Why do we ‘rest’ coffee beans before brewing?
We love freshly roasted coffee because of all of the wonderfully fresh aromatics and lively flavours that make it so delicious! For that reason we’ll never let coffee leave the Dear Green roastery if it is more than one week from the roast date. However for consistency of flavours in your cup we recommend waiting a few days before brewing to ensure a perfect coffee! Here’s why...
The science! When coffee is roasted, a series of chemical reactions in the bean result in complex flavours and aromas. Much of the aroma is carried in the Carbon Dioxide (CO₂) which is expelled from the bean during and after roasting. This CO₂ is a byproduct of the roasting process and is the reason why many a coffee bag is fitted with a one way valve, allowing the CO₂ to escape the bag without allowing any air to enter which could stale the fresh coffee.
CO₂ is further released when beans are ground and then again when in contact with water. If you use freshly roasted coffee immediately after it is roasted, the gas, when released, can push against the brewing water creating a barrier and making it more difficult for water to be absorbed by the coffee grinds.
The unpredictable release of gasses in super fresh coffee can result in channeling and inconsistency in each cup and and uneven extraction of flavour compounds from the ground coffee. If coffee isn’t allowed some time to rest, each cup of coffee prepared could essentially taste very different from the next even when all brewing recipe parameters (dose, time, yield) are controlled accurately! Annoying eh?
Espresso is a sensitive beast. The variance in brewing with extremely fresh coffee can be most noticeable in espresso brewing which is a finer grind, brewed under pressure in a short amount of time making it more sensitive to fluctuations in flavour.
Fear not! The commonly accepted solution is the process of ‘resting’ coffee, allowing the beans to de-gas to a point where the coffee will extract all of the desired flavours and aromatics consistently, pretty much in all of the coffee shots!
But don’t take our word for it! There are of course various schools of thought when it comes to resting coffee. Most specialty coffee professionals will leave their coffee (for espresso) to rest for 14+ days. However there are some roasters experimenting with 1-6 month resting time and having great results. What is unanimous is that fresh coffee, merely a day or few from roast date will be far too volatile to work with...
Filter coffee however is a whole different story and way more forgiving! The grinds are bigger, the brew time is longer and there are less noticeable issues as the CO₂ isn’t fighting against pressurised water. It’s important to still have some control here though! Most specialty coffee professionals will rest filter coffee for up to 14 days and as always will still have to tweak recipes regularly to maintain perfect results! Just like espresso, regular dialling in is the key to continued filter coffee happiness!
If your coffee is too fresh CO₂ can absorb into the water, which will create carbonic acid; ultimately leaving the coffee with a ‘flat, sparkling water’ flavour sensation or a generally unbalanced acidity and lack of sweetness.
If your coffee isn’t fresh enough it is at risk of oxidation. A coffee that has oxidised will have lost its positive aromas and CO₂. When you extract this coffee it will have little to no crema and the flavours will be flat, dull with a distinct lack of acidity and a woody aroma.
The moral of the story… give it a rest! We Guarantee you’ll notice positive results!