December 21, 2020

How Does Green Coffee Become Contaminated?


When storing or transporting green coffee, contamination is always a risk. Whether it’s through oxygen, moisture, or a range of other sources, improper storage and packaging can lead to green coffee becoming contaminated. In turn, this can cause it to decrease in quality, or even become unsafe to drink.

To learn more about how green coffee gets contaminated, how dangerous this might be, and how to protect against contamination risks, we spoke with Stephane Cuchet, the co-owner of Soluagro, a company that provides packaging solutions for agribusinesses in Guatemala. Read on to find out what he said.

You might also like How Can Coffee Traders Raise Brand Awareness?

Producers sealing green coffee in Ecotact’s hermetic high-barrier bags

What Is Contamination?

According to the Cambridge Dictionary, contamination can be defined as “the process of making something dirty or poisonous, or the state of containing unwanted or dangerous substances”.

However, in reference to coffee, Stephane says: “When we talk about contamination, we refer to all the external factors that might negatively influence coffee. 

“This could be mold, moisture, external odours or aromas, and any factor outside of the packaging that might damage the coffee in any way,” he says. “Contamination is all of these factors… everything that can be detrimental to the coffee’s quality when it is in storage, in transit, or anywhere else in the supply chain.”

Let’s look at some of the ways that green coffee gets contaminated.

A producer transferring green coffee from one bag to another

How Can Green Coffee Get Contaminated?

Stephane says that coffee is “what we call a hygroscopic product”. This means that it is particularly prone to absorbing moisture from the air, and with it, any contaminants (such as odours or chemicals) that may be present.

As such, if your green coffee is not packaged appropriately, it can be exposed to external contaminants. If it is, it will likely absorb undesirable odours, flavours, and other compounds, which can cause cup quality to decrease and possibly even make the beans unsafe. 

Stephane tells me that when working with producers in Guatemala, he offers 9-layered hermetic bags from Ecotact as part of his company’s catalogue.

“Coffee is really like a sponge,” Stephane adds. “If you put something that smells very strong next to it, it can definitely absorb it… that’s what you want to avoid.”

I spoke to Stephane to learn more about the different contaminants that can affect the flavour, quality, and safety of your green coffee. Here are a few.

Mold Growth

Mold is one of the most common contaminants of most food products, and green coffee is no exception. 

Mold is caused by fungi such as Aspergillus and Penicillium. It forms naturally in improperly stored food products, often in humid environments. Studies conducted on green coffee in coffee-producing countries all around the world show that these two species of fungus are particularly common natural contaminants.

Essentially, if green coffee is not properly packed and exposed to moisture (whether that’s in the air or otherwise) mold will develop. This can ruin the coffee’s quality, while also causing it to become potentially harmful to humans.

When mold grows in coffee, it has a characteristic smell that can easily be confirmed by examining the affected beans.

Green coffee stored in a warehouse using hermetic Ecotact bags

Animal Contamination

Stephane tells me that animal contamination is another major problem when storing green coffee. While there is always the possibility that larger animals can damage the coffee through physical contact, Stephane actually tells me that rodents are a major cause for concern.

“It depends which kind of warehouse we’re talking about,” he says. “But sometimes you have mice. I would say mice are one of the worst types of contamination.”

He says that mouse urine in particular can be an issue if coffee is not stored properly, as its undesirable odours can be absorbed by the green coffee.

Oil Products

Oil products are also a significant contamination risk for green coffee, as any absorption of non-edible or industrial oils can be incredibly dangerous for the consumer. 

“Warehouses are places with plenty of external factors,” Stephane says. “You can have oils coming from the forklift, diesel or gasoline… and you also have vehicle fumes, [which are dangerous].”

Stephane says that when any oils are stored near green coffee storage facilities or warehouses, leakage is always a potential risk. This can be incredibly hazardous if coffee is not properly stored. Additionally, any aromas, gases, or fumes given off by oil products can also be absorbed.

Green coffee on pallets, ready for shipping

Chemical Contamination

Just as oils are a risk, so too are other chemicals that may come into contact with the areas where green coffee is stored.

