Measuring the freshness of roasted coffee stored in packaging: A quantitative study

Ben James
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October 20, 2021
packaging research journal

As a member of the SCA board of directors, Professor Chahan Yeretzian was keen to apply his scientific background to evaluating the freshness of coffee – a cornerstone of the specialty coffee sector. His research culminated in the publication of a landmark study that used quantitative indices to measure freshness across a range of packaging materials.


Ever since the emergence of a “third wave” in coffee, freshness has been a pillar of the specialty coffee industry. Not only is it used by roasters and coffee shops to entice customers, it has become a byword for quality.

However, despite its ubiquity, relatively little in the way of an objective and quantitative measure of freshness exists. While certified Q graders can use their experience to make assessments on the cupping table, it tends to lack the scientific approach necessary for a truly objective interpretation.

When Professor Chahan Yeretzian PhD, MBA, joined the Specialty Coffee Association’s board of directors, he decided that introducing a quantitative measure to the concept of coffee freshness should be a priority.

So, together with scientists at the Coffee Excellence Center in Zürich, he set out to identify objective ways of assessing it, before applying the methods to measure the freshness of coffee stored in a selection of packaging materials.

“Freshness is an important attribute of specialty coffee,” Chahan tells me. “The way I define it is the state of a product at time zero – it’s like a watch that starts the moment the coffee leaves the roaster.

“For us, the fundamental motivation was to identify common attributes that could be used to provide a quantitative measure of freshness over time.”

The two attributes they identified were, first, the amount of carbon dioxide (CO2) entrapped in the porous structure of the roasted coffee that was subsequently released (measured as degassing); and second, as selected ratios of two volatile organic compounds (VOCs) found in the packaging’s headspace that contribute to coffee’s aroma. Both were identified as key indicators of freshness.

“When you find two compounds that are chemically related, with one that degrades over time and the other that develops over time, you have a ratio that offers a robust measure of freshness,” Chahan says.

“You can then combine this with a measure of CO2 based on the variety, roast degree, and roast profile of the coffee. It’s particularly important to calibrate it with the roast degree, because darker roasts usually have more CO2 than lighter roasts.”

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chahan yeretzian carrying out experiments
Chahan observed changes in the coffee over the course of several months

Packaging solutions

With quantitative measures in place, Chahan and his team could now effectively measure the impact that different packaging materials and storage conditions had on the freshness of coffee.

For this, they chose four different types: plastic, aluminium of two different thicknesses, and paper without a degassing valve. Their choices, Chahan says, were based on the assumption that specialty coffee is typically consumed within six weeks of roasting.

“The question we asked ourselves was, ‘If specialty coffee is consumed relatively soon after packaging, do we need these complex, multilayered aluminium materials, which aren’t that sustainable,” he explains, “or would paper packaging without a degassing valve do the same job?’

“So we used the same coffee (an arabica whole bean from Guatemala) across all four packaging solutions and the conclusion was obvious – even after just ten days.”

According to their findings, the freshness for the coffee stored in paper and – to a slightly lesser extent – plastic packaging, degraded significantly quicker than the coffee in aluminium packaging. Minute differences were detected between the two types of aluminium, with the thicker packaging providing marginally better results.

“The two aluminium bags were on a different level,” Chahan says. “In terms of offering a barrier against oxygen, the only material that can compete is glass – but glass just isn’t practical.

“Clearly, the goal is to have sustainable packaging that doesn’t compromise the coffee’s quality. But often, people will talk about the sustainability of the packaging without questioning whether it actually offers proper protection.

“If we accept that the primary role of packaging is to preserve the coffee’s quality, then aluminium is the best option.”

roasted coffee in jars
One of the challenges was how to maintain consistency for the duration of the study

Practical steps for roasters

Despite an obvious conclusion in favour of aluminium packaging, Chahan’s experiments were not without their challenges. He tells me that one of the major questions was how to maintain consistency over the weeks and months of analysis.

“When you taste something for the first time and then again four months later, you have to be able to compare them in absolute terms,” he says. “For this you need very stable instruments and it’s one of the reasons we introduced ratios: sometimes, because of some issue in the machine, the values might change, but the ratio was a robust solution.”

Naturally, without the proper equipment it can be difficult for roasters to carry out similar tests of freshness for their own coffee. However, there are a few simple ways of prolonging shelf life and minimising the risk of oxidation.

Chahan says that the period at which the most damage is done typically occurs between roasting and packaging.

“If coffee is an airtight packaging, it creates its own protective atmosphere – and that’s not a bad thing. But moving coffee from one vessel to another basically loses its blanket of CO2. So don’t move it and let it develop a protective blanket.

“I would also say that if grinding for capsules, it is best to do it in an inert atmosphere and package it immediately. People often say that ground coffee is not the same quality as whole bean. But if you do it like this, then it can be very fresh.”

Temperature is also important. It’s estimated that an increase in temperature of just 10°C will accelerate ageing by a factor of two. Therefore, keeping coffee in a stable environment will help slow down the process of degradation.

But what about wholesale coffee, which can often spend months sitting on a grocery store shelf?

“There are two things at play when thinking about freshness,” Chahan says. “You don’t want to lose aroma, but you also need the coffee to degas a little. It’s about finding the right balance for each.

“The freshest coffee possible is not actually the goal. Coffee needs time to release some of its CO2 after roasting, otherwise it is very aggressive and unbalanced. Anything consumed within six weeks we call the ‘specialty age’, and anything between six weeks and several months we call the ‘golden age’.

“While there are people who will call this later phase ‘old coffee’, it’s actually the point at which the characteristics are more balanced, harmonious, and stable. If you have the correct packaging and storage conditions, then it’s almost like a coffee’s second life.”

black sustainable coffee bag
Finding high-barrier coffee packaging is key to preserving freshness

Freshness is one of the central tenets of specialty coffee and preserving it is of the utmost importance. While much of what roasters between the roasting and packaging stage can affect freshness, packaging also has a significant impact.

To prolong the shelf life of roasted coffee and ensure it arrives at the consumer in peak condition, high-barrier pouches with degassing valves are advised.

At MTPak Coffee, we have a range of multilayer coffee bags that will keep out oxygen, while providing full sustainability. We also offer recyclable degassing valves that can be fitted to the bags either before or after manufacture.

For information on our sustainable coffee bags, contact our team.

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Measuring the freshness of roasted coffee stored in packaging: A quantitative study

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