Green coffee beans are sensitive to a number of external factors, such as moisture and heat. They should be stored in a clean, dry, and well-ventilated warehouse in sealed bags, and placed on pallets to be raised above the floor.
If stored in areas with high temperatures and humidity, the coffee loses its flavours quickly and even take on an undesirable taste.
But what about freezing green coffee?
While the practice of freezing roasted coffee beans is becoming increasingly popular, storing green coffee in below-zero temperatures is still a reasonably new concept. To explore the practice more, I spoke with two coffee professionals based in Kenya.
You may also like our article on whether you should be freezing your coffee.
Staling and moisture content
Green coffee is hygroscopic. This means it absorbs moisture easily, even from the atmosphere.
Consequently, keeping it dry and cool is important. Any strong odours (especially those contained in liquids) will pervade the green coffee and artificially flavour it. This is why there is a need to store green beans in clean and contaminant-free areas.
As well as being dry and cool, green coffee warehouses and other storage facilities should also have good airflow and be free from dust. Optimal storage conditions are essential, as green coffee is not a long-term stable product, and will lose its flavour within at least 2 years.
But, what about storing coffee at subzero temperatures?
Despite the more traditional storing methods, freezing green coffee is one of the newer ways people have been using to preserve freshness.
Dr. Christopher Hendon is an assistant professor at the Department of Chemistry and Biochemistry at University of Oregon. He has conducted extensive research into the impact of temperature on coffee quality and extraction.
“For every 10ºC you cool something down, most of the processes occurring in the bean occur at half the rate,” he explains in this article. “So, [the] cooling of coffee should prevent chemical reactions that occur over time (like staling or aging), by making them proceed extremely slowly.”
But what about cup quality? What kind of impact does freezing green coffee have on the end product?
In research conducted at the Dedan Kimathi University in Kenya on freezing green coffee, it was actually found that the cup quality of frozen coffee scored higher marks than coffee stored at room temperature.
Nancy Warui is a licensed Q grader, and was present on the tasting panel for these frozen green samples.
“It’s all about science,” she explains, “At such low temperatures, the activities within the bean slow down a lot which retains the freshness of the beans.”
After milling, the green coffee she cupped was stored in perforated bags (similar in structure to jute bags) and then placed in the freezer immediately. The freezer was free of any odours and other contaminants that could have compromised the quality of the beans.
The beans were under observation for 75 days where any changes were monitored regularly, including water activity and moisture content.
Juliet Murugi was also on the panel conducting the sensory and cupping evaluation of the coffee. She noted the significant change to water activity in the frozen green beans.
“The major observation was how the coffee in the freezer lost some moisture in the first 3 weeks, after which no more moisture was lost,” she tells me. “After 3 weeks, the moisture content totally flattened and continued that way until the end [of the study].”
Effects on cup quality
During the research carried out by Dedan Kimathi University, a panel of five cuppers evaluated the frozen green coffee samples. All of them agreed that the coffee had unique aroma, flavour, and body characteristics.
“Immediately after removing the samples from the freezer, we roasted it to about a medium level, ideal for cupping,” Nancy says. “After grinding we noticed the rich aromatic fragrance of the frozen coffee.”
Juliet adds: “It exceeded my expectations. You immediately notice the heavier mouthfeel – the full body of the cup is exceptional.
“The acidity was bright and the flavour was sweet, with an unforgettable aftertaste.”
Nancy adds: “I liked the fullness of the cup In comparison with the normal lot. It had a more agreeable flavour, sharper acidity, and [was] more balanced.”
The paper they contributed to found that with frozen green coffee, the key to retaining freshness – and therefore flavour intensity – is maintaining moisture content.
Reduced humidity in the freezers meant that the beans did not absorb any water from the atmosphere. Although moisture levels fell by 2% within three weeks of freezing, it remained stable for the rest of the research period – only dropping by a further 0.5%.
The findings concluded that the moisture contained within the bean condensed, and therefore could not escape from the beans. All microbial activity that occurs inside the beans slowed by more than half the usual rate due to the temperature.
This means that the freshness of the beans was preserved and when the bean was finally roasted, the quality was high.
It is also important to note that several different grades of coffee were used in the experiment, indicating that all of the green coffee samples behaved similarly.
Challenges when freezing green coffee
Despite this advantage of preserving freshness, freezing green coffee is not often as straightforward as it seems. The main challenge is safely freezing green beans without compromising quality.
Moisture and humidity are green coffee’s worst enemies, and these are two things which are definitely present in freezers, especially those that are not well-maintained and contain frost.
Storing green beans in a frosted-over freezer may lead to significant quality deterioration when the coffee thaws – especially with more complex-tasting coffees.
Water activity in thawed beans may also be less predictable than green coffee stored at room temperature. This could negatively affect the process of roasting, and lead to anomalies in roast profiles. This is something that roasters buying any kind of frozen green coffee must consider.
If other products are also stored in freezers along with green coffee, they may also negatively influence coffee quality. This is because the beans are likely to absorb any odours. Roasters should take extra precaution where they store frozen coffee and ideally keep other products in separate freezers or compartments.
However, this ultimately leads to increased costs, which can become a risk if sales of these frozen coffees are not proportional to the roaster’s investment. Piloting a small-scale trial of marketing and selling frozen green coffee may help roasters figure out if it is a viable option.
Best practices for coffee roasters
These experiments suggest that frozen green coffee may maintain cup quality better than green coffee stored at room temperature.
“If roasters had bags of previously frozen green with unique cup characteristics, they would fly off the shelves,” Juliet says. “Consumers would immediately notice the extra sweet [and] smooth taste.
“This makes a lot of sense, but, of course, they would have to pilot the project first. However, I have no doubt there would be a lot of interest in this coffee.”
Charging premium prices for frozen green beans would also be necessary, because of the added costs of purchasing the extra equipment to freeze and monitor the coffee.
However, consumers may be likely to pay a premium for the rarity and exclusivity of this coffee itself – particularly in markets where customers value exclusive lots and unusual processing techniques.
Before roasting, green coffee should be stored in airtight and waterproof bags, and thawed immediately before roasting to ensure best results.
Finally, take some precautions. Avoid storing green coffee alongside other food products and ensure the freezer is clean and free from frost. Finally, make sure humidity and temperature levels are regulated. Improper storage may lead to defective beans.
For roasters looking to differentiate themselves and consumers who want the freshest coffee they can possibly try, there may be an opportunity with frozen green beans.
When frozen properly, green coffee can stay fresh and vibrant for extended period. This ensures cup quality is maintained, and is hugely beneficial to roasters looking to offer premium, unusual, or exclusive coffees.
While more research is needed to fully understand the chemical reactions that take place inside green coffee when frozen, freezing it may be a worthwhile venture for those who want to maximise freshness.
Enjoyed this? Then read our article on how packaging material impacts green coffee quality over time.
Photo credits: Peter Gakuo, Battlecreek Coffee Roasters on Unsplash
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