One of the biggest myths in coffee is that all coffee is extracted better the fresher it is.
But that isn't always the case...
How does the freshness of a coffee effect extraction?
The freshness of your coffee has a direct impact on how readily it can be extracted when you brew it.
To understand why that is, we need to take a step back, and talk a bit about what happens to coffee beans during the roasting process.
When we apply heat to green coffee beans, we start a process of complex chemical reactions.
There's a lot going on chemically during the whole roasting process, but one of the main set of reactions is called the Maillard reaction.
The Maillard reaction is the process of caramelization, where the natural sugars inside the beans react with the amino acids. The sugars and the acids start to combine and they create something called melanoidins.
This process happens in lots of other food cooking situations too - think about searing a piece of meat, or toasting a marshmallow.
The visual result of this reaction is a browning of the beans.
But there's another biproduct of this reaction that you can't see: Carbon Dioxide.
Remember that chemistry lesson from high school....
Chemical A + Chemical B = Chemical C + Chemical D.
Well in this case it's:
Sugars + Amino Acids = Coffee Yummies + CO2.
As the acids and sugars combine, CO2 is released.
A lot of that CO2 is released into the roasting drum and escapes instantly.
But some of it remains trapped inside the coffee beans after the roasting process is finished.
Why does this all matter for coffee brewing?
That trapped CO2 inside the bean is a bit of a clingon.
It wants to cling to the coffee, and get in the way of the water.
And if the water can't get to all the yummies inside the coffee then it cant extract them either.
So we need to allow that trapped CO2 to escape, so that we can get fuller and more satisfying extractions, and tasty brews.
One way we do that with pourover brewing is with the bloom.
But, with lighter roasted coffees in particular, a bloom might not always be enough.
What is resting coffee?
Resting coffee is when we purposefully give a coffee time after roasting to "open up" before we start brewing with it.
As we learnt above, there are a lot of chemical reactions happening during the roasting process.
A biproduct of many of those reactions is CO2 or carbon dioxide.
CO2 gets trapped inside the coffee beans, and clings to the yummy stuff we want to extract.
Over time, that trapped CO2 will naturally leak out and escape.
But we need to give the roasted coffee some time, in order to let as much of those gasses escape as possible before we start brewing.
This process is called degassing.
The ideal amount of time each coffee needs to rest depends on a few things, but the biggest factor by far is roast level - how light or dark the coffee is roasted. We'll get more into ideal rest times a little later.
What happens if you don't rest coffee?
If you don't, or can't (for example, if you're out of coffee and only have a fresh 1-day-off-roast bag on hand), you're absolutely fine to brew and enjoy it. You'll still have a good time.
Just know that your cups will change and intensify in the days ahead as the degassing process continues and the coffee begins to open up.
How does roast level effect CO2 build up and rest times?
Light roasts produce less CO2 during roasting, darker roasts produce more.
But light roasts are more dense, so they hold onto CO2 for longer.
Conversely, darker roasts are more porous, and it's easier for the CO2 to escape.
So, are roast dates still important then?
Yes!
Knowing the roast date of your coffee is still very important.
Because knowing that helps you to figure out the optimal time to enjoy a coffee.
If you know the roast date and you know the roast level (i.e. is it a light roast? super light? dark roast?) then you can figure out a good ball park resting time.
Remember that roast level is the biggest thing that impacts optimal rest time.
| Roast Level | Suggested Rest Time |
| Very light | 2-4 weeks |
| Light | 1-3 weeks |
| Light-Medium | 5-10 days |
| Medium | 3-5 days |
| Dark | 1-3 days |
*Everyone's definitions of roast level are different, so use these suggestions as a rough guide only. We're just putting these here to give you a starting point.
What other factors can influence how long to rest a coffee?
There are some environmental factors that can either speed up or slow down the degassing process, and therefore impact your target resting times.
Temperature
In warmer weather and climates, degassing happens faster.
In colder temperatures, that process slows down a little.
If you live in a seasonal climate like we do here in Vancouver, where the winters are relatively cold and the summers hot, you might notice that your coffees degas a little bit differently at different times of the year.
Tips for degassing your coffee more quickly
One thing you can do, is to grind your dose a bit more ahead of time.
Weigh it out and grind it as you normally would.
Then put the grounds in an airtight container (a vacuum seal one like an Airscape or something similar, ideally), and wait for half an hour.
Patrik from April Coffee actually did this while competing in the World Brewers Cup one year, with a coffee that was roasted just 6 hours prior.
Grinding slightly in advance like this can help to speed up the degassing process and help the coffee open up more quickly than it would do in whole bean form.
Ready to put all your new found coffee resting knowledge to the test? Grab a bag of freshly roasted single origin coffee and try it out at different points "off-roast". See what differences you can taste, and where you like it most.
