Recently, the act of grinding coffee beans for the days’s cup struck me as pleasantly normal. Back when I was rushing off to an office and classroom, even something as small as grinding coffee was just one more obstacle to getting out the door. Whole bean coffee was in the “not worth it ” category, along with, at times, ironing. The semester from hell was over. Now, suddenly, I had a moment to appreciate the freshness and aroma of newly ground coffee. But what helps make coffee fresh? What keeps it fresh? And why does ground coffee smell so good?
Coffee beans undergo chemical reactions when roasted. This process creates hundreds of new chemicals.
Many of these chemicals are are good for you and and a few are bad. The good ones can “protect against gout (by lowering uric acid levels), tooth decay and gallstones… there is mounting and strong evidence for coffee providing some protection against type 2 diabetes.” Coffee might even prevent Alzheimers disease. Acrylamide is one of the few bad chemicals and more is found in in light roasts.
One thing that happens during roasting is the beans get lighter and more porous. The pores hold both carbon dioxide and the chemicals which give coffee its aroma. Of the many chemicals in coffee only a few are responsible for the aroma. Of these, a furan-2- methanethiol gets the most attention. Its odor has been described as a combination of nutty and burnt match. Clearly, the full range of aromas combine to give coffee its good smell. Medium roasts are most aromatic.
The good smell is created by less than 1% of the gases in coffee beans. Most of the gas trapped in the pores of a roasted bean is carbon dioxide. It makes up 1-2% of the weight of the roasted coffee.
Fresh coffee when brewed will have a delightful white foam called crema. This is made from carbon dioxide.
The way the coffee is roasted has a large effect on the gases trapped in the beans. Dark and medium coffees are highly impacted by roasting temperature and high temperatures release more gas–which you do not want. In the case of coffee, we want gas. Darker roasts are more porous and hold more gases to begin with. But the pores break down quickly when ground.
Keeping oxygen away is an important part of keeping coffee fresh. Carbon dioxide is found in highest concentrations in freshly roasted coffee. In a bag of coffee, carbon dioxide forms a protective atmosphere to keep oxygen away. Always close up your bag or canister of coffee to keep out oxygen and keep in carbon dioxide.
Grinding coffee will release up to half of the carbon dioxide within a few minutes and the grind will slowly lose the carbon dioxide over the course of days. Course ground coffee will lose the least carbon dioxide and fine ground the most. Keeping the bag closed will help prevent further loss.
An issue to be aware of when buying and drinking coffee goes further than the bag. Many coffee plantations are human rights violators, especially in Brazil. Many large suppliers of coffee have purchased coffee grown and picked using slave labor. Although coffee is originally from Africa, it was stolen and imported to South America and Haiti, along with Africans captured to tend it. Native people, particularly the Mayans, were also enslaved to bring us coffee.
This means that besides grinding beans before use & keeping the bag closed, the ideal cup of coffee will be Fair Trade.
This company will let you select country of origin, are Fair Trade, and send you a clip to keep the coffee closed. They also advocate putting coffee in the freezer and I agree. The gases will be lost from the coffee pores much more slowly when cold.
There are plenty more to choose from should you do a search. Like grinding my coffee, paying attention to Fair Trade has not been a priority of mine. However, it will be in the future.
Thanks to this article for information on carbon dioxide in coffee:
Time-Resolved Gravimetric Method To Assess Degassing of Roasted Coffee, Journal of Agricultural and Food Chemistry, 2018, 5293-5300. Corresponding author is Chahan Yeretzian