Why does green coffee storage humidity matter?

Key takeaways

• Green coffee storage humidity is important because inadequate levels can either encourage microbial growth or cause the beans to dry out.
• The ideal bean moisture content is between 11% and 12%.
• The relative humidity level in storage spaces should be kept between 50% and 60% to avoid moisture absorption or drying.

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While it is more stable than roasted coffee, green coffee is susceptible to degradation on its journey from producers to roasters. It’s something producers and exporters need to look out for, because quality is a key consideration in the supply chain, especially within specialty coffee. Therefore, keeping high standards – both in production and storage – is of extreme value.

One of the most important aspects to take into account is your green coffee storage humidity. Too much humidity, or not enough, can impact the quality of your coffee once roasted. Not only is this bad for your product, but it may jeopardise your relationship with commercial partners.

To understand more about why green coffee storage humidity matters, I spoke to a number of producers. They were Saudy Gabriela Laínez Alfaro and Olga Aragón, from Finca El Duende and Finca Olga Erenia in Honduras, respectively. I also spoke to Daniella Boza, from Finca San Antonio Amatepec in El Salvador. Read on for their insights.

What is the ideal level for green coffee storage humidity? 

The ideal level of green coffee storage humidity is between 11% and 12%. 

Producers put a great deal of effort into packaging and storing green coffee within that target range. At this level, green coffee is more stable, meaning it is less susceptible to mould development or, conversely, drying out.

It’s a figure that all specialty coffee producers should aim for. “The humidity at which we leave the coffee is 11%,” Saudy tells me. “Then we store it in hermetic bags, and then in warehouses at room temperature.”

This level is important because excess moisture can significantly impact green coffee. If the conditions are too humid, it can absorb moisture, develop mould, and entirely ruin the coffee. Conversely, if the green coffee storage humidity is too low, it can dry out, leading to unevenness during roasting and woody, flat flavours.

After you’ve dried green coffee to the green coffee storage humidity level, you need to consider how to package it. Most specialty coffee producers use hermetic bags, which create an airtight seal that preserves the green coffee’s current moisture level.

“Once the coffee is dried, with a humidity level between 11 and 11.5%, it is stored in hermetic bags and sacks,” Olga says. “These are supported on wooden ramps separated from both the floor and the wall within a warehouse exclusively for the storage of dried coffee.”

As the green coffee goes into storage facilities and transportation vessels, exporters need to consider the relative humidity (RH) of storage containers. This is the measure of moisture in the air compared to how much moisture the air could absorb. A higher figure means more saturation of water in the air. 

During transit and in roastery storage, the aim is to keep the RH no higher than 60%, ideally in a range between 50% and 60%. These conditions ensure that the green coffee isn’t impacted by external moisture once it is sealed in the packaging.

Maintaining green coffee storage humidity levels is a complicated process. Large-scale storage warehouses, particularly in consuming countries, often use HVAC systems (heating, ventilation, and air conditioning) to achieve it. These:

• Keeping the temperature in an ideal range of 20ºC to 25ºC
• Maintain the relative humidity level in the optimal range of 50% to 60%
• Prevent the development of mould and condensation

Learn more about other considerations for green coffee producers in this video:

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Why does green coffee storage humidity matter?

Green coffee storage humidity matters because the incorrect conditions can spoil an entire lot. If the humidity is too high, green coffee can develop mould, while if it is too low, it can dry out.

Controlling green coffee storage humidity is one of the main priorities for producers and exporters. Otherwise, the coffee’s quality may degrade, impacting its market value, shelf life, and your reputation.

In all of its forms, coffee is hygroscopic. This means that it readily absorbs moisture from its surrounding environment. Therefore, if its storage and transit conditions aren’t completely perfect, it can cause catastrophic damage.

An increase in humidity leads to several issues that are irreversible once they occur. One of the most dangerous is microbial growth. High humidity creates the perfect environment for bacterial and fungal growth in green coffee. If it arrives in this condition with roasters, they may reject the lot entirely, damaging commercial relationships and significantly impacting a producer’s revenue.

High humidity also accelerates oxidation and enzymatic breakdown in green coffee. If this occurs throughout transit and storage, it can dull the coffee’s aromatic compounds and lead to unpleasantly earthy and musty flavour notes once roasted. Beans can also swell, crack, or deteriorate when absorbing too much moisture, affecting their roast consistency and density.

On the other hand, not enough moisture can be just as impactful. If there isn’t enough water content within hermetic sacks or storage containers, the beans can dry out. This also dulls flavour notes, leading to less complex flavours and a lack of acidity.

Apart from all these factors, high humidity also attracts pests and insects. If this happens during transit or storage, the whole lot of green coffee goes to waste, vastly impacting a producer’s income.

3 tips for preserving green coffee storage humidity

#1. Suitable drying and packaging

Packaging, combined with well-thought-out storage practices, plays a frontline role.

It all starts from the farm, as Daniella explains. “We dry the coffee on beds or on a patio until it reaches 11%. Then, we use special bags to keep the coffee fresh and maintain a stable humidity before placing it in the sack.”

Hermetic liners are the gold standard for this purpose. Airtight, multilayer bags made from materials like polyethylene (PE) are commonly used inside jute bags to create a stable environment for green coffee.

These inner liners create a barrier that prevents external moisture from affecting green coffee. They also prevent oxygen and carbon dioxide from interacting with it during storage. Consequently, it reduces the risk of oxidation and microbial growth and preserves the ideal green coffee storage humidity level.

#2. Properly filling hermetic sacks

To make sure that hermetic bags maintain moisture levels, you should properly fill the liner, remove excess air either mechanically or manually, and seal the bags. Any gaps in the seal can allow moisture, oxygen, or pests to enter, risking damage to the green coffee.

#3. Combining hermetic liners with jute bags

It’s also a good idea to use traditional jute sacks alongside hermetic liners. While these don’t directly protect green coffee from moisture, they still play an important role.

As green coffee is handled during transit and delivery, hermetic liners alone may tear or rip open, causing spillages or spoiling the moisture level. With a durable jute bag, exporters and importers can physically handle the green coffee without risking damage.

Evidently, there is a lot to consider when it comes to green coffee storage humidity. Maintaining the ideal level is essential for high-quality specialty coffee, but it requires a lot of work to do so.

MTPak Coffee’s range of PureLock green coffee packaging is a high-performance solution specifically designed to protect green coffee. Our hermetic liners are engineered to safeguard green coffee from environmental factors like moisture, oxygen, and contamination, ensuring freshness, safety, and quality.

They are made from multi-layer PE to provide robust, airtight protection that preserves a suitable moisture level. They are also reusable and recyclable, so you can limit the amount of waste you produce at your roastery. Paired with our custom or stock jute bags, they provide a complete solution for preserving green coffee storage humidity.

Contact the MTPak Coffee team to get a quote on our PureLock green coffee packaging.

FAQ

What is the ideal moisture content for green coffee?

The recommended green coffee moisture level is between 11% and 12%, which maintains flavour quality and stability.

What is the ideal relative humidity level during green coffee storage?

Within storage facilities and warehouses, you should aim for a relative humidity level between 50% and 60%. This prevents the coffee from absorbing moisture, but also from drying out.

How does humidity affect green coffee?

High humidity levels cause green coffee to develop mould, which degrades its quality and can result in entirely spoiled lots. If the humidity is too low, the beans can dry out to produce flat flavour notes.

Image credit: Diana Lucía Grisales Ochoa, Finca La Palma