How Ground Coffee Loses Its Caffeine Over Time

coffee in a moka pot

If you got a fresh bag of roasted coffee beans, you might be wondering whether you need to portion and store the beans, only grinding what you need. You should never grind an entire batch of beans all at once if you cannot use up the grounds in two weeks because they lose taste over time. But does ground coffee lose caffeine over time as well?

Ground coffee loses caffeine over time, but much slower than it loses flavor, quality of taste, and its signature pH. In other words, bad-tasting coffee will become a greater problem long before lack of potency becomes an issue. To avoid this, you can get coarse grounds from lightly roasted beans.

In this post, you will learn how:

  • Roasting makes caffeine unstable in a bean 
  • Grinding increases surface area, making the contents more reactive
  • Temperature leads to loss of caffeine
  • Humidity and water leads to loss of caffeine

What Preserves Caffeine?

To understand how coffee grounds lose caffeine, you need to learn what keeps caffeine in place in coffee beans, to begin with. From its initial discovery that came with cattle eating the raw beans to the recent obsession with fresh-ground coffee, we have always known that newer grounds are better. But what if the caffeine loss process begins before the grinding itself.

The Bean’s Water Content

The first step that puts the coffee on a potency-loss timer is roasting. That’s because the coffee beans lose 90% of their water in the roasting process. This water acts as a natural preservative, which is why you can technically store unroasted beans forever. 

But once that dehydration occurs, the water content of the air becomes a threat to the beans. This, however, has more to do with the loss of flavor than caffeine. Coffee beans roasted whole lose caffeine too slowly for there to be any cause for concern regarding potency. They lose taste in a relatively shorter period (2 to 3 weeks), which is a different story.

It is handy to remember that internal water locks the caffeine, whereas external water releases it. Even unroasted beans sitting in water will extract some essence, though it would be nominal and barely beyond trace amounts. Since most people deal with roasted beans, you must see water as the enemy in every shape or form because it is a catalyst for potency loss.

How does this help you? While knowing how the bean’s pre-existing water content can preserve caffeine doesn’t help you unless you get to decide when to roast your coffee and can actually store unroasted beans, understanding how water interacts with the bean post-roasting can help you preserve caffeine by opting for dry storage. You can also keep the bean in airtight containers like Keetan Food Jar after knowing that water contains moisture which interacts with coffee beans to induce some caffeine loss.

The Bean’s Surface Area

When a coffee bean exists in nature, it is shielded from the outside world by the “coffee fruit,” which envelopes the bean. Once this flesh is stripped, and the bean is exposed, it is open to interacting with the environment. Still, the bean is relatively inert because of its water content keeping the caffeine stable. 

Once roasted, this shield is missing, but you still have the comfort of a small surface area. The air hits the bean from fewer sides. But when the bean is ground, each powdery particle gets hit from each side by air and the elements. This leads to a quicker loss of taste, cutting the coffee’s freshness lifecycle by 50%. Since roasted beans go taste-stale by three weeks, the grounds reach that point by a maximum of one and a half weeks.

How does this help you? Considering how you cannot make a bean any larger than it is, how does it help you to know the role played by a bean’s surface area in caffeine loss? While you cannot make the bean any bigger, you can decide how small it gets when you grind. 

The information above helps you understand that you can opt for coarse grinds to ensure that they retain their caffeine over a longer period. That said, these grounds will also require longer brewing to release the same amount of caffeine as finer grounds.

Temperature

If you’ve heard about freezing coffee beans, you already have the idea that the cold preserves caffeine. This also explains two seemingly separate phenomena. Firstly, cold brewing takes 48 times longer, and secondly, frozen roasted coffee beans last five times longer than ones sitting in the pantry. 

In both instances, it is the lower temperature that is hindering the loss of caffeine from coffee beans/grounds to water or the surrounding environment. Why is one 48 times longer while the other only five times, though? That’s because, with cold brewing, we’re looking at the time it takes to lose caffeine, while with beans, we’re looking at the time it takes to lose taste and caffeine. 

Moreover, the comparative “normal” differs as well. We’re comparing cold brewing to near-boiling temperature “normal” of traditional brewing methods. On the other hand, freeze-storage of roasted beans is being compared to a room-temperature pantry, which won’t strip coffee of its caffeine as rapidly as boiling water.

How does this help you? It shows you that you can use the relatively cold temperature to your advantage not just in storage but also in roasting. Choosing a light roast means you’re dealing with coffee that hasn’t gone through that extreme a temperature (compared to dark roasts). As a result, it can afford to sit longer at regular temperatures without losing significant amounts of caffeine.

Aside from the roasting process, knowledge of temperature’s relationship to coffee’s caffeine loss helps you understand the importance of storing coffee in cooler places. This, however, isn’t a game-changer because you probably already know that you must store coffee beans in the cold. What I would add here is that you need to consider the importance of other factors as well.

If you place grounds in a freezer and the container collects moisture from trapped water vapor, you expose the beans to the elements that can lead to potency and taste loss. But since the temperature has the highest impact on the caffeine release process, you can get away with this mistake and still have relatively potent coffee. Dryness is only secondary to temperature but is still quite important, taking priority over the surface area. 

Dry grounds and soaked roasted beans at room temperature will lose potency at different rates, with the grounds being good for a whole week while the beans being less potent within 24 hours. Finally, you should also remember that coffee doesn’t stop oxidizing or losing taste and potency after you brew it. Therefore, using an airtight coffee tumbler like Veken Coffee Canister helps keep the taste loss at a minimum when you take your coffee on the go.

