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Fall Forecast: 4 Seasonal Environmental Factors That Can Impact Your Coffee Roasting — And How To Handle Them

Fall Forecast: 4 Seasonal Environmental Factors That Can Impact Your Coffee Roasting — And How To Handle Them

If you live in the Northern Hemisphere, you know that saying we had to endure an unseasonably warm summer is an understatement. It wasn’t uncommon to see the temperatures flirting with the 100-degree mark from Fresno to France — and scientists are warning that record strings of concurrent heat waves could become the new normal. 

In fact, the National Oceanic and Atmospheric Association (NOAA) recently released their annual winter outlook for the U.S., calling for warmer-than-average temperatures for the Southwest, drier-than-average conditions across the South, and wetter-than-average conditions in the Midwest and Pacific Northwest. The seasons, they are a-changing!

We all know that environmental conditions greatly impact coffee growing, but these atmospheric changes have us wondering what this means for our coffee beans and how we roast them this fall and winter. Fluctuations in environmental conditions are to be expected, but neglecting or not preparing for these changes can negatively impact your roasting outcome. 

In addition to all the other factors you track to achieve a consistent roast year-round (think charge temp, airflow, and roasting time), it’s important you have at least a basic understanding of how environmental factors play a role.

In this article, we’ll look at four seasonal environmental factors that can influence coffee roasting — temperature, humidity, atmospheric pressure, and altitude — and suggest considerations for each so that you can keep turning out great coffee during the coffee industry’s busiest season.



It’s important to fine-tune your roast profiles as the seasons change. Of course, this will vary depending on where you live and your weather.

Since the biggest defining factor of seasonal change is temperature, it’s helpful to understand how it impacts the ambient temperature of the environment where your roasting equipment is kept. Why? Because ambient temps can influence your charge temperature, green bean temperature, and moisture.

Ambient Temperature and Charge Temperature + Airflow

Ambient temperature can impact roast time — making it longer for the roaster to warm up when the weather is cold and vice versa when it’s warmer. This variable becomes even more important if you roast outdoors or in a warehouse or garage that is not temperature-controlled. 

Cold wind can strip heat energy away from your roaster, and rising temperatures can keep your roaster’s charge temperature (initial temp of your roasting drum before roasting) warmer than you might expect.

All of this can impact the pressure inside your roaster. The differential pressure inside your roaster changes with the weather, yielding a higher negative pressure on warm days and lower negative pressure on colder days.


Adjust roasting temp. Consider starting and ending your roast at a slightly higher temperature to compensate for a lower ambient temperature. Or, if you’re in a warmer climate, start and end your roast at a slightly lower temp.

Use a manometer. Consider placing an air manometer (aka drum-pressure manometer) between the roasting drum and exhaust fan. It reads pressure, not airflow, but it does correlate with airflow. Using the same fan setting daily doesn’t necessarily mean a consistent roast because of weather variables. An air-pressure manometer helps you know how to adjust the fan to provide consistent airflow for every batch. (You’ll need to clean your ducting regularly to make sure your manometer readings remain accurate.)

Ambient Temperature and Green Bean Temperature + Moisture

Beans that are too cold can roast slowly, potentially creating underdeveloped flavors that are at greater risk for baking or stalling. Your stored green beans can also lose moisture in colder, drier temps, making them roast too quickly. 


Bring beans to room temp. If you live in a colder climate, consider taking your green beans out of storage a day before roasting, allowing them to warm to room temperature before roasting. (Experts vary on the ideal temperature recommendations for coffee storage. Some recommend temps as low as 40 degrees Fahrenheit, while others suggest temps between 50 and 70 degrees Fahrenheit.) 

Use less heat to balance out dry beans. You’ll also want to use less heat in your winter roasts due to dry air’s effect on green bean moisture.



Simply put, humidity is the amount of water vapor in the air. This plays a huge role in coffee farming, where green coffee beans are usually harvested and dried until they have a moisture content of around 12 percent — considered by many to be the optimal moisture level for producing the best flavor when roasted.

But did you know that humidity can impact your roasting process? In particular, it influences your roasting airflow in a couple of different ways:

  1. Heat is transferred more efficiently if the hot air inside the roasting chamber has a high moisture content. When this happens, your roast may progress more quickly. (This can also cause your beans to lose moisture more quickly.)

  2. If your roaster isn’t heated up, then humid air flowing into the roaster will compete with your green beans for heat energy, leading to a slower roast.

Roasting legend Scott Rao echoes these points in his book, The Coffee Roasters Companion, noting that humidity in the roasting air increases heat transfer efficiency, causing the bean to lose moisture quickly. 


