Roasting coffee to bring out its best characteristics is a fine art, but also an exact science. There are many steps to the process, and each one requires precision and care as even minor mistakes can affect an entire batch.
The process, however, doesn’t stop once the coffee leaves the drum or roasting chamber. In fact, the cooling stage has a huge impact on overall cup quality and flavour profile, yet is often overlooked. So what do roasters need to know to achieve the results they want?
Simo Kristidhi, production manager at Solberg & Hansen and 2022 World Coffee Roasting Championship runner up, and Ben Morrow, co-founder of Manhattan Coffee Roasters and two-time Coffee Masters Champion, provide their insight on the best ways to cool roasted coffee.
You may also likeour article on how convection coffee roasters work.
Cooling coffee: The final roasting step
When we talk about coffee roasting, we often focus on the development stage, which is when flavours and aromas form. This phase is in four parts:
- Drying – beans lose moisture and water
- Maillard reaction – amino acids and reducing sugars react to create melanoidins, which give browned food its distinctive flavour
- Strecker degradation – amino acids react with carbonyl-grouped molecules to form aldehydes and ketones, which are critical to develop flavour and aroma
- Caramelisation – complex carbohydrates break down into simple sugars to enhance sweetness
All the above steps take place inside the drum or roasting chamber, but the process doesn’t end there. Cooling roasted coffee is considered just as important as what happens inside the machine, and plays a significant role in overall taste, body, and aroma. When carried out inadequately, the efforts of the entire supply chain can be undone.
Once coffee beans reach the desired profile, roasters need to cool them immediately to prevent further development, which could impair flavour and quality.
Simo Kristidhi has roasted coffee for Norway’s Solberg & Hansen for over 20 years. He has also competed at four Norwegian Coffee Roasting Championships, and placed second at the 2022 world finals.
“The cooling step decelerates the high speed of development that happens during roasting,” he tells me.
Why proper cooling is so important
As a result of high temperatures and constant airflow inside the drum or roasting chamber, coffee beans contain a lot of energy. This means that even when released from the machine, the chemical and physical structure of the beans will continue to change.
In cooking, we refer to this as “carry over”. Even if you remove ingredients from a heat source, they will continue to cook, including internally. Research indicates that carry-over cooking can increase the internal temperature of food by up to 8.6°C (or 15.5°F) beyond the desired level.
In the context of roasting coffee, carry-over cooking makes it all too easy to unintentionally overdevelop roast profiles, and potentially lose terroir and flavour.
How cooling practices have changed in specialty coffee
The best practice accepted in specialty coffee is to cool roasted beans to room temperature in ideally less than four minutes (and no more than five). This time period is usually sufficient for the internal temperature of the beans to drop to ambient levels, and prevent any further physical and chemical changes from occurring.
To achieve this, most machines (especially drum roasters) include a cooling tray with a perforated bottom connected to a fan system. The fan pulls air from the room while an arm stirs the coffee beans to ensure even cooling.
Ben Morrow is a co-founder of Manhattan Coffee Roasters in Rotterdam, Netherlands. He says that the machine’s cooling tray is integral to this process.
“Cooling trays are large and porous, so when beans are dropped into them, they expel water vapour,” he explains. “As the coffee beans rapidly cool and release moisture, their cell structure contracts and becomes denser.
“If coffee isn’t cooled to below 30°C (86°F) in the required timeframe, the beans will keep cooking, which makes them taste flat and less vibrant,” he adds.
Some years ago, quenching was a popular technique used to cool roasted coffee, and is still sometimes used in fluid bed machines. This practice involves spraying water directly on roasted coffee to expedite the cooling process.
“Over the last 15 to 20 years, fewer people use quenching as a cooling method,” Simo says. “Even when it is used, it’s generally only done for commercial-grade coffee and not for specialty lots.
“Quenching can add some undesirable flavour attributes to coffee, such as a flat, metallic, or leathery taste,” he adds. “New and upgraded cooling systems result in better flavour clarity, preserve more of the coffee’s terroir, and highlight the desired taste profile.”
How does delayed cooling impact coffee flavour?
Roasters develop specific profiles to bring out the best characteristics of a certain coffee, so cooling beans quickly means they achieve the results they want.
“Cooling coffee unevenly and too slowly can lead to unwanted development,” Simo tells me. “An excessive amount of oils could develop on the surface of the beans as they would still contain a lot of energy from high roasting temperatures. This will result in more bitterness and harshness, as well as fewer fruity flavours.”
Delayed cooling often leads to baked or flat flavours with noticeably less sweetness, largely because more of the sugars become insoluble.
So is there a best way to cool coffee?
Cooling with air is the most common practice in specialty coffee, but ambient temperature is still an important factor to consider. If a roastery is too hot or cold and not temperature-controlled (especially during warmer and cooler seasons), it can prolong the cooling process.
“Air temperature can also vary from place to place, so roasters at high altitude or in hot places need to monitor the temperature of their space more closely,” Simo adds.
Quenching, meanwhile, isn’t the preferred method. Although there’s little research to back the claim up, many believe the practice results in coffee beans reabsorbing small amounts of water. However, this only tends to be an issue with larger batches and darker roast profiles, whereas water droplets will evaporate more quickly on smaller-capacity machines and lighter roasted coffee.
“Fan cooling is the most cost-effective way to quickly cool coffee,” Ben says.
Tips for cooling coffee
With this in mind, there are a few key points that roasters need to know:
- Regular machine maintenance and cleaning are essential to make sure air cooling systems work properly
- You should programme cooling arms to turn at optimum speed and number of rotations
- If the arms move too quickly or rotate too many times once the coffee starts to cool, it can unintentionally prolong the process
Many roasters agree on the four-minute cooling window, but there are many factors to consider in the final step of the roasting process. In addition to room temperature, the age and bean density of coffee will affect the rate of cooling.
“We need further research to understand how the speed of cooling impacts flavour and cup quality,” Simo concludes. ”Using an air cooling system is a step towards a better, cleaner cup of coffee.”
Ultimately, a shorter cooling time will result in more sweetness – and better results for roasters.
Enjoyed this? Then readour article on when you should upgrade to a new roaster.
Photo credits: Solberg & Hansen
Perfect Daily Grind
Want to read more articles like this?Sign up for our newsletter!
The post Cooling roasted coffee: What roasters need to know appeared first on Perfect Daily Grind.
