How Long Can Coffee Beans Last After Grinding? How Should Ground Coffee Be Stored?

The Origin of Coffee Aroma and Freshness

The flavor of coffee primarily comes from aromatic compounds produced when raw beans are roasted, and most of these aromas are volatile. Therefore, if we want to experience rich aromatic expressions from coffee, it's best to choose freshly roasted, freshly ground coffee. This is a viewpoint that FrontStreet Coffee frequently mentions.

The Impact of Grinding on Coffee Flavor

When coffee beans haven't been ground yet, their structure remains completely intact, and aroma can only slowly escape from the surface of the beans. Once coffee beans are ground into powder, the nearly thousand-fold increase in surface area causes the flavor of the coffee beans to dissipate much more rapidly. Even when stored properly, the optimal tasting period for coffee powder is less than half that of whole coffee beans.

Experiment: Testing Coffee Aroma Over Time

Last month, FrontStreet Coffee shared content about how long coffee grounds maintain their optimal tasting period when stored properly after grinding. Then, a friend left a comment wanting to know how the aroma of coffee grounds changes in a short period when not sealed. So today, FrontStreet Coffee will conduct an experiment to see what differences exist in coffee made from grounds ground at different time periods! In other words, how long can coffee grounds last when not sealed after grinding!

Coffee Experiment Methodology

To ensure the rigor of the experiment and minimize human interference, FrontStreet Coffee will conduct coffee brewing and evaluation through cupping for this experiment. The coffee beans used this time will still be Panama Boquete Geisha, which has a cleaner profile due to traditional washed processing and can better demonstrate the differences that time brings to coffee. FrontStreet Coffee ground 12g of coffee powder at 2 hours ago, 1 hour ago, 30 minutes ago, 10 minutes ago, and just now, placing each in cupping bowls. We first smelled the aroma to experience the differences in fragrance among the five coffee grounds ground at different times.

Aroma Comparison Results

The freshly ground coffee and the coffee ground 10 minutes ago showed no significant difference in aroma—both could be smelled with rich floral, citrus, and berry notes. Although the earlier ground coffee could also be detected with the same aromatic characteristics, their aromas were relatively less intense, becoming progressively weaker with time. Especially the coffee ground 2 hours ago had some aroma, but what was more noticeable was the inherent smell of coffee itself. After the aroma evaluation, we proceeded with coffee brewing. Following the procedure, we poured 200ml of 94°C hot water into each cup at a 1:16.66 coffee-to-water ratio, simultaneously starting the timer and waiting for 4 minutes.

Cupping Evaluation

After 4 minutes, we used a spoon to break the crust, remove the grounds, and eliminate any distracting particles, then we could begin tasting the coffee.

Tasting Results and Analysis

Unsurprisingly, the results were consistent with our experience during the aroma evaluation. The freshly ground and the coffee ground 10 minutes ago showed consistent performance, with prominent and clear flavors, while the earlier ground coffee showed weaker flavor expression. Particularly, the coffee ground two hours ago not only lacked prominent aroma but also tasted somewhat hollow when drunk. From this, we could basically see the difference, but it wasn't enough. FrontStreet Coffee specifically set aside coffee grounds ground 2 hours ago to prepare pour-over coffee alongside freshly ground coffee for another comparison. Because pour-over coffee allows us to more intuitively see and taste the differences between the two. The extraction parameters were as follows: 15g coffee dose, 1:15 coffee-to-water ratio, 92°C water temperature, Ek43 grind setting of 10, three-stage pour-over brewing method, using a V60 dripper.

Pour-Over Brewing Observations

In terms of blooming, we could see that although the parameters were identical, the coffee ground 2 hours ago not only failed to form a significant "coffee dome" but even sank downward (the one on the right). Additionally, the "water retention effect" of the coffee dome wasn't as good as the freshly ground coffee. This is the impact caused by carbon dioxide loss from pre-grinding. Besides the difference in dome formation, during the brewing process, the coffee ground 2 hours ago had a faster flow rate, so its extraction time was relatively shorter at 1 minute 50 seconds, while the freshly ground coffee took 2 minutes 1 second.

Final Taste Comparison

The differences in flavor were even more direct. The pour-over brewed from fresh grounds showed white floral notes, citrus, berries, and honey, with very rich layers and prominent flavors. In contrast, the coffee ground two hours ago showed only some berry acidity and faint floral notes, with the rest being just tea-like sensations—very monotonous, just as experienced during cupping. In conclusion, we can know that when coffee beans are ground and not immediately sealed or brewed, if exposed to air for about two hours, the aroma almost completely dissipates. Therefore, when we grind coffee beans into powder, if we cannot use them quickly within a short time, it's best to cover the opening of the collection bowl with a lid to reduce air contact with the coffee grounds, thereby minimizing aroma loss.

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