A Simple Test on Freshness You Can Do at Home With Your Coffee
Discover whether that bag of coffee you bought at your local grocery store will be a dud or not even before brewing it for a taste test.
Gas in My Coffee
Last week I had a pleasant coffee experience. I opened a new bag of my favorite go-to roasted coffee bean, brewed a cup, and found that it tasted uncommonly better than usual. I then took the bag and emptied it into a mason jar with a sealed lid and stored it in a dark space in a cabinet. The next morning, when I opened the jar to grind a new cup’s worth of coffee, I was greeted with a hiss of escaping gas and the tell-tale pop of the mason lid. This told me that my coffee beans from my new bag were actually relatively fresh and were still releasing carbon dioxide. I was pleasantly surprised.
The majority of the time, I buy my coffee beans already roasted and sold through my neighborhood Kroger grocery store. While the brands I choose are typically categorized as “craft coffee” brands—meaning that they are a cut above lower-quality commodity coffee brands—I am suspicious by nature and have found that any one brand of bag over the year can yield inconsistent taste results.
Presumably this is due in large part to just how old the whole beans are by the time they have made it from the roaster to the shelf in a store. The longer the period of time, the older and less fresh the beans are…and hence, the effect on taste.
Moreover, there are other reasons too, such as a batch of beans coming from subpar growing conditions and regions, faulty or subpar processing, or a lower quality bean chosen to help keep costs within a budget. But for now, we can consider time as our most likely culprit on bean taste quality when buying from a local grocer.
What’s With the Gas?
When coffee beans are roasted, and for some time after, carbon dioxide is released from chemical reactions occurring in the bean. Typically, after a roast, the beans are allowed to degas anywhere from a few days to a few weeks depending on the bean itself and how the bean is to be eventually brewed.
At its simplest, brewing beans immediately after roasting is typically not done because the carbon dioxide coming off the freshly roasted beans will affect the pulling of the coffee extract and its flavor—especially when making an espresso. However, waiting too long after roasting can result in a coffee that falls flat.
If you take a close look at a bag of craft coffee, you will notice a small one-way valve on the side of the bag. This valve is a way to maintain a vacuum in the bagged bean to help it retain its flavor while at the same time allowing excess carbon dioxide to escape from the bag as it slowly degasses. Presumably, coffee roasters for craft brands have it worked out at just how much degassing a freshly roasted bean needs before packaging, balanced with the amount of degassing that occurs while on the market at your grocer, and thereby its shelf life.
In other words, some degassing still in progress yields a better taste—such as I recently experienced in my new bag of go-to craft coffee bean—while a completely degassed (old) batch of beans yields less of the desired flavor.
Simple Test of Freshness
One of my habits is that I typically carry three different sources of coffee beans at any one time in my kitchen to supply my daily coffee drinking. I prefer variety, because for me it’s really about the pleasure of each sip and having a range on hand that keeps the experience fresh; and, matches my mood at a particular time of day.
Here’s the thing with keeping multiple bags. Once you open a bag by breaking its seal, no amount of careful folding of the opened edge afterward is going to achieve a good seal. My habit is to pour the new bag of beans into a mason jar with an inner rubber lid seal to store the beans as I use them. But, only with beans that are jar-worthy, i.e. those that I find are still degassing. Those that are already well on their way of having met their shelf life, I leave in their original bag and close as best as I can, and make note to use this one up quicker than the jarred bags.
So, how do I know if the beans are still degassing? One way is to give the unopened bag a squeeze test to feel if there is any pressure within the bag. If the beans are still degassing, but not at a pressure built up enough to force its way out through the bag valve—it’s a good sign. If the bag collapses flat upon squeezing, it probably had a leak somewhere and is likely totally degassed and gone bad.
A surer way, though, is to open the coffee bag, pour a sample of beans to nearly full in one of those small zipper lock snack baggies, and squeeze the air out as best as you can while closing the seal. Pour the remaining beans from the opened bag (but save the bag) temporarily into a jar just in case it proves to be a good bean. Place both in a dark spot in a cabinet and wait until the next day. If the beans are still degassing, you can tell by the gas pressure built up in the snack baggie. If the beans do not show any gas buildup, then you can empty the jarred beans back into its original bag, knowing that this is a batch to use up relatively soon.
In the next article, we will take a look at how to read the label on your bagged coffee beans and what it means to you and your next cup of coffee.
Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Timothy continues writing about science with a focus on the connection between coffee and healthy living. For continual updates about the benefits of coffee on your health, you can also follow Timothy on Twitter at
Image courtesy of Pixabay