Preserving Freshness: A Race Against Time - 25 Magazine: Issue 4
There is now universal acceptance in the coffee community that freshness has a huge impact on flavor and aroma. But what do we mean by freshness and, crucially, how do we measure it?
ANTONY WATSON delves into the findings of a new SCA Handbook which combines scientific research from the laboratory, sensory data from the field, and comment from the industry in Issue 4, 25 Magazine.
Freshness is often cited as a mark of specialty. However, given that the mantra of “freshness” can be subjective from a sensory perspective, it is important to establish a common understanding of the concept. In their seminal publication Espresso Coffee: The Science of Quality, Illy and Viani describe the loss of freshness as a “progressive imbalance in the aroma profile,” while others define freshness as a product which has retained its “original unimpaired qualities.”
Now analysis of member-driven SCA sensory data and scientific efforts towards quantifying freshness conducted at the Zurich University of Applied Science (ZHAW) in collaboration with the SCA have made significant advances in unlocking the key to better understanding the change on coffee quality over time. Their insights are now featured in a newly published SCA Handbook on Coffee Freshness: Understanding & Preserving the Freshness of Coffee. “The findings reveal that if we can further develop the tools to preserve coffee freshness, we can also maximize flavor potential,” notes Peter Giuliano, Chief Research Officer at the SCA. “It’s a win-win situation but the laws of physics show that the odds are heavily stacked against us. This calls for a fresh approach where creativity and ingenuity in the scientific, sensory, and technological fields will help us to achieve our goal.”
The Enemies of Freshness
Firstly, it is worth firing the starting gun on the topic of freshness by identifying its age-old enemies: oxygen, moisture, and temperature – and, of course, time. To a lesser or greater extent, all can affect loss of freshness in different ways. Evidence shows that the oxidation process can dramatically decrease the shelf life of roasted coffee. For example, simply reducing oxygen content to 0.5% in a coffee container can increase shelf life by up to 20 times. Secondly, since water allows for the movement of molecules that further accelerate oxidative reactions, it has been demonstrated that a high moisture environment acts as a catalyst for aging in coffee. Thirdly, as temperature is positively linked to the kinetics of chemical changes and therefore is the main driver of all coffee-staling reactions, we also know that it can speed up the release of carbon dioxide. There is evidence to suggest that a mere 10°C increase in temperature will double the degassing rate. This can mean not just the loss of volatile aroma compounds, but the formation of new aroma compounds that impart unwanted off-flavors in our favorite brew.
Armed with this knowledge, the team of researchers at ZHAW have been working around the clock to help measure the aging process in coffee by investigating coffee freshness and aging from a chemical standpoint. Science Associate at ZHAW’s Institute of Chemistry and Biological Chemistry Dr. Samo Smrke explains: “As we know, one of the first perceivable changes in the loss of freshness is aroma as it fades over time. Not all volatile aromatic compounds, however, behave the same way. Some are highly reactive and are rapidly lost while others are relatively stable and released slowly. Identifiable compounds can be accurately analyzed using various analytical techniques as they become less prevalent in the aroma.
As there are more than 850 detectable volatile aromatic compounds in freshly roasted coffee, the race is now on to develop a practical application that could potentially be used in the roastery or coffee shop environment to detect chemical markers with which to gauge the freshness of a coffee.”
Before a future game-changing test such as this falls into the hands of coffee professionals, training centers also have a vital role to play. Sandra Azevedo, Authorized SCA Trainer and Director of Lisbon’s SCA Premier Training Campus, Academia do Café, says that education is crucial to raising awareness around freshness. “We always impress the importance of coffee freshness on our students, be they roasters or baristas. The coffee’s journey doesn’t end after the roast and so it is crucial that they know how to correctly package or store their coffee at home or in the coffee shop. People will invest in a top- of-the-range grinder or espresso machine but preserving freshness can often be overlooked when it comes to treating coffee correctly. Educating coffee professionals and consumers on freshness means that they have more understanding of how it affects extraction and, ultimately, the changing flavor attributes in the cup.”
