Mechanism of CO2 formation and release
The roasting process activates a series of complex thermochemical reactions, such as the Maillard reaction, caramelization, and Strecker degradation. These reactions not only create characteristic flavors but also generate a large amount of carbon dioxide (CO2) trapped within the porous structure of the coffee beans after roasting.
Gas release or degassing is the natural phenomenon of releasing this accumulated CO2 into the external environment. This gas release process occurs continuously from a few days to several weeks after roasting. The rate and extent of gas release directly affect the quality of extraction and the freshness of Specialty Coffee beans.
Transformation of volatile compounds during the degassing phase
Alongside the CO2 release process, the volatile organic compounds that construct coffee aroma also change continuously over storage time:
- Aldehydes and Alcohols: Typically impart fruity, fresh, and natural floral notes in the early stages after roasting. However, this group of compounds is highly susceptible to reduction or transformation due to oxidation.
- Pyrazines: Contribute secondary notes such as roasted nuts, cereals, and chocolate, with slightly higher mechanical stability within the bean structure.
- Furans: Provide caramel sweetness but evaporate quickly if packaging conditions are not airtight.
Strictly controlling storage time helps preserve the golden ratio between these compound groups, preventing the disappearance of fruity and floral notes and their replacement by negative flavors.
Impact of degassing time on Cupping sensory scores
In cupping technique, degassing time determines the accuracy of sensory evaluation through two extreme states:
When degassing time is too short (Coffee is too fresh)
Excessive residual CO2 within the bean structure releases vigorously upon contact with hot water, creating a physical barrier that prevents water from directly contacting the coffee grounds. This phenomenon hinders the extraction process, resulting in weak coffee lacking body and exhibiting sharp acidity, astringency, and a slight tingling sensation on the tongue due to dissolved carbonic acid.
When degassing time is too long or storage is poor
The continuous decline of volatile compounds combined with the oxidation of natural fats in the beans leads to rancidity. Coffee loses its original fruity and floral notes, clean cup scores drop significantly, and negative flavors such as earthy, smoky, or woody notes emerge.
Influence of temperature and storage conditions during the degassing phase
Ambient temperature acts as a direct catalyst for the kinetics of the degassing process and chemical transformations:
- High temperature: Accelerates the rate of CO2 release but simultaneously causes rapid loss of volatile aromatic compounds, accelerates fat oxidation reactions, and causes the beans to stale quickly.
- Cool and stable temperature: Helps slow down the gas release rate in a balanced manner, maintaining sweet notes, chocolate aromas, and protecting the delicate aromatic structure of specialty coffee.
- Specialty Coffee Association Research — https://www.scaa.org
- Coffee Chemistry and Degassing Insights — https://www.coffeechemistry.com
- Specialty Coffee Extraction and Degassing — https://www.specialitaly.com