Stephane says: “People [sometimes] store pesticides and agricultural inputs [near coffee], and even though these things shouldn’t necessarily be in direct contact with coffee, they just store it one next to the other.

“You definitely need some kind of barrier to prevent [contamination in this case].”

Fertilisers and other agricultural inputs could be incredibly dangerous if they contaminate green coffee that is then roasted and brewed.

However, beyond this, there is another chemical risk to consider when storing green coffee: hydrocarbon contamination.

According to an FAO report by Bart Slob, hydrocarbon contamination “is usually caused by jute coffee bags”.

The report says: “This is because of the ‘batching oil’ used to soften the jute fibres before spinning. There have been instances of contaminated oil being used (old engine oil for example).”

Stephane adds: “Not all the natural fibers [in jute bags] are food-grade, which is when materials are suitable for prolonged contact with beans, grains, or any other food product. 

“Some bag materials and fibres are not food grade because of the type of oil used to treat them, many of which are not edible.” However, he notes that Ecotact’s 9-layered hermetic coffee bags are 100% hydrocarbon free.

Oxygen & Cup Quality

Technically, oxygen can be considered a contaminant for green coffee. Studies have shown that exposure to oxygen causes oxidation, which can affect the coffee’s flavour and ultimately decrease cup quality.

One study states: “When green coffee is stored for a prolonged time the coffee quality decreases distinctively. Apart from well-known ‘off-notes’ that arise from undesired oxidations of lipids, a typical ‘flattening’ of the cup quality is detectable.”

Stephane says that when coffee is in direct content with oxygen, “a process called oxidation takes place… this is what makes a coffee taste ‘old’”.

Green coffee in storage

How Do You Avoid Contamination In Green Coffee?

Since we have listed many different types of contamination risks for green coffee, let’s now look at how to avoid them.

Initially, following some basic practices is a great first step, as follows:

  • Make sure your warehouse is kept dry and clean
  • Use pallets to store and transport coffee
  • Avoid storing fertilisers, pesticides, or other chemicals next to green coffee
  • Monitor pest incidence in the warehouse

However, if you want to prevent all these contamination risks at once, Stephane has one key tip: use good quality packaging. “This is where Ecotact bags have a major role to play,” he says. 

“These bags have a hermetic 9-layer barrier that protects against any external factors that might contaminate the coffee. This is where it guarantees the protection of the bean inside; not only will it keep its freshness, it will also keep its aroma, taste, and all the other attributes that improve the characteristics of the coffee.”

Another advantage of the Ecotact bags, according to Stephane, is that they are “totally reusable… you can empty [the bags] and reuse them again”. Additionally, the bags are fully recyclable, as he tells me Ecotact provides a number of packaging solutions that focus on reducing the environmental impact of the supply chain.

“With Ecotact’s 9-layered polyethylene bags, you can guarantee the shelf life of coffee for over a year, and [make sure] the taste of the beans remains fresh,” Stephane says.

“We have conducted coffee cupping tests with coffee that has been stored for about a year, and the taste is still not woody, nor does it taste of past crop.”

The hydrocarbon-free bags also provide excellent transparency, and are able to tolerate temperatures ranging from -30°C to 90°C. Additionally, the high-barrier packaging means the beans do not come into contact with any external contaminants, including water, oils, chemicals and oxygen.

A variety of Ecotact bags in different shapes and sizes

As there are many factors which can contaminate green coffee and cause it to lose quality, it’s incredibly important that producers take the right precautions to protect it during storage or transport.

Contamination doesn’t just mean a decrease in quality, either. Exposure to one of any number of undesirable external agents can be potentially hazardous for the end product.

However, by correctly storing and protecting your green coffee, you can minimise the chances of this occurring, and ensure that quality is preserved in the warehouse and beyond.

Enjoyed this? You might also like How To Protect Green Coffee From Excessive Water Activity

Photo credits: ASSY, Caelen Cockrum, Soluagro, Ana Valencia, Ecotact

Please note: Ecotact are a sponsor of Perfect Daily Grind.

Perfect Daily Grind

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