A guide to managing environmental variables during coffee roasting

Key takeaways

• Ambient temperature, humidity, and airflow all affect coffee roasting.
• Seasonal profile adjustments help maintain consistent flavour throughout the year.
• Log environmental data alongside roast curves to spot hidden patterns.
• Every roastery operates differently, so solutions must be site-specific.

Roasters spend weeks refining roast profiles for particular coffees, and in practice, spend seemingly twice as long trying to consistently achieve the same results.

However, even the most carefully developed roast profiles can change unpredictably if environmental conditions shift. Factors such as ambient temperature, humidity, airflow, and air pressure all influence heat transfer through the machine and the development of chemical reactions, such as first crack, during roasting.

Seasonal shifts, daily weather patterns, and even roastery layout can therefore introduce subtle variations that affect roaster performance. Without accounting for these variables, the same profile that performs perfectly in winter may produce different results during the summer months.

For roasters seeking to maintain consistent flavour profiles and production quality, the skill set to manage environmental conditions is essential.

You may also like our article on designing a compact coffee roastery.

How climate and weather affect coffee roasting

Coffee roasting centres heavily on internal variables, such as managing charge temperature, rate of rise, development time, and end temperature. While these parameters are critical, the environment surrounding the machine will also influence how a roast profile develops – even if all other data points stay the same. 

“Several environmental variables can influence the roasting process, particularly climate, ambient temperature, airflow and humidity,” says Stacy Visser, the Managing Director at The Bean Cartel in Melbourne, Australia. “Understanding how these factors interact with your climate and roasting environment is key to maintaining consistency and control.”

Because roasting relies heavily on controlled heat transfer, even small changes in environmental conditions can alter how quickly heat moves through the drum and into the beans.

Ambient temperature

One of the most obvious environmental factors that many roasters are aware of and account for is ambient temperature. 

“Higher ambient temperatures can speed up roast times, while cooler conditions may slow them down,” Stacy explains.

When the surrounding environment is warmer, heat loss from the roaster is reduced, thereby accelerating the roasting process. Conversely, colder conditions may slow heat transfer and extend roast times.

These changes can influence key stages of roasting, including drying, Maillard reactions, and the timing of first crack. As a result, roasters may need to adjust their profiles to ensure consistent development.

Humidity

At times, humidity is less obvious but also heavily affects roasting behaviour. 

“Higher humidity levels slow the roasting process due to increased moisture content in the air,” Stacy says. 

Variations in moisture content can influence heat transfer efficiency and the rate at which moisture escapes from the beans during roasting, according to Scott Rao’s The Coffee Roaster’s Companion.

In highly humid environments, the drying phase may take longer, which in turn could affect flavour development if profiles aren’t adjusted accordingly.

Airflow & ventilation

Airflow is another important variable. Adequate airflow is necessary to regulate heat distribution within the roaster and remove smoke and chaff generated during roasting.

A coffee roaster’s heating system pulls air from the roastery into the machine. If the room isn’t ventilated properly, a roast can receive unstable airflow, inconsistent draft, slower smoke extraction from the drum, and temperature instability during roasting. 

If airflow is insufficient, unwanted flavours can develop. “Insufficient airflow can result in smoky flavours and dry-tasting coffee,” Stacy adds.

Furthermore, if profiles are developed with insufficient airflow throughout the roastery and airflow is then increased during production roasting, this can lead to inconsistencies in roast development and flavour profiles.

How roasting technology helps manage environmental variables

For many roasters, environmental variability is not an occasional inconvenience but an ever-evolving problem. Roasters must account for a number of external factors when developing profiles and during production roasting.

A profile developed during warm summer months, for example, may produce noticeably different results during colder seasons if tweaks aren’t made.

“Understanding and managing your environmental variables is essential for maintaining roasting consistency, every day,” Stacy says. “Even small changes in ambient conditions can have an impact if you’re not prepared for them.”

To address these challenges, roasting equipment manufacturers have increasingly focused on designing systems that monitor and stabilise roasting conditions. Modern roasting machines are increasingly incorporating sensors and control systems to regulate airflow, temperature, and heat transfer throughout the roasting process.

“Our IMF roaster includes several design features to stabilise environmental variables during roasting,” Stacy explains. “The patented Vortex system makes sure the incoming air reaches the correct temperature before entering the drum, which contributes to consistent heat application and overall roast stability.”

Another component of IMF roasters, known as the Equaliser, regulates the volume of airflow entering the machine. “This helps to evenly distribute heat throughout the drum and reduces temperature fluctuations that can impact roast development,” Stacy adds.

