If you’re a frequent coffee drinker like myself and make a pot a day, you probably go through pot after pot of used coffee grounds daily. This always seems like such a waste as the grounds just end up in the trash bin, so I thought I’d look into whether or not you can reuse coffee grounds.
It turns out, the coarseness of the grounds, their small but residual caffeine content, and their nutrients still offer lots of potential uses beyond making coffee. While you can brew a very weak, second cup with them, they are better used around the house for things like fertilizer, skin exfoliant, and bug repellant.
Let’s take a look at some outside, inside, and personal uses for reused coffee grounds.
How Long Do Used Coffee Grounds Last?
If you properly dry and store your used coffee grounds, they can last up to 2-years [1]. They must be stored in a dry, dark place that is at room temperature and in airtight containers to prevent humidity. Use items like airtight plastic containers, glass jars, or vacuum-sealed bags.
If your coffee grounds aren’t properly dried, they can create problems with regards to foul smells, unappealing colors, and create an environment for fungi, mold, and bacteria to grow and spread. This can become dangerous to one’s health.
Is It Bad to Reuse Old Coffee Grounds?
Not if they are prepared properly. This can either mean reusing them to make a second cup right away or drying them out for other uses around the house. Ground coffee does not expire like other household food items and won’t make you sick unless stored incorrectly.
How Much Caffeine Is Left in Used Coffee Grounds?
If you don’t want to go through the trouble of drying your used coffee beans to reuse them later, you can make a second cup of coffee with them but their caffeine content is going to be low. According to the University of Navarra, spent coffee grounds contain 3.59 to 8.09 milligrams of caffeine per gram of used coffee grounds [2].
When compared to unused coffee grounds, which have 12 milligrams of caffeine per gram for the Arabica bean and 27 milligrams of caffeine per gram for the Robusta [3], the caffeine amount is minimal. This means you aren’t going to get a very good second brew from your used beans.
Uses for the Caffeine Content Left in Used Coffee Grounds
However, you can use the residual caffeine amount as an insect repellant. The caffeine and other compounds found in the used beans act as a natural pesticide, as it causes an insect’s nervous system to stop producing essential enzymes [4]. When this occurs, the insect experiences paralysis and death.
When used beans are applied topically to the skin, the antioxidants of the caffeine can help protect the dermal layers from sun damage (photoaging). It significantly reduces UVB-induced thymine dimer formation as well as sunburn lesions, acting as a natural sunscreen [5].
Other uses that benefit specifically from the unused caffeine content include an increase in blood flow to the skin which may reduce the appearance of cellulite, dark circles, and puffiness under the eyes.
Can You Reuse Coffee Grounds in a French Press?
If you enjoy using the French Press as your brewing method, you may be wondering if you can reuse your coffee grounds for a second cup. The answer here is that you can, but you need to reuse them within 15-minutes. Ideally, you want to reuse them immediately. The longer you wait to reuse them, the more bitter your next steep will be.
An important note for those that do try this, do not expect your second cup to be very flavorful. Most of the flavor is drawn out in the initial brew, leaving little leftover for any subsequent batches. This is even true if you use a very bold tasting coffee the first time around.
What Other Uses Do Used Coffee Grounds Have?
Coffee grounds have a whole range of uses beyond brewing your favorite cup of joe. This includes the following.
- Homemade Fertilizer. Coffee grounds have a lot of the minerals necessary for plants to grow healthy and strong, such as nitrogen, calcium, iron, potassium, magnesium, phosphorus, and chromium. Not only does this unique chemical makeup make coffee grounds an excellent fertilizer, but they also attract worms, making them even better for outdoor gardens. All you have to do is sprinkle the grounds around your plants and water them like you normally would.
- In Compost. If you’re the patient type or don’t have an immediate need for fertilizer, you can make your coffee grounds into compost. Compost is excellent for any garden, as it helps soil retain water and enriches it with nutrients. Making a mixture of 40% coffee grounds and 60% kitchen and yard waste will yield a compost that is both high quality and low on greenhouse gas emissions.
- Neutralize Odors. Old coffee grounds are great for absorbing strong odors. You can use them in your garbage by placing them into a mesh-like bag (think panty-hose) and then hanging them inside the lid of the trash can.
You can also use them in your refrigerator to deodorize it. While some people use baking soda, the coffee grounds have a stronger absorption rate and can make your fridge smell wonderful. Get a cheesecloth piece, fill it with dry grounds, and place it on a shelf in your fridge.
If you like to cook with a lot of garlic or onion, you are aware of just how strong your hands smell of it afterwards. You can eliminate this by wetting your hands and scrubbing a small amount of coffee grounds on them. Rinse with cool water,
- Natural Cleaning Scrub. You can use both wet and dry old coffee beans to effectively clean out pots and pans that have hard to remove food particles. Toss the grounds onto the surface and scrub with a little bit of warm water. This can be done with extremely dirty kitchen countertops too.
- Exfoliate Skin. Don’t worry about buying the store brand exfoliant any longer. You can use your old coffee grounds as a face and body scrub to get rid of dead skin cells. Simply take your old coffee grounds and add a natural oil like coconut with some warm water to them. Apply and rinse with cool water.
- Use as a Natural Dye. Used coffee grounds still bleed their color extremely easily, making them an excellent natural, brown dye. This can be used to darken the color of paper, fabrics, cellophane, easter eggs, and even dark-colored hair, creating a more vintage look. Simply mix the grounds with a bit of water, spread them on the material you want to dye, then wipe or rinse them off when the desired color is achieved.
- Hide Furniture Scratches. If you have dark wood furniture or espresso finishes on some of your larger items, you can use the coffee grounds to hide any scratches. Take a small amount of old, dry grounds and add a tiny amount of warm water to them to make a paste. Rub the paste over the scratch and let it sit for a few minutes. Wipe away with a gentle towel. The coffee will stain the wood, making the scratch less noticeable.
- Tenderize Cuts of Meat. Coffee contains natural acids and enzymes that are particularly effective at breaking down meat fibers, making used coffee grounds a great meat tenderizer. Simply add some to your favorite dry rub and apply it two hours before cooking. You can also make a marinade by re-brewing the coffee grinds, letting them cool, and marinating the meat for 24 hours.
- Drain Cleaner. You can use the gritty texture of the used grounds and their strong scent to help clear out clogged up drains. Simply boil the coffee grounds in hot water, and dump the entire hot mixture down the drain. You can use this to deodorize the drain as well. Feel free to use it on the kitchen sink, bathroom sink, and even the bathtub!
- Grow Mushrooms in a Bucket. Mushrooms are notoriously difficult to grow, as they require very specific conditions and don’t act anything like conventional plants. Used coffee grinds provide the perfect substrate for mushrooms as they contain all the nutrients that mushrooms thrive on, while also being pre-sterilized from being run through boiling water. You can get supplies and instructions from a local gardening store to learn how to grow your own mushrooms.
- Use in Recipes as Food Flavoring. Used coffee grounds work great in a ton of baked good recipes, as they add a rich texture and flavor. Some fantastic recipes that use coffee grounds include leftover espresso ground brownies, peanut butter espresso smoothie, chocolate-coffee scones, Rosemary coffee-orange granola, Irish beef stew with Guinness and coffee, and even espresso overnight oats.
In wrapping it up, you can definitely reuse old coffee grounds, whether that is to make a second cup or to use it around the house for beauty products, environmental uses, and general cleaning.
Just make sure that if you are using them around the house, you properly store and dry your coffee beans first. You can do this by drying them in the oven or drying them in the sun and then storing them in an airtight container.