very important. “When I roast, I log temperatures from the beginning to end, starting with the charge temperature and ending with the temperature when I drop the beans out of the roaster and into the cooling tray. I also record all changes to heat application and airflow. 

“If you’re using a program like Artisan or Cropster, you can annotate these changes, and temperature will be automatically recorded throughout the entire roast. If you’re documenting temperature by hand, I would recommend at least every 30 seconds, if not more often!”


Mistake #3: Rushing To Drink Your Coffee

After you’ve finished roasting, it can be hard to stop yourself from immediately tasting your latest batch. While freshness is important, roasted coffee needs to release CO2 before it is truly ready to drink. 

Every batch will act differently; the amount of time it will need to be rested for depends on a number of different factors, including roast profile, variety, and altitude, just to name a few.

Evan tells me that he has found that finding a “sweet spot” when resting your beans will allow you to taste the coffee with a lot more clarity. “I like to let my coffee rest for a few days after roasting; ideally, at least five days. A good rule is to drink darker coffees [more quickly], and let lighter coffees rest for longer. 

“[Resting is important] because there is residual CO2 trapped in the cell walls of the coffee. This CO2 releases on contact with water, and can interfere with the brewing process. However, you don’t want to lose all your CO2, since this gas also helps to carry away volatile aromatics.”


Mistake #4: Under & Over-Roasting

This common home roasting mistake is one of the hardest to get right. Knowing what you are looking for in your roasted coffee will help you to identify what coffee will look like when it’s under or over-roasted.

It’s important to note that these are very fine lines with home roasting. Sometimes, it will come down to personal taste. 

Evan says: “There are some signs you look for to tell if your coffee has been under-roasted or over-roasted. Physically, under-roasted coffee will be lighter, and you won’t be able to crush it with your thumb when pressing up against a table. 

“Over-roasted coffee will be covered with oil, and if extremely over-roasted, you could even write or draw with it since it has been reduced to carbon!

“In terms of flavour, under-roasted coffee can be grainy or bready tasting, with a sort of brothy consistency when brewed. Over-roasted coffee will be quite thin when brewed, and will taste quite bitter.”

Learning to avoid fundamental mistakes like this takes time. While there’s no substitute for experience with home roasting, there are a number of educational resources and courses out there for people who want to learn more. 

One such example is The Crown, an open-source coffee education centre based in Oakland, California. As well as operating a “tasting room” and coffee lab, it also provides online coffee resources and hosts regular webinars.

Mistakes 1

Mistake #5: Not Understanding Your Green Coffee

When you’re sourcing new coffee for home roasting, it can be hard to build a roast profile to match. The more details you know about a coffee (variety, elevation, processing, and so on) the better you’ll be able to roast it. 

Evan tells me that small variables make a huge difference, and that no one green bean is the same. “Every bean will be different. Learning the little idiosyncrasies of each coffee you work with is half the fun.”

He gives me some basic tips: “Coffees with a wider spread of screen sizes will take longer to heat up in the roaster. Coffees with a lower density will take on heat more easily at the beginning of your roast. High-density coffees, however, can take on heat later in a roast, and fly through post-crack development. 

“Coffees with high moisture content will need more energy to get to first crack. [I even find that] sometimes Kenyan coffees [reach first crack] earlier than any other origin. There’s an infinite number of these little differences, and it just takes time to get used to them. This is where taking notes really helps.”

However, beyond note-taking, there is no substitute for simply roasting a lot of different coffees from a range of origins. While often the minimum order size for green coffee can be comparatively high for home roasters, some suppliers have started providing lower minimum order sizes to cater for this audience. Royal Coffee, for example, recently launched 1lb bags of green coffee as part of their Crown Jewels range.

Mistake #6: Baking Beans

“Baking” is a common term for a roast defect that can destroy the complex flavour profiles contained within green coffee. If heat is taken away from the roast at the wrong time, the temperature of the bean can stall, rather than changing as it should.

Evan explains how baking happens. “The general consensus is that ‘baking’ occurs when your rate of rise (degrees per minute) either stalls or drops to a negative late in your roast, usually before first crack.

“This means you’re either keeping coffee at the same temperature or losing temperature before you have properly developed the sugars in your coffee.” 

And how do you avoid it? Evan says: “Avoid stalling your temperature before first crack, and you’re likely to avoid baking, though you can also bake a coffee out in post-crack development [if you’re not careful].”

Mistake #7: Scorching

While baking occurs when the rate of rise stalls or drops, scorching occurs when we use too much heat in the early stages of the roast. When a bean is scorched, it burns on the outside while the inside remains raw. 

Evan has experienced this first hand. He gives us some advice on what to concentrate on to avoid scorching. “Scorching happens when a coffee takes on heat too fast in the beginning of a roast. High charge temperatures can scorch your coffee by cooking the outside of the coffee to a crisp before allowing heat into the center of the bean. 

“Too much heat at the beginning of a roast is almost always the culprit here, but you can also scorch a coffee later in roast by applying too much heat too quickly. Watch for this in roasters with very powerful burners.”

Mistake #8: Not Keeping Your Equipment Clean

While many of these mistakes will lead to little more than bad-tasting coffee, home roasting equipment that isn’t properly cleaned can be highly hazardous.

As well as cleaning your home roaster regularly, you should also keep a vacuum cleaner close at hand to ensure the area in which you roast is clean and tidy. Chaff in particular is highly flammable. 

Evan has worked professionally as a roaster, and he tells me that the importance of good health and safety procedures cannot be understated. Seemingly harmless waste can become dangerous if it is ignored. “The biggest danger is fire,” he explains. “When chaff accumulates anywhere, it [becomes a major fire hazard].”

He adds that this is a bigger problem with certain coffees. “The ‘chaffiest’ coffees I’ve experienced are always natural or honey processed coffees,” he says. “With these, the silverskin is still often clinging to the bean a bit because of the processing method that has been used. There is less to worry about with most washed or wet-hulled coffees.

“Remember to clean all the time, too, just like you would in a commercial kitchen. It might already look clean, but it never hurts to clean up just a little more than necessary.”

As well as this, keeping your equipment clean will help you avoid having anything left over from previous roasts that affect the flavour of your next batch.

Honing your skill as a home roaster takes time. However, eliminating some of these mistakes will put you in a great position to roast a variety of different coffees and unlock their true potential. They will also lead to greater consistency and repeatability when you roast. 

While everyone will have different techniques, there is no substitute for experience and hands-on time when roasting coffee. Keep practising, taking notes, and working with a variety of different green beans, and soon enough, you’ll be able to taste the difference.

Enjoyed this? Then read Five Questions Roasters Should Ask Their Green Coffee Importer

Photo credits: Nicole Motteux, Oscar Jimenez, Neil Soque, Josef Mott, Bax + Towner

Please note: Royal Coffee is a sponsor of Perfect Daily Grind.

Perfect Daily Grind

Want to read more articles like this? Sign up for our newsletter!