Does grinding frozen coffee damage your grinder?
In recent years, we have seen an increasing number of specialty coffee shops and roasters freezing roasted coffee beans. There are several reasons for doing so, but the main argument is simple: to preserve freshness for as long as possible.
Traditionally, storing roasted coffee in a cool and dry place has been the most common way of maintaining freshness. However, in light of the numerous benefits of freezing coffee, it seems as though more and more coffee professionals and enthusiasts are taking this approach, too.
This then leads us to an important question – does frozen coffee damage your grinder?
To find out, I spoke with the Managing Director at Colonna Coffee, Maxwell Colonna-Dashwood, and Assistant Professor of Computational Materials Chemistry at the University of Oregon, Dr. Christopher Hendon. Read on to find out what they had to say.
You may also like our article on single-dose coffee grinding.
Why is coffee frozen?
For a long time, both coffee professionals and consumers alike believed that storing roasted coffee in cool and dry conditions was the best way to maintain freshness.
This is because the roasting process irreversibly changes the cell structure of coffee beans. Once roasted, coffee is more susceptible to a number of environmental factors, such as heat, light, moisture, and oxygen.
Ultimately, when freely exposed to these factors, coffee loses its distinctive flavours and aromas more quickly, eventually becoming flat-tasting and stale.
However, it’s been impossible to ignore the growing number of coffee shops, roasters, and even consumers who have started to freeze their roasted coffee. Some of the most notable roasters to do so are ONA Coffee in Australia and Proud Mary in Australia and the US, who typically freeze their exclusive and limited-edition lots.
Moreover, in his 2017 US National Coffee Championship routine, winner Kyle Ramage used dry ice to freeze his coffee beans before grinding. Kyle’s decision to grind his coffee from frozen largely stemmed from a 2016 study entitled The effect of bean origin and temperature on grinding roasted coffee.
Maxwell, who co-authored the research paper, explains that there are two main benefits to freezing coffee.
“Frozen coffee beans grind better and you can store them for a longer period of time,” he tells me. “You can freeze coffee for just a few hours before grinding to experience the benefits of better grinding.”
The study found that grinding frozen coffee led to more uniform particle size distribution, which can help to extract a wider range of flavours and aromas.
“However, you still need to store the coffee in an airtight container with low oxygen headspace in the freezer, otherwise it may lose some of its original quality,” Maxwell says.
Christopher also worked on the study. He explains why minimising the presence of oxygen is so important.
“Freezing coffee in an air and moisture-free environment helps to prolong its freshness – which goes for both roasted and green beans,” he says. “In our lab, we use food-safe vacuum sealers, and we have found that the quality of the bags makes a significant difference in terms of preserving freshness.”
In line with this, many coffee shops and roasters freeze coffee as single doses, sometimes in glass or plastic tubes to ensure there is as little oxygen present as possible. This means a single dose of coffee can be removed from the freezer and then ground using a single-dose grinder.
What about freezing green coffee?
Much like it does with roasted coffee, freezing green coffee helps to prolong freshness and flavour.
As coffee is a seasonal product, roasters need to manage their inventories according to harvest times – which means freshness is an important consideration. Generally speaking, green coffee is considered fresh between six and 12 months after harvest.
“Green coffee freshness depends on a number of factors, such as origin, processing method, and level of water activity,” Maxwell explains. “Different coffees will age and stale at different times.
“Freezing green beans means coffee shops and consumers can buy expensive or exclusive coffees and they don’t have to worry about roasting them within a few months,” he adds. “Some coffee shops and roasters have ‘frozen’ menus which can read like an expensive wine list.
“It’s exciting,” Maxwell continues. “It’s an opportunity to extend the freshness of some really interesting coffees.”
Is it better to grind frozen coffee beans?
Alongside prolonging freshness, grinding coffee from frozen can actually ensure that the beans grind more evenly.
