How Can Roasters Control The Ageing Of Green & Roasted Coffee?

Peter Lancashire
March 25, 2021
green beans

Not to be confused with “old” or “stale”, ageing is a fundamental process involved in the production of quality coffee. In simple terms, it is allowing both green and roasted coffee beans time to “rest” to enable the full development of flavours and aromas.

While in recent years, there has been a rise in the demand for fresher coffee, beans still require a period of ageing to reach their maximum potential. Green beans roasted too soon after processing can lack depth and taste grassy, while roasted coffee brewed immediately after roasting can result in an uneven extraction.

To find out more about the ageing of coffee, I spoke with expert roaster and 2018 German Barista Champion, Nicole Battefeld.

See also: Does Compostable Coffee Packaging Prevent Exposure To Light?

green coffee ageing

Why Does Coffee Age?

The ageing of coffee is an important stage in the long journey from seed to cup. Not to be mistaken with staling, it is a process in which green and roasted coffee is allowed to rest for a certain period of time to allow its characteristics to develop.

The concept of ageing coffee has existed for centuries. Imports of coffee from Yemen to Europe in the 17th century would have to undergo long voyages by sea, often up to several months. During this time, the unroasted beans would change considerably due to the conditions on the ships.

As journey time reduced to a matter of weeks, the ageing of coffee increasingly took place at origin, where the effects of a sea voyage were imitated. In recent years, many people have shown a preference for fresher coffee with shorter ageing times; however it’s generally agreed that green coffee still needs time to rest before being roasted. This time can vary anywhere from six months to three years depending on customers’ tastes.

Nicole Battefeld works as a barista, roaster, trainer, and competitor. Based in Berlin, she was crowned German Barista Champion in 2018 and finished fifth at the 2019 World Coffee in Good Spirits Championship. She tells me ageing is fundamental in developing the flavour of coffee.

“Ageing can definitely be both a good and bad thing for the flavour of green beans,” she says. “Unroasted coffee can’t be used immediately after it’s been processed and dried; it needs some time to lose it’s grassy taste. Remember, its cellular structure has undergone significant pressures during processing. In my opinion, it needs at least a couple of months to settle before the roaster can bring out the best flavour from it.”

On the other hand, if green beans are aged for too long, they can start to lose their distinct characteristics, particularly their acidity. Aroma and flavours tend to develop until reaching a “sweet spot”, after which they will start to degrade. The point at which this occurs depends on a number of factors, including origin, density, variety, and storage conditions.

green coffee age

The Importance Of Green Coffee Storage

When green coffee is ready to be shipped to buyers, they will usually have reached a certain moisture content percentage (~11%), which enables them to be packed away into sacks and shipped without risk of mould forming.

Once the beans reach their destination, they need to be stored appropriately. Nicole explains that, ideally, they should be kept at a low, stable temperature to help them reach their optimum.

“A well-climatised storage unit can help improve the ageing of green beans,” she says. “Constant temperatures and low humidity without direct sunlight is best. 

“Preferably, the coffee should be stored in vacuum-sealed bags, as it will last much longer than when it’s in normal hessian sacks. Hessian sacks are great for keeping the beans aerated during shipping, but once they arrive, you want to limit exposure to oxygen, as this will only speed up the ageing process.”

Indeed, vacuum-sealed bags are widely considered the best for storing green coffee beans. Not only do they prevent oxidation, they also keep out moisture and odours, which can negatively affect the flavour of the coffee. Alternatively, roasters may consider using hermetically sealed GrainPro sacks, which is cheaper than vacuum sealing, but slightly less reliable. 

Nicole warns that roasters must make accommodations for the arrival of large quantities of green coffee. If they don’t have the capital to invest in green storage facilities of their own, she recommends storing the beans in a specially designed warehouse.

“Unroasted coffee beans take up a huge amount of space,” she explains. “As a result, I tend to store all my deliveries in a warehouse at a port. I can then order smaller amounts as soon as I need them, which is common among roasters.”

Generally, most larger green importers have their own warehouse spaces. This allows dedicated professionals to watch over the beans you’ve purchased without having to worry about quality being affected. 

“The downside is that I can’t personally control the environment or temperature of the room,” Nicole says. “If I could, this would be a massive benefit, as I could oversee the different variables that influence the quality of coffee.”

roasted coffee age

Does Coffee Continue To Age Once It’s Been Roasted?

When coffee is roasted, a number of volatile gases build up inside the beans, most of which is carbon dioxide (CO2) After roasting, the built-up CO2 immediately starts to escape in a process known as “degassing”.

Within the first 24 hours after roasting, the level of CO2 inside the beans will have fallen by around 40%. While this rate decreases, CO2 will continue to be released over the following days and weeks.

The amount of CO2 has a significant influence on not only the freshness of the coffee, but also how it behaves during extraction. If the beans have too much CO2 when ground and brewed, it can leave an unbalanced taste in the cup. Air pockets caused by the CO2 disrupt contact between the coffee grounds and the water, leading to an uneven extraction of the flavour and aroma compounds.

However, like green coffee beans, putting a specific time on how long roasted coffee needs to degas before it reaches its optimum depends on several factors.

“Variety, processing methods, roast profiles – these can all affect the rate of degassing. I couldn’t put a single date on how long coffee should be allowed to degas. But usually, filter roasts peak between five and 30 days after roasting, while espresso roasts peak between 10 days and two months.

“My recommendation is to taste-test each coffee and monitor how the flavour develops by brewing them and writing down how any changes you’ve noticed. This represents time well spent as the research will help improve knowledge of coffee for those who work in the industry.”

Like green coffee, the bags in which the coffee is stored are crucial, especially as the roasted coffee will likely spend time on a shelf or in a cupboard at home. Multilayer packaging is a good option as it helps prevent exposure to external factors such as light, oxygen, and moisture. Attaching degassing valves, which allow CO2 to escape without letting oxygen in, should also be considered.

recyclable packaging

Whether letting green beans rest after harvesting or allowing roasted beans to degas after roasting, ageing plays an important role in the development of coffee. However, to ensure that coffee doesn’t become mouldy or stale, specialty roasters must control the ageing process by taking a series of measures.

At MTPak Coffee, we offer a range of coffee packaging options that will keep your roasted coffee fresh, while allowing it to age sufficiently. After choosing from our selection of sustainable materials, including kraft paper, rice paper, PLA, and LDPE, you can opt for BPA-free degassing valves, resealable zippers, and aluminium ties to prevent oxidation but letting CO2 escape.

For more information on our sustainable coffee packaging, contact our team here.

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