July 23, 2018

How Oxygen Damages Green Coffee Quality – & What You Can Do


We all know that oxygen ages roasted and ground coffee – but it’s not just once coffee has left the roastery that it’s vulnerable. Oxidation in green beans can also be a huge issue, one that producers, traders, and roasters alike should be concerned about.

Green bean oxygenation can reduce coffee shelf life, aroma, flavor, and ultimately prices. And the longer the journey from drying beds/patios to roaster, the greater the likelihood of significant damage. But the good news is that you can take steps to dramatically reduce this.

To learn more about this, I reached out to three specialists: Prof. Flávio Borém, a professor at the Federal University of Lavras (UFLA) in Minas Gerais, Brazil; Juan Vargas, Quality Manager at Fazendas Klem in Matas de Minas, Brazil; and Claudio Francisco, Sales Representative and Coffee Project Coordinator at Videplast, a packaging manufacturer. Here’s what I discovered.

Lee este artículo en español Cómo Prevenir los Daños por el Oxígeno en el Café Verde

Green coffee beans inside 60kg Videplast high-barrier bag. Credit: SanCoffee

Oxygen: Vital But Dangerous

Oxygen affects everything; in fact, Claudio Francisco of Videplast tells me that even we humans age because of oxidation.

And just like humans, coffee needs oxygen: the key lies in controlling how much it has access to.

Professor Borém conducted research at UFLA in partnership with Videplast to determine the impact of different kinds of green coffee packaging on quality. He explains that oxygen levels were critical for this.

You see, we need to remember that coffee beans are actually seeds. As seeds, they are a living, organic object – and as a living object, they breathe. The only difference is that they do so at a cellular level.

Prof. Borém explains, “The seed is placed in storage practically dry, with 11% water – a very small number, if compared with other living beings. This phenomenon is called anhydrobiosis, life with little water. With this, [the coffee] can maintain a low metabolic activity.

“In order to avoid its death, it needs to keep breathing, so oxygen ends up being an important gas for the preservation of the coffee bean’s life.”

But too much oxygen, and the flavors and aromas will fade. “So, what was our strategy during coffee storage to preserve quality for longer?” The professor asks. “Reducing the amount of oxygen to the specific level at which the coffee can remain living but with the minimum possible oxidation.”

You might also like: Roaster Guide: Why Is Green Bean Moisture Content Important?

Green coffee stored in 1,500-kilo high-barrier plastic big bags with Videplast liner.

Why Is Oxygen So Damaging?

We’ve already mentioned that coffee seeds use oxygen to breathe. But in doing so, they change – in minuscule, almost invisible ways that, over time, can have a dramatic impact on quality.

As the cells breathe, they generate energy. This happens as nutrients (especially glucose molecules) are broken down into water; carbon dioxide; and ATP, which stores and transfers energy.

Let’s put this under the microscope, metaphorically speaking: Prof. Borém explains that “as long as the coffee bean breaks down these reserves – oxidizes these reserves – it decreases or changes the chemical composition of coffee and, therefore, changes its taste and smell.”

And coffee is particularly prone to a changing flavor profile. “In the specific case of coffee,” he continues, “in addition to these reactions, the external part of the coffee cell has a lot of oil… and the oils rapidly become rancidified in the presence of oxygen.”

All this can lead to a decreasing quality, visible in the cupping score used to indicate quality, as well as moldy and premature “past-crop” flavors.

High-barrier bags are placed inside jute bags for storing green coffee. Credit: Fazendas Klem

Losing 10 Points in 1 Year: Oxygen & Cup Quality

Claudio says, “From the time [coffee] oxidizes, it starts to lose cup points… We can start to perceive the sensory changes after six months, according to the study. Until the third month, [the sensory profile] stays the same, but the chemical aspect starts to change earlier.”

He’s seen coffee samples that, when stored in traditional bags, have lost an entire point every month after the sixth month.

In his research, Prof. Borém measured the decreasing cup quality of pulped natural coffee stored in a variety of different coffee bags over 12 months. All samples started with approximately 84 points; remember, anything 90+ is exceptional, 80+ is specialty, and less than 80 is commodity-grade.

Here are his results:

Evaluation of Packages and Storage Methods for Specialty Coffees

Evaluation of Packages and Storage Methods for Specialty Coffees, Prof. Flávio Meira Borém

Paper bags saw an incredible loss of 10 points over just 12 months: a devastating fall in quality for producers, traders, and roasters. Low-barrier paper bags and jute bags also saw a dramatic fall of around seven points.

On the other hand, high-barrier packaging resulted in less than one lost point over the year, while vacuum-packed coffee saw quality diminish by slightly over 1.5 points.

So, what is high-barrier packaging? Prof. Borém defines it as “a pack with different compositions and structures which are capable of preventing gas and water exchanges between the inside and the atmosphere… It’s packaging with high impermeability.”

In other words, it’s able to block the diffusion of gas and water from the external environment into the bag, creating an almost inert atmosphere. In this way, the coffee’s quality can be mostly preserved. The beans continue to breathe until the rate of oxygen is too low, and the rate of carbon dioxide too high, to allow deterioration.

A stack of 1,500kg big bags, complete with Videplast liners, being transported in a warehouse. Credit: Bourbon

How To Protect Green Coffee From Oxygen

Juan Vargas of Fazendas Klem agreed to share his insights into practical ways to protect green coffee from oxidation. We’ve already seen the importance of selecting the right packaging, but a producer’s work doesn’t stop there.

After all, knowing the best way to protect those green beans is crucial. As Juan says, “What normally happens? The producer processes the coffee and leaves it in the warehouse, and they don’t know when they are going to sell it. So, if you leave it exposed during this time, you will lose a lot of money and all your hard work. Perhaps, you will lose your profit margin.”

His first recommendation is to be aware of the warehouse conditions. “Even if the protection barrier [of the packaging] is good, with plastic and everything else, there will be always [external] influences inside the plastic bag,” he stresses. “If the surrounding area is very wet, it will affect the raw product.”

He also points out the need to use the packaging correctly. Once the coffee has been weighed, he says, it’s time to tie the bag. However, it’s important to remove as much oxygen as possible from the bag and ensure that the plastic is smooth and completely pulled up. Air pockets inside the bag are bad news.

It takes longer to do this, he tells me, but if done well the effort pays off. It results in better-quality coffee (and can result in more efficient storage inside the container).

A container of coffee stored in palletized high-barrier Videplast bags, in addition to external stretch plastic protection. Credit: Fazenda Primavera

We want the coffee we sell, buy, and roast to be just as good as the day it left the drying beds. But in order to achieve this, we need to pay attention to every detail. Limiting oxidation is vital for coffee quality, freshness, and pricing.

So, follow the tips above. Pay attention to your warehouse conditions. And make sure you store and transport your coffee in good packaging.

Enjoyed this? Check out: Roaster Guide: Why Is Green Bean Moisture Content Important?

All interviews conducted in Portuguese and translated by the author.

Please note: This article has been sponsored by Videplast.

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