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The Truth About Fresh Coffee
18-10-23
Written by Zoe+Ted
We’ve all heard people say that freshly ground coffee is better than buying it pre-ground. What about freshly roasted coffee? Is it best to drink coffee just a day or a week from the roast date? Does the idea of grinding fresh create a misconception that coffee must be used as close to the roast date? As it is ‘freshly roasted’? Well, we’re going to explore this idea of freshness, the science and research it has to offer us and how we can drink our coffee at its flavour peak.
DEFINING FRESHNESS
In a study by Samo Smrke, a coffee scientist, and other researchers - freshness is as close as possible to unimpaired retention of the qualities of freshly roasted coffee. In simple terms, it would mean that coffee's freshness is determined by it retaining all of its qualities and aroma. An issue with freshly roasted coffee is the high levels of CO2 present, created during the roasting process. According to the study, approximately 1% of the weight of freshly roasted coffee is CO2, a gas formed during the roasting process.
How did the CO2 get there?
Diving into a bit of high school chemistry, the CO2 is formed by chemical reactions during the roasting process such as the Maillard reaction and Strecker Degradation (I will link these studies below if you’re keen to continue down this rabbit hole). Depending on how dark the coffee is roasted will also affect the amount of CO2 trapped in the beans. Lighter to medium roasted coffee will store less CO2 because the beans' cell structure is mostly intact, meaning the beans are less porous. Darker roasted coffee has gone through the first and maybe even second crack too, resulting in a more damaged cell structure that is more porous, enabling it to store more CO2. There are a few other factors that can contribute to the amount of CO2 stored in the beans such as variety, country of origin, process and roast speeds, but that’s enough science for one day.
The thickness of crema on an espresso is also an indication of how freshly roasted the coffee is. The formation of the crema is a combination of CO2 bubbles and oils being extracted. Preference plays a part in this as some people see a thick crema as an essential part of pulling a shot of espresso. To others, it is a less desirable characteristic, allowing the espresso beans to degas before use. While grinding the beans speeds up the release of CO2 from the coffee, the bloom/preinfusion step in brewing, allows some of the CO2 to be released as well. The common factor in all of this is that the volume of CO2 impacts the extraction of coffee whether that be through consistency or flavour.
So, if freshly roasted coffee stores a lot of CO2, is that its true flavour peak?
You may be wondering about your coffee losing flavour or aroma. Well, most coffee is packaged with a one-way valve that allows CO2 to escape and keeps oxidation from happening. Oxidation is what kickstarts the degradation of aroma. The study showed that the rate of aroma loss is significantly slower compared to the loss of CO2. The amount of CO2 released from the coffee from the day it was roasted starts to flatline after about 20 days depending on the roast. So, CO2 in the coffee beans will decrease exponentially within that period. This is the resting period, allowing the coffee beans to degas and when it's time to brew you will have more consistent and better tasting brews.
What happens when your full bag of coffee has degassed?
POV: You've let your 250g bag of coffee rest for 21 days and it might take you a matter of days or another month to drink but you don't want your coffee to lose flavour. What’s next? Well, a few of our practices here at the roastery might help you decide what's best for you. The first would be to either keep it in the bag it came in which should have a way of resealing and keeping oxygen out. If not, you can keep it in an opaque vacuum/airtight canister free from air and light. Secondly, you could freeze your coffee, this will completely slow down the ageing process and degradation of aroma. You could even go the extra mile and pre-dose the bag to avoid condensation.
However, it’s really up to you, the beauty of coffee is that it has no actual rules. You can try and experiment on an array of things and you might find something you love that others might not enjoy. Hopefully, this just helped shed a bit of light on what’s happening to your freshly roasted coffee.
Links to sources/further reading:
https://www.baristahustle.com/blog/strecker-degradation-in-coffee-roasting/