More Humid Than Usual

Use lower charge temp. Your roast can quickly run out of hand if the weather is both humid and warm. So, you might want to use a lower charge temperature and lower heat around First Crack.

Less Humid Than Usual

Keep an eye on your roast! If you’re experiencing lower humidity conditions than you’re used to, just know this will make your roasts quicker — so be sure to watch them. With the same settings and batch size, it’s possible to reach First Crack a good minute or so sooner than you might expect.

If you’re expecting big temperature swings this fall and winter and humidity levels higher or lower than usual, you might consider investing in either a humidifier or dehumidifier to help regulate the ambient conditions of your roasting area, which can also help to stabilize your green beans’ moisture content.

Another Word About Those Green Beans

While this article focuses on roasting, we can’t overlook adding a quick note about the role humidity plays in green bean storage

If a storage facility is too humid or dry, the beans respectively gain or lose moisture, impacting their flavor. So, where you live — and whether or not you have climate-controlled storage — might impact how long you store your green beans and where you get them from. 

Most experts can’t seem to agree on a specific relative humidity percentage for optimal green bean storage, though recommendations usually fall between 50 and 70 percent. However, there’s a consensus that stable conditions, including good ventilation and insulation, go a long way. 


Looking to better control or understand your green beans’ moisture content? Pick up a moisture reader or density meter.


Atmospheric Pressure

You might know that atmospheric (or barometric) pressure is important, but do you know exactly what it is? In simple terms, it is the pressure of the air that presses against everything it touches. It is the force exerted on a surface by the air above it as gravity pulls it to Earth. Due to gravitational pull, atmospheric pressure is typically higher in lower altitudes and lower in higher altitudes. 

Along with altitude, weather systems can also impact atmospheric pressure. For example, hurricanes are low-pressure storms, while high-pressure systems bring wind storms and tornadoes. 

So, what does this matter to our coffee roasting? It all comes down to its impact on airflow.

Impact on Airflow

If the ambient air is more dense than usual due to higher atmospheric pressure (which also brings higher moisture/humidity), this will provide more resistance to your roaster’s fan, and your airflow will be lower. The reverse, then, will be true if a low-pressure weather system settles into your geographic area.

Of course, how much this weather variable affects your airflow would ultimately depend on the extent of your airflow. If you typically roast with a low airflow, your end result won’t be affected as much.


As an experiment, pay attention to your local daily forecast for barometric pressure readings. How will you know what the atmospheric pressure is on any given day?’s daily forecast includes this data point, and a barometric pressure reading (aka atmospheric pressure) is almost always included in home weather stations



Once again, much has been studied and written about how altitude impacts coffee farming. Let’s consider for a moment how altitude impacts coffee roasting. 

Air contains less oxygen and moisture at higher altitudes, and it’s also colder. Because of this, you need to increase your roasting temperatures, as more heat is needed to achieve a good roasting curve. The converse is true for lower altitudes, where it’s usually hotter and more humid.

If you’re used to roasting in low-altitude climates and are roasting at a higher altitude, you can get coffee that’s a little raw because you’re used to using a lower temperature. And, if you switch from roasting at a higher to a lower altitude, you risk burning the coffee since you’re used to dialing in higher roasting temps. 

The question is: Which altitudes are better for roasting? Many roasters believe there’s a greater advantage in roasting at higher altitudes because of the amount of better control a roaster can have on the roast profile. It’s also believed that lower-altitude climates are normally hotter and more humid, which can negatively affect roasting time. 

Like many factors when it comes to coffee roasting, everyone has an opinion about what is best. If you live in a particularly high or low altitude, we’d be curious to hear your take, along with how this impacts your roasting.


You may need to increase your roasting temps if you live at a higher altitude.

You may need to decrease your roasting temps if you live at a lower altitude.

No Matter Which Climate, We’ve Got the Right Roaster

Now that you’ve got a better handle on how environmental factors impact your coffee roasting, know that we’re here to help match you to just the right roaster for your roasting climate.

Contact us for a chat. You can also connect with Sales at 800-999-1600

We’ve always got a rotating selection of used and new equipment, and we take time to understand what you’re looking for to keep your roastery running. We can also advise on your roastery plans and logistics in light of pandemic supply chain disruptions. 

And, if you need financing support, check out our Roaster’s Choice Lending Program, where our private network of the nation’s top lenders with your own designated point of contact will help you find the best financing deals available. To get a sense of the monthly payment amount and start the financing application process, just find a roaster you’re interested in (with a value of $2,000 or more) and click the green “Finance It” box for details. 

Let’s help you build the coffee roastery of your dreams — and with a roaster that’s right for you.


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