How to Memorize Coffee Storage Priorities

Now that you know how coffee loses its caffeine, it is time to memorize the factors in order, so you don’t overlook any. Ideally, you would like to have all the factors working in your favor, but sometimes there are trade-offs, and knowing what to prioritize can help you extend your coffee’s lifespan. The following memory device helps you remember the order of impact the different factors have on the coffee.

Imagine a tall dark gentleman in a tailor-made suit sipping coffee at an upscale cafe. This individual will help you preserve your coffee’s essence. How? Simply remember the words Tall, Dark, and Sober. Or Talk, Dark, and Suited-up. These words from the acronym TDS, which can be turned into Temperature, Dryness, and Surface area.

  • Temperature: Always opt for the beans that have gone through lighter roasting, and store them in a colder place. Even after brewing your cup, make sure you store it in an airtight flask to preserve its temperature. 
  • Dryness: Make sure that your roasted beans remain dry by minimizing contact with room temperature air (which contains moisture) and storing them in airtight containers like Apextone Coffee Canister.
  • Surface area: Opt for whole beans for long-term storage, coarse grind for medium-term storage, and fine grind only if you can finish the batch within a week.

Other factors that affect your coffee’s lifespan:

When it comes to storing coffee, you’re not trying to preserve just its potency but also its taste and consumability. Here are some factors that can impact your coffee adversely.

Light

People don’t usually put coffee grounds in the sun because of general caution surrounding high temperatures and roasted coffee. However, they don’t realize the extent to which coffee gets affected by light itself. We can tell light and heat apart because shining one’s mobile phone flashlight on the back of one’s hand is a different experience compared to placing that hand on a hot plate. 

But that’s only because our nerves have different degrees of sensitivity. Coffee beans are much more sensitive to light, even though they might not feel its heat. The phenomenon where light breaks down the contents of a roasted bean is called photodegradation, and it happens even with a kitchen lamp.

This factor affects coffee’s taste the most after roasting, and the only reason it isn’t atop the TDS priority chart is that it doesn’t affect caffeine as much as temperature, dryness, and surface area. But all of these factors get affected by the presence of intense light. For instance, the harsher the sunlight, the hotter the weather, which means coffee loses its contents to the environment due to high temperatures.

While the surface area doesn’t get affected by light, light does have more of an impact the finer your coffee is ground because there are more surfaces for the light to hit. Finally, dryness is affected primarily by how light/heat affects water content in the environment. If you live in an area with a large body of water nearby, intense light can make the environment more humid. In contrast, certain landlocked states have dry weather regardless of the heat.

How does this help you? Knowing that it’s not just heat that messes with your coffee grounds but also light means you’ll opt for an opaque container. You will also avoid light’s indirect impact by paying attention to humidity and avoid opening the same container multiple times. That brings us to the other factor that affects coffee’s taste.

Opening the Container Multiple Times

If you grind a large quantity of coffee at once, you’ve already committed the first sin of coffee storage, but this mistake never occurs in a vacuum because it is almost always followed by pouring the grounds into a single, usually large, container. 

The issue with large containers is that you cannot win regardless of where you put them. If you put one in the kitchen, the room temperature and kitchen environment pounce on it. So TDS would suggest popping the container in the freezer. That should work. Right? Wrong.

As you start using up coffee grounds, the empty space in the container starts to increase. Guess what fills that space? Air alongside its humidity. Putting the container back in the freezer is like creating a mini rain experiment in your coffee jar. The air condenses and interacts with your coffee grounds’ top layer. This messes with the coffee’s flavor and taste, if not its caffeine content.

How does this help you? Knowing this means you’ll use multiple containers and store most of the grounds in a mini jar filled to the brim. This way, air wouldn’t have a chance to condense and interact with the coffee, nor will they be repeatedly exposed to the environment.

Dirty Kitchen Environment

You can have five air conditioners in the room and an equal number of dehumidifiers, but if you store your coffee next to molding bread, you cannot consume it without ending up learning the name of your local stomach pumping specialist. 

Coffee is like a movie tough guy antihero who has a softcore; he is seen by others as bulletproof and emotionless, which is why they mistreat him. While coffee is bitten and is seen as practically non-perishable, it can get stale and unhealthy.

You may not be able to extend coffee’s longevity beyond its maximum viable consumption date, but you can cut it short by storing it in dirty conditions. Coffee can absorb scents and odors just as much as objects can absorb its aroma. To make sure your storage space and general coffee consumption environment are safe, follow these best practices.

Coffee Storage Best Practices

  • Keep your coffee jars away from meat, bread, and open containers or milk – These products can accumulate bacteria, fungus, and kitchen mold, which is invisible at the stage of its propagation. 
  • Keep the grounds away from the cooking station – As common as having a coffee jar next to the stove is, it is probably the worst place to have your roasted coffee.
  • Keep the grounds in a non-screw jar/container – Screw-top containers act as mini-grinders accumulating coffee grounds in the lid. These grounds get finer each time you screw the top shut. The best kind of container is an airtight one that doesn’t require screwing the lid shut.

Final Thoughts

Coffee grounds lose caffeine slowly and taste rapidly if you mishandle their storage. Never storage ground coffee for over three weeks, and know the following to preserve its profile and potency throughout these weeks:

  • Temperature affects caffeine content. 
  • Interaction with water, humidity, and oxygen adversely impacts the grounds’ caffeine content.
  • Caffeine loss increases with a finer grind, as does the beans’ surface area.
  • Caffeine is truly secure only in the unroasted bean inside the coffee fruit.

Sources

Tim S.

Tim loves roasting, brewing, and experimenting with coffee. After years of perfecting this craft, working as a barista, and owning a small coffee service in college, he has decided to share his knowledge with the world.

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