“Our research showed that the particle distribution changes because frozen coffee is more brittle [than coffee at room temperature],” Maxwell explains. “Also, as you grind finer, the grinder produces a lot more heat which can destroy the flavours of the coffee.
“Grinding coffee from frozen can help to protect its flavours,” he adds.
Maxwell explains that while conducting the research, this was particularly prevalent with more aromatic coffees which had fruity flavours.
“When conducting blind tastings, it was found that the frozen coffee scored higher, with higher recorded levels of aromatics and acidity,” he says. “This is because these aromatics are volatile compounds, so they are more likely to be destroyed and lost while the coffee is being ground.”
However, Christopher tells me that further research is needed to understand whether this is true for different types of coffee, including different origins, processing methods, and flavour profiles.
“We don’t know this yet,” he says. “These kinds of longitudinal studies would be interesting and valuable to the coffee industry.”
Do frozen coffee beans damage your grinder?
Before discussing how frozen coffee affects grinders, we need to understand whether it causes any damage to the beans themselves.
“Some of these concerns aren’t particularly well researched, but limited results show that freezing coffee has little effect on the beans in any way – for both green and roasted coffee,” Maxwell says.
“If you think about a tomato, which is 90% water, if you freeze it then the water crystallises and destroys the cell walls – and then you have a mushy tomato,” he adds.
Roasted coffee, meanwhile, has approximately 2% moisture content. Ultimately, this means freezing roasted coffee beans has little to no impact on cell structure – which has already been irreversibly changed by being roasted.
When it comes to potential damage caused to grinders, Maxwell says the answers aren’t fully clear.
“There is concern about grinding frozen coffee as it can attract condensation, which can cause water damage,” he explains. “This could damage the burrs over time, but the evidence is inconclusive.
“Some grinder manufacturers don’t recommend grinding coffee from frozen,” he adds.
Christopher, meanwhile, says that grinding frozen coffee shouldn’t cause any damage to grinders.
“Manufacturers suggest not to grind coffee from frozen coffee because the coffee is ‘mechanically’ dissimilar to room temperature roasted coffee,” he tells me. “In our 2016 study, we found that it’s likely that coffee undergoes some kind of transition around 0°C, which suggests that something ‘mechanically’ changes in the beans’ cell structure.
“However, we don’t think this change affects the grinder at all,” he adds. “Roasted coffee will only be at its ‘hardest’ if it is roasted to pure carbon [or burned], and even then it is significantly less hard than titanium or steel, which are commonly used materials for burrs.”
Other concerns that some may have about freezing coffee are the increase in waste as a result of single dosing.
“When freezing coffee, coffee shops and roasters use individual doses, which can be wasteful,” Maxwell says. “They’re not freezing a kilogram of coffee and then putting it in the grinder hopper.”
Christopher agrees, saying: “The challenge with grinding large quantities of coffee is that it takes time, so by the time the coffee is ground, it may have heated up.
“Ultimately, you need to grind it quickly,” he continues.
However, Christopher adds that when talking about waste from freezing coffee, it’s important to understand the wider context of sustainability in the coffee industry.
“I encourage people not to focus too much on this because it’s a minor issue compared to other environmental impacts in the supply chain,” he tells me. “Of course, we want to minimise waste, but freezing coffee is helping to preserve and prolong the shelf life of coffee which probably has a significant carbon dioxide footprint.
“To let that coffee go stale and lose its freshness would also be a tremendous waste,” he concludes.
Although it’s a topic of clear discussion, grinding coffee from frozen has clear benefits. However, there isn’t much clear evidence about the effect of frozen coffee on grinder burrs. Nonetheless, baristas and consumers alike should be careful – especially when it comes to condensation buildup on grinder burrs.
It’s likely that the trend of freezing roasted and green coffee will continue, so further research on how frozen coffee impacts grinder performance is paramount.
Enjoyed this? Then read our article on what the future is for espresso.
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