A mistakenly widespread idea among coffee enthusiasts is that you should buy coffee beans with a roast no older than a month if you’re preparing espresso. But there are even those who claim that anything other than consuming coffee within the week after roasting is a waste.
However, my experience is different. In search of that “perfection” that all espresso fanatics pursue at some point in our lives, I tried to buy increasingly fresher coffee — if it could be only coffee roasted a few days ago, even better. But as paradoxical as this may seem, that almost manic search did not lead me to better coffee.
On more than a few occasions, those coffee beans roasted just a couple of days ago resulted in espressos that were flat, without intensity, complexity, or nuance in their flavor. However, I clearly remember an occasion when I bought coffee beans whose package showed a roast date of over a month prior. Fearing the worst, I started calibrating the grinder for that coffee and — to my surprise — I got an absolutely spectacular espresso, and I spent about three weeks making one of the best coffees I’ve ever had at home.
What’s happening? How can it be that freshly roasted coffee beans taste so bland to me, and yet this other coffee, roasted over a month ago, tastes so good? Doesn’t it go against everything said in the barista world?
Well, there’s an explanation for everything, and for this too.
CO2: A Key Factor in the Days Following Coffee Roasting
When roasting coffee beans, two key reactions occur: the Maillard reaction and pyrolysis — chemical processes involving both sugars and proteins — which are responsible for the browning of meat when cooking it, the crispy crust of bread when baking, or the roasting of our beloved coffee.
During this process, a large amount of CO2 and other gases are released, but the porous structure of the coffee bean causes much of these gases to be retained within the bean itself. As a result, in the days — even weeks — following the roast, the beans undergo degassing. This is why coffee beans are not vacuum-packed, but instead stored in containers with valves that allow those gases and CO2 to escape.
This accumulated CO2 hinders extraction, as it forms an added layer of resistance, preventing uniform extraction and generally causing channeling problems — where water finds an escape route through the puck and more coffee is extracted from one part than from another.
This degassing is also to blame for ground coffee losing its freshness so much more quickly compared to whole beans. When grinding the bean, most of this gas is released — but this simultaneously accelerates oxidation, causing the coffee to lose freshness rapidly. Similarly, degassing explains why, as days go by, the same coffee bean needs to be ground finer and finer: over time, the bean releases those gases and, once ground, offers less resistance, so it needs to be ground finer to compensate.
The type of roast also plays a crucial role: dark roasts release more CO2 during roasting, trap less of it inside the bean afterward, and when ground, break down more easily and develop more water-soluble compounds, such as melanoidins and oils. In contrast, medium roasts release fewer gases during pyrolysis and the Maillard reaction, but the bean retains more of this gas long after roasting.
Therefore, it’s about finding the right level of CO2 in the bean: enough not to hinder a good extraction, but not so little that it has already been released, triggering the oxidation process. That sweet spot generally falls somewhere between 5 and 14 days after roasting.
Let the Coffee Rest a Week After Roasting
For espresso, it’s not necessary to use freshly roasted coffee beans — quite the opposite: it’s advisable to let them rest for a week, even two. More and more baristas and roasters are recommending this, and from my own experience, I can say they are absolutely right: I have often managed to pull a better espresso when using beans with a roast date of between two and three weeks.
Another myth worth debunking is the idea of never consuming coffee with a roast date older than a month. As I mentioned before, I have come across coffees roasted over a month ago and still managed to extract espressos with fantastic flavor and aroma — although it is true that this is much more common with medium roast beans.
And as I mentioned earlier, medium roasts release gases more slowly and progressively than dark roasts, which means a medium roast bean stays fresher for longer, better preserving its flavor and characteristics. It’s a topic of ongoing debate, but there is growing consensus that a medium roast coffee bean can stay fresh for at least three months — and probably longer if it’s a light roast.
That said, it is incumbent on us as consumers to ensure that any coffee beans we buy — especially specialty coffee — have a recent roast date. With fresh beans, you are the one who decides how and when to consume that coffee; with supermarket coffee, you no longer have that choice and must settle for beans that have already lost their freshness. From a consumer’s point of view, freshly roasted beans are always the better option — and when it comes to specialty coffee, it’s not just better: it’s the bare minimum.
