By Jonathan Parent

Myths and legends:the freshness of coffee

When is coffee cooler How long can I keep my coffee without altering the flavors These are questions that come up often when buying coffee and to which we will provide some answers.s.

The following information is taken from aarticle written by Laura Perry, owner ofLuna Coffee in Vancouver and released in September 2020. It is based on a study published in theJournal of Agricultural and Food Chemistry dealing with the degassing of coffee. A modeling of the degassing rates allowed a structural and mechanical interpretation of the coffee bean degassing process. We have translated and popularized it for you.

How gas is formed in coffee?

During the roasting of coffee, thermal chemical reactions lead to the formation of gases, including a large production of carbon dioxide (CO2). A portion of these gases is released during roasting, while a portion is retained within the porous structure of the roasted beans and released steadily during storage or more abruptly during grinding and extraction. Along with degassing, CO2 can be formed during coffee extraction when the acids in the beans are neutralized by the hydrogen carbonate in the water.

The release of CO2 during the various stages of roasting for consumption is linked to many important properties and characteristics of coffee:
  • It is an indicator of freshness.
  • It plays an important role in shelf life and in packaging.
  • It influences the extraction process.
  • It is involved in the formation of crema. (see our article on crema)
  • It can affect the sensory profile at the cup.

Indeed, and in view of the multiple roles it plays, CO2 is an underestimated and little examined molecule in coffee.1 The degree of CO2 degassing depends entirely on the degree of roasting of the coffee. Light roast = more tightly trapped gas. Dark roasting = gas more easily released. The release of this gas occurs with the air, over time, but also when the water hits it: as when the hot water from your kettle reaches the ground coffee of yourFlowerDripper WhereAeropress.

The first time you brewed a lighter coffee, were you surprised how little bubbling (blooming) of your grind on contact with water, compared to the amount of the first active bubbling of a darker coffee When you brewed a cup of this full-bodied coffee a few days later, there was less effervescence, right??

Light roast does not react like dark roast

 Very light coffee will still have good bloom activity, even months after roasting. This flowering activity is relatively similar on the third day of roasting and on the 18th day. This is because the gas retained in the coffee bean evaporates at a much slower rate. This means that you may not taste the full potential of this coffee for at least a month after roasting. YES, ONE MONTH! It also means there's no need to panic if you've got a three-month-old light roast bag with some exceptional beans - they certainly haven't passed their prime. It may be the best ever tasted!s!2

Once all the gas is gone, the flavors gradually fade. In 6 months or more, the crisp, clear flavors you initially fell in love with will slowly fade away. Why As Jérôme Grenier-Desbiens, co-owner and head roaster at Roasters structure,

CO2 is not the only factor that contributes to the freshness of coffee. A panoply of aromas and light and delicate oils will gradually fade. In addition, once a coffee is exposed to oxygen, the essences of the beans degrade more quickly, resulting in a loss of freshness and notes. However, when the coffee is in a valve bag, the CO2 released helps dilute the oxygen level. Thus, we save these delicate little aromas that delight us. It is therefore advantageous to keep your coffee sealed, in its original valve bag. Once opened I recommend drinking the whole bag within 8-10 days.

Light roasting:
Contains less CO2
Less porous grains: degassing little and slowly
Ideal consumption, unopened bag: after 2 weeks to 3 months +

Medium roast:
Contains a little more CO2
Grains a little porous: degassing a little more quickly
Ideal consumption, unopened bag: after 14 days to 2 1/2 months

Dark roasting:
Contains a lot of CO2
Porous grains: degassing quickly
Ideal consumption with the unopened bag: after 7 days to 2 months

To limit exposure to oxygen after opening your coffee bag, you can maintain the freshness a little longer by using avacuum container.


Here is a table showing an experiment of degassing Arabica coffee (average value of 24 h)



Further studies need to be carried out to better understand the possible distinction between free CO2, which can be released during the degassing of dry whole or ground coffee under ambient conditions, and bound CO2, which is only released during wetting of the coffee or else. released at a slower rate and over very long periods of

Why is it better to keep your coffee beans?

The degassing time for ground coffee is shorter than for whole beans. Up to 75% of the gas trapped in coffee is released during and immediately after grinding (within 90 seconds), for a freshly roasted coffee. A big difference in degassing would be related to the destruction of the structure of the internal pores of the beans during grinding and the increase in the surface area of the ground coffee compared to whole beans, which causes the CO2, which was trapped, to be released quickly.

More caffeine = more outgassing Yes! The difference in degassing between Arabica (up to 3.0 mg / g) and Robusta (2x + caffeine, degassing up to 3.9 mg / g) is probably due to a higher sucrose content and in carbohydrates in Robusta coffee, therefore to a higher production of CO2.

The degassing time does not appear to be the same for dark roast and ground coffee. The total amount of gas released initially increases with the degree of roast, but plateau at darker degrees of roast. The results show that if there is a greater proportion of CO2 in the dark roasted beans (trapped in the larger pores) there will be a higher loss during grinding, but less rapid degassing once the coffee is ground. The explanation would be that the darker the coffee is roasted, the more it has a great affinity for the adhesion of CO2 after grinding. Part of the CO2 therefore remains fixed a little more firmly on the coffee particles.

Although the rate of CO2 rejection increases with the degree of roasting, the rate of CO2 outgassing in ground coffee, on the other hand, is highly dependent on the size of the grind and the roasting temperature. Coffee roasted by a high-temperature, short-term process has a significantly higher rate of CO2 degassing than those roasted by a low-temperature, long-lasting process.


2. Enjoylunacoffee