Many coffee enthusiasts often ask themselves, "How long does coffee remain truly fresh?" and "Where is the best place to store it?" In this article, the author, Samo Smrke, takes readers on a scientific journey through the galaxy of "Coffee Freshness" and answers the most common questions. The text has been translated and prepared based on Samo Smrke's article.
The concept of freshness lies at the core of the specialty coffee phenomenon since its inception. It is one of the key parameters that receives attention.
Freshness of coffee is a matter of interest not only for specialty coffee but also for commercial purposes. This is evident from the latest trends in the coffee industry, which seek ways to achieve better coffee taste.
Researchers from the Coffee Excellence Center at the Zurich University of Applied Sciences have been studying the influence of coffee freshness on taste for the past ten years.
What is the freshness of roasted coffee?
For coffee to be fresh means to have as many original qualities as possible that have not been affected by external influences. This is especially important when we talk about the freshness of roasted coffee. The thing is, roasting not only creates the aroma of coffee and makes the beans extractive, but it also deprives the coffee of stability. It is after roasting that oxygen penetrates the coffee beans, allowing the aroma to dissipate. As a result, in order to understand what coffee freshness is, we must first understand how and why it is lost.
The four most important factors that affect coffee aging:
-
Space
Freshly roasted coffee beans are saturated with volatile aromatic molecules. Under the influence of physicochemical forces, these molecules will strive to escape into any open space around the coffee beans.
-
Oxygen
When coffee beans come into contact with oxygen, some of the delicate aromatic components degrade. This change is insignificant because more often the aroma simply dissipates into the open space around the beans. However, another reaction, the oxidation of coffee oils, leaves very unpleasant rancid notes in the taste.
-
Temperature
Both of the processes mentioned above, aroma diffusion and oxidation, depend on temperature. It causes molecules to move, and the higher it is, the faster this happens.
When they move quickly, the aroma escapes from the beans faster, and the damage from oxygen becomes greater. Theoretically, if we could cool coffee to absolute zero, its freshness could be preserved indefinitely.
-
Time
Freshness is not lost instantaneously—each process takes time.
These four factors help us understand not only the processes underlying coffee freshness but also how sensitive this product is. In addition to what has already been mentioned, humidity or bright light can also influence coffee freshness. It has been found that high humidity in ground coffee increases the intensity of aroma loss.
The most essential attribute of coffee is, of course, its taste. But when we look at the bigger picture, it is not the only thing we need to pay attention to. Coffee freshness is composed of many components, and when we talk about freshness, we can distinguish two types: chemical and physical.
Chemical freshness is related to changes in coffee aroma, while physical freshness is associated with a phenomenon known as degassing.
Chemical freshness of coffee
We study the composition of coffee aroma using a gas chromatograph/mass spectrometer—two devices in one. The first separates the different molecules that make up the aroma, while the second determines their mass. This way, we know what the aroma is made of.
Based on these measurements, we can identify freshness indicators. They represent the ratios between different aromatic compounds. These indicators are extremely useful in testing the influence of various parameters on coffee aroma, such as evaluating the impact of different packaging materials or capsules, temperature, or time after opening the packaging.
To see how the scientific approach helps us understand why the taste of coffee changes over time, let's consider four completely different aromatic components and trace their evolution over time:
-
Methanethiol (organoleptic properties: garlic, cheese, cabbage, rotten eggs)
-
Propanal (organoleptic properties: ethereal, wine-like, earthy, whiskey, cocoa)
-
2,3-Butanedione (organoleptic properties: oily, buttery, sweet, vanilla)
-
Methylpyrazine (organoleptic properties: nutty, chocolatey, peanut, green)
Each aromatic compound possesses numerous sensory descriptors that resemble various smells. The differences arise from perceiving their aroma in varying quantities or under different conditions. Considering that these four aromas develop differently within coffee beans during storage and that their ratio to each other changes significantly over time, we can predict that the aroma of coffee will also change over time.
If we take as a starting point 100% of each aromatic compound inside the coffee bean immediately after roasting, after 2 weeks, we will be left with only 20% of methanethiol, approximately 60% of butanedione and propanal, and 80% of methylpyrazine.
Imagine that coffee contains about 40-50 key aromas, each behaving differently. Furthermore, the same compound can have both positive and negative odors, which only change depending on its concentration. For example, beta-damascenone smells unpleasant and smoky at high concentrations, but has a pleasant floral scent at low concentrations. It becomes evident that we are dealing with a very complex situation when it comes to the development of coffee aroma over time.
Each coffee variety will have its own peak of optimal perception. The extraction method also plays a role—if we use the same coffee for espresso and filtered coffee, these peaks will differ.
