There's always this notion of freshly roasted beans being the best and most sought after. But have you ever brewed a coffee that is over 1 month old and it still tasted good? Not "not bad", but actually good? Here's a provocative thought: if you see a coffee roaster touting freshness as one of their selling points, they are probably average at best.
Why? Because to an artisanal roaster, fresh coffee is the norm. The thought of old or stale coffee is so far removed from their reality that they don't even think of freshness as something worth shouting about.
And is freshness really so important? As with all things coffee, it depends.
The determining factors: Roast color and speed
The biggest determining factor in how fast your coffee stales/degasses/ages is the degree of roast and the roast speed.
*Excerpt from: Time-Resolved Gravimetric Method To Assess Degassing of Roasted Coffee
As you can see from the above research by Samo Smrke and his team, the roast degree impacted the rate of degassing in the coffee beans significantly. Darker roasts degassed as a much faster rate compared to lighter roasts. Similarly, faster roasts degas at a much slower rate.
This suggests that you would need to rest your coffee for different periods of time based on how light/dark your coffee was roasted and to a lesser degree, how fast it was roasted to that color. This goes back to the porosity of the coffee caused by the roast factors which we cover in How coffee roasting affects your brew recipe.
But what is the point of degassing?
Why rest your coffee?
A freshly roasted coffee contains a load of Carbon Dioxide (C02). This C02 then gets released partially when you grind the coffee, but more importantly, when it comes into contact with water. Therein lies the problem.
Lots of CO2 bubbles in your coffee means that water is not getting through to your coffee. Instead, it is getting blocked by these pockets of air. This is why we have the blooming/stirring/swirling stage at the beginning of almost every pourover brew recipe. However, it's not a perfect solution and we don't have an option of stirring or swirling in espresso.
So should we grind the coffee and intentionally let all the CO2 out?
Not exactly. Along with CO2 are other volatile gases that gives coffee its heavenly aromas that we all love. So, if we were to intentionally purge all the CO2 out, that would also mean taking out all the lovely aromas in the coffee.
The key is to strike a balance between degassing CO2, but also retaining the volatile aromas. This is what we refer to as the ideal rest time. It is fairly obvious that the dark roasts degas and "stale" much quicker than medium and light roasts. This is especially so for faster roasts. As a result, there is a ton of advice out there recommending super fresh roasts and coffees to be consumed quickly. Because believe it or not, majority of coffee production still belong in the medium to dark roast category.
But this doesn't apply to most third-wave coffee roasters which tend to be in the medium to light roast category. In fact, many of these coffees perform better when brewed after longer rest periods of 14 days and beyond. Now of course, if your coffee is unevenly roasted then that's a different story.
Here's a basic guideline for resting your roasted coffee:
Dark Roast (Ground Agtron 60 and below): As fresh as possible. At 1-3 days old it is already far beyond the degassing levels of medium and light roasts. Starts to oxidize and really taste acrid after a week or so.
Medium Roasts (Ground Agtron 60-80): Minimally 5-7 days for filter brewing and 7-10 days for espresso. Usually lasts at least a good month or two before noticeable deterioration of flavours.
Light Roasts (Ground Agtron 80+): 10 - 14 days for filter and 14 days+ for espressos. These are really long lasting, some Nordic roasters with ultra-light roasts even have up to 6 months as their best before date.
If you come across coffees significantly out of these guidelines, you'll understand that the coffee is probably not ideal. Yes, especially those coffees in supermarkets with 2 to 3 year shelf lives.
Of course, there are other factors like heat, exposure to oxygen, water and light that can accelerate the "staling" process so make sure to follow the common guidelines for storing coffee.
To learn more about coffee roasting, check out our Ultimate Coffee Roasting Course. Or if you want to enjoy some awesome coffees, check out our amazing co-roasters and more at Beans.sg!