Analyzing Off-Gassing
Back in the laboratory, another area of study has focused on the physical process of off-gassing, as a relatively large amount carbon dioxide is released after roasting. Tests show that up to 2% of the weight of freshly roasted coffee is gas trapped inside its porous structure. Taking into account coffee density, roast speed, and degree as well as the environmental conditions in which it is stored, the rate of carbon dioxide release can be analyzed and accurately mapped as a physical marker of freshness. Using the gravimetric method to analyze the amount of gas release, researchers discovered that the faster and darker the roast, the more CO2 is released over time. Meanwhile, a light roast was found to off-gas at a significantly slower rate. As expected, the highest rate of gas release was observed during the first 24 to 48 hours after roast time before tapering off.
The researchers at ZHAW also found an interesting role that off-gassing plays once a freshly roasted coffee is packed. An increased build-up of carbon dioxide in poly-foil valve bags during the first week after roasting partially mitigates oxidation because the release of CO2 forces out the oxygen from the headspace. This means that concentrations of carbon dioxide in a coffee bag typically reach 80%, reducing the oxygen content considerably, and therefore slows down the composition of aroma change over a prolonged period of time. The same is true of single-serve capsules where the protective pressure build-up of gas in the capsule prolongs freshness but also aids crema formation during extraction.
Experiments into freezing coffee found that storing a freshly roasted coffee at sub-zero temperatures actively prolongs shelf life. When comparing a freshly roasted coffee sample stored at elevated temperatures of 35°C, and another at −25°C, the researchers found that freezing coffee significantly slowed down the rate of off-gassing. Although it does not stop the process altogether, a temperature difference of 60°C can reduce this process by up to 35 times. In other words, a coffee with a freshness window of one to four weeks can theoretically be extended from three months to up to a year if stored and cooled correctly.
The Future of Freshness
As our scientific understanding in measuring chemical and physical markers of freshness evolves, so too does our sensory knowledge and understanding of coffee quality. Chahan Yeretzian, Professor of Analytical Chemistry and Diagnostics at ZHAW, believes that new trends in specialty coffee such as cold brew, nitro, soluble – and now even edible coffee – are shaping the way that we define freshness: “Today, I believe that the future of specialty coffee is more about mastering coffee than attributes in the cup. Freshness and consistency are still central concepts, but creativity and fully exploiting the sensory potential of coffee are becoming important to future generations of specialty coffee pioneers.”
The Roasters Guild has also taken up the challenge over recent years. It organized a series of member-driven sensory experiments to investigate, and collect data on, the coffee aging process and how different packaging types have a perceptible influence on quality. One particular test was designed to assess how different resting times after roasting before packing affected the coffee flavor profile. Four resting times (0, 12, 24, and 48 hours) after the roast date were chosen and cupping scores were collected for each sample. The results highlighted that coffees with longer resting times before packing showed a steeper linear decline in quality. The findings also support the ZHAW research team’s work into the effects of off-gassing and how changes in aroma composition can affect coffee chemistry.
Although science can be credited for leading the charge in deepening our understanding of what drives the aging process at a chemical and physical level, the clock on freshness never stops. Some industry commentators argue that the specialty coffee industry has been too slow in developing innovative strategies to combat the enemies of coffee freshness. While we have seen interventions in coffee packaging to extend shelf life – such as pre-flushing with nitrogen or removing the oxygen content by vacuum, to the development of one-way aluminum-lined valve bags – more teamwork is required if we are to truly get a head start on preserving freshness.
Rob Hoos, coffee roasting consultant and Director of Coffee for Nossa Familia Coffee in Portland, US, says that while the coffee community can preserve flavor using a variety of methods such as experimentation with packaging, there is no substitute for offering freshly roasted coffee. From refining business practices to reducing wastage and setting standards for quality and taste, he is confident that coffee professionals everywhere can make a tangible difference by putting shared knowledge into best practice: “Following lean production principles is one of the best things we can do as an industry,” he adds. “Produce what we need only, avoid overages, and package immediately in appropriate packaging to make sure we’re providing a product that we can all be proud of.”
ANTONY WATSON is a coffee roaster and journalist. His new specialty coffee roastery and brew bar – Olisipo Coffee – is due to open in Lisbon, Portugal, soon.
A Fresh Look at the Aging Process
This article highlights just some of the key insights from a newly published handbook that investigates the science behind quantifying freshness and the aging process in coffee, starting at the very moment coffee leaves the roaster. The SCA Handbook on Coffee Freshness: Understanding & Preserving the Freshness of Coffee includes leading research from the Roasters Guild and Zurich University of Applied Sciences (ZHAW). Available to SCA members and the wider coffee community, the handbook is available to buy in print format from the SCA Store, store.sca.coffee.