In addition to improving consistency, some roasting systems incorporate heat recirculation technology that captures and reuses residual heat generated during roasting. This not only improves energy efficiency but can also help stabilise roasting conditions by maintaining more consistent heat levels throughout the process.

“The technology built into the IMF roaster provides greater control over airflow and temperature, which helps maintain consistent roasting, no matter the conditions throughout the year,” Stacy says. 

As roasting technology continues to progress, these systems are becoming increasingly valuable tools for roasters seeking repeatability and precision. IMF Roasters will exhibit at MICE2026 at booth G10 from 26 to 28 March, to showcase its latest roasting innovations and explore how technology supports roasters in achieving greater efficiency, consistency, and quality.

Practical guidance for roasters

There are many practical steps roasters can take to actively monitor environmental variables and adjust their workflows to minimise their impact, regardless of the roasting system they use. 

Adjust roast profiles seasonally

One common approach is to recalibrate roast profiles as environmental conditions change. For example, colder temperatures may require slightly higher charge temperatures or adjustments to airflow settings to maintain consistent heat transfer.

Similarly, seasonal changes can also influence how roasters approach development time. In colder environments, increased heat loss may slow roast progression and reduce momentum entering first crack. In these cases, roasters may extend development slightly to ensure sufficient flavour development.

Conversely, warmer conditions often accelerate roast progression and increase heat momentum, which may require shorter development times to prevent over-roasting.

For example, if your normal total roast time for a particular coffee is 9 minutes, with a 1:30 development time in the summer, and a 1:45 development time in the coldest parts of the winter, you may find that the same coffee only meets the cupping standard with a 9:30 total roast time and a 1:45 development time. 

Tracking these adjustments over time allows roasters to build seasonal roasting strategies that help maintain consistency throughout the year.

Log environmental conditions alongside roast data

Recording environmental data alongside roast logs can also provide the insight needed to make proper adjustments throughout the year.

By tracking ambient temperature, humidity, and airflow alongside roast curves, roasters can begin to notice patterns and correlations that may not otherwise be obvious. Over time, this data can help inform profile adjustments and improve long-term roasting consistency.

Initially, this is one of the easiest ways a roaster can start improving quality and consistency across batches if they operate in an environment with fluctuating conditions. 

Optimise roastery layout and ventilation

The physical layout of the roastery can also influence environmental stability. Ventilation systems, airflow management, and HVAC systems can all help regulate ambient conditions within the roasting space.

Depending on the environment you roast in, you may or may not be able to control these variables as well as you’d like. “Where possible, maintaining a stable ambient temperature within the roasting space can make a significant difference,” Stacy says. “This can be achieved through ventilation, fans, heating, or air conditioning.”

Even relatively small improvements in environmental control can help reduce profile variability during roasting.

“Energy efficiency has also become increasingly important. With gas prices rising significantly in recent years, our IMF roasting equipment reuses heat and improves operational efficiency, resulting in cost savings over time,” Stacy adds.

Adapt operational workflows

Some roasteries also adapt their roasting schedules to account for environmental changes. The Bean Cartel, for example, experiences significant seasonal variation in Melbourne’s climate.

“Our roastery is located in Notting Hill, in the south-east suburbs of Melbourne, a city well known for its unpredictable and seasonal weather changes,” Stacy explains. During hotter months, ambient temperatures inside the roastery can increase significantly.

“Higher temperatures can shorten roasting times and affect heat transfer within the drum,” he says. 

To manage this, the team adjusts its production schedule: “We focus on maintaining optimal airflow throughout the space by using multiple fans and starting production earlier in the morning, sometimes as early as 4 am, before temperatures peak.”

Ultimately, there is no universal solution for managing environmental variables. Every roastery operates within its own unique conditions.

“Our Master Roaster, Alan, believes it is important to recognise that every roastery operates in a unique environment,” Stacy says. “Understanding the specific conditions and anticipating potential challenges is key.”

For a long time now, roasters have understood, at least at a basic level, how environmental conditions influence roasting. However, as specialty coffee standards continue to rise and quality control measures for roasteries continue to adapt, the ability to manage these variables has become increasingly important.

With effort put into roastery design, detailed data tracking, and utilising advancements in roasting technology as they become available, roasters can continue to set themselves up for the least amount of variability throughout the year. 

Enjoyed this? Then read our article on how to design a roastery that doubles as a café.

Photo credits: The Bean Cartel

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