Physical freshness of coffee
Degassing is a process that occurs during the storage of freshly roasted coffee. During roasting, a large amount of gas, mainly carbon dioxide, is generated, which remains "trapped" in the beans and gradually escapes. We are aware of this phenomenon because if coffee is stored for a long time in sealed bags, we can observe them swelling. Degassing is the reason for the presence of special valves in coffee packaging.
We refer to this freshness as physical because the processes influencing it are related to the physics of coffee and the surrounding technologies. Degassing can also be measured using instruments that measure physical properties. We can place the beans in a sealed container and measure the pressure changes caused by degassing, or we can place the coffee on highly accurate scales and measure the weight loss caused by degassing.
Interestingly, the weight of gas in roasted coffee constitutes a significant portion. Approximately 1% of the weight of freshly roasted coffee is gas, which will dissipate over time (it takes about 1-2 months for complete degassing). The degree and duration of degassing primarily depend on the roasting profile—darker and faster roasts typically produce more gas and release it more rapidly. The growing region, variety, and processing method of coffee can also have a slight influence on degassing.
We can all observe the consequences of trapped gas in roasted beans, whether it's the crema in espresso or the blooming during pour-over brewing. Some of them may complicate matters, such as blooming or the need for more intricate packaging, but for espresso crema, they are essential.
The relationship between degassing and coffee age is most visibly demonstrated in the amount of crema produced during espresso extraction. This can be demonstrated by preparing espresso from the same coffee, roasted using the same profile, brewed with identical parameters but of different ages. The amount of crema obtained will directly depend on the age of the coffee.
Changes in crema density depending on the age of the bean
Practical tips for preserving coffee freshness
Due to the elusive nature of aroma origin, it is challenging to find a universal recipe for preserving coffee freshness. Based on numerous studies conducted at the Coffee Excellence Center (some of which are presented in the SCA Coffee Freshness Handbook), we can draw certain conclusions and provide recommendations for maintaining optimal freshness of your coffee.
Roasting
When coffee is roasted quickly or darkly, the beans contain more gas. During rapid roasting, the internal gas pressure on the beans becomes high, increasing the risk of oil exudation on the surface of the bean during degassing. If you want to avoid rancid notes in the taste, it is important to prevent oil from coming to the surface of the roasted bean.
Packaging
The best packaging simultaneously prevents the escape of aroma, prevents oxygen from entering, and allows carbon dioxide to escape from the package through a one-way valve.
Ideally, the best protection against oxidation of the beans is achieved when the packaging is done in an oxygen-free environment, such as nitrogen or vacuum. The extent to which the packaging should protect the beans depends on the expected storage period from the time of packaging until the package is opened and the susceptibility of the beans to aging. If you plan to consume the coffee within a week, a non-valve paper packaging may be a good option. However, if the coffee is intended to be stored for several months, the packaging should be equipped with a laminated aluminum layer and a one-way valve, and it should be nitrogen-flushed.
Storage
Temperature is the most critical parameter for storage. It is best to store coffee in a space where the temperature remains at room level. It is known that with every 10°C increase in temperature, the rate of aroma loss roughly doubles. At certain temperatures, oxidation processes can accelerate even more. Exposure of the beans to high temperatures (above 50°C) even for a short period can irreversibly damage the aroma.
Extraction
Keep in mind that due to the degassing process, coffee becomes less stable with age. You should adjust the extraction parameters considering the aging of the beans.
Freezing
A good way to preserve coffee freshness is to freeze the beans. Roasted coffee contains very little moisture, so there is no risk of the coffee being affected by ice formation during freezing. Storing coffee in the freezer can extend its freshness by approximately ten times. This means that if coffee is considered fresh for about a month, storing it in the freezer can extend its freshness to around a year.
When freezing roasted coffee, certain precautions should be taken:
-
Store the coffee in a well-sealed package to prevent moisture and odors from other items in the freezer from affecting the coffee beans.
-
After removing the coffee beans from the freezer, always allow them to reach room temperature. If the packaging is opened while the beans are still cold inside, moisture will condense on them, accelerating the aging process. We recommend leaving a 250-gram package at room temperature for approximately one hour, and a 500-gram package for at least two hours. Beans conduct heat poorly and require sufficient time to warm up. Even if the packaging has warmed up on the outside, the beans inside may still be cold.
Time
We cannot stop time. Enjoy your coffee at its best—when it is fresh! But how long does freshness last? It all depends on the brewing method you prefer, the roast style, coffee variety, and personal preferences. There are too many variables in this equation to have a definitive answer.
For example, cupping should be done within 24 hours of roasting. On the other hand, some coffee beans require some time to fully reveal their potential. Like the coffee used by the 2019 Indonesian Barista Champion, which was roasted two months before his performance!
Find what works best for you and your coffee. Learn from your experience and draw your own conclusions. That's what makes coffee so intriguing.