Taking maximum advantage of any product that we use daily at home, such as coffee, can definitely save us some money or unnecessary trips to the store.
Speaking of which, will reusing coffee grounds provide enough caffeine and be viable for making one last cup, although you’ve already used them once?
I’ve been putting used ground beans to good use as fertilizer in the garden for a while and I’ve been making great scrubs that work miracles for my type of skin.
But could we possibly be making more coffee with those?
I did some research and experimented a bit to be able to answer this question and share my findings with my readers.
My curiosity made me ask myself whether re-brewing coffee grounds will result in a drink that contains any caffeine at all.
Can they be reused for a second round? And would that drink have a satisfying taste?
I’ve also experimented with the cold brew method and illustrated the results.
Is the brewing technique even relevant?
What if you could reuse the grounds from today for your next day morning cup?
Will using the same coffee grounds twice be a good approach to make yourself another serving that’s satisfying enough?
Well, I guess that last question is a bit far-fetched, but bear with me, as the answer may not be so obvious.
Will Reusing Yesterday’s Coffee Grounds for Another Cup of Coffee Work?
When you make your cup of coffee, regardless of the method you use, your coffee grounds go through an extraction process.
Basically, this means that their soluble components get dissolved in the water.
Generally, to get the perfect cup of coffee you need:
- the correct water to coffee ratio*
- perfectly ground coffee beans*
- perfect temperature*
- precise duration of extraction*
* appropriate for the brewing method you use
Furthermore, the type of water you use also plays a vital role in the process of coffee extraction.
You can learn more about the best water for coffee making, by clicking here.
If you get all of those variables right, you will end up with the best, well-balanced cup of coffee in your hands.
I also need to mention the extraction percentage, which tells you what percentage of the used coffee grounds end up dissolved in your pot.
Here’s what happens when you try to reuse coffee grounds for another cup of coffee:
As an example, the ideal extraction yield for espresso is between 18% and 22%.
An under-extraction of 15% or over-extraction of 25% will cause an imbalance in the components and will result in either acidic or a bitter-sweet coffee drink.
Therefore, if you decide to put the coffee grounds through the extraction process for a second time, the beans being used would’ve already lost some of their soluble components during the first extraction.
Since one of the variables, in this case – the coffee grounds, has changed its value and now has less soluble flavors, we would need to adjust all other variables in order to make a balanced cup of coffee.
By tweaking the other variables we could try to achieve similar results and said adjustments may include adding less or more water, increasing the temperature, steeping for longer, etc.
And is all of this worth it? I don’t really think so.
The most common brewing methods we use come with their instructions that take into consideration all of the aforementioned variables to help us end up with the best possible cup of coffee.
If you don’t feel like trying this yourself, I did, and you can see all the results below, in this very article.
I wanted to see and taste the results myself in order to figure things out.
Will the Second Cup Contain Enough Caffeine to Wake You Up?
As we already established, to use coffee grounds for the second time would mean that they’ve already lost some of their key components during the first extraction process.
But is there any caffeine left in them at all, and will it be enough to properly wake you up and increase your productivity?
- According to a study, published on the American Chemical Society website, the majority of the coffee beans have between 10 mg/g and 12 mg/g caffeine concentration.
- An abstract from another study, informs us that caffeine range in spent coffee grounds is between 3.59 mg/g and 8.09 mg/g.
Based on those numbers, here’s a conclusion on how much caffeine we can extract by reusing old coffee grounds:
During the brewing process of coffee we get to extract approximately 50% (this number varies depending on the brewing method and grind size) of the caffeine out of the beans with the first brew.
If you re-brew the used coffee grounds a second time, you will not be able to extract the other 50% of caffeine.
The first extraction changes the value of the components of the coffee grounds.
This means that if you want to extract the same amount of caffeine as with the first brew, you need to make adjustments to the temperature, the extraction duration, the amount of water, etc.
That being said, when trying to reuse the coffee grounds you will also extract some of the slow-dissolving compounds that don’t benefit a cup and ruin its flavor.
If you apply the same brewing method the second time you will still manage to get some caffeine out, but it won’t be as much as the quantity you’re used to.
This means that the coffee you end up with after the second extraction, won’t wake you up, as much as you would expect.
Related post: Why doesn’t coffee affect me?
My coffee grounds re-brewing experiment
What had me thinking about re-brewing coffee grounds is my grandmother.
When we go to her house during the holidays she wakes up really early and makes herself a cup of coffee in her home-grade espresso machine.
A few hours later, one by one, all of the family members wake up and go to the kitchen to have their morning coffee and spend some time together.
As granny doesn’t want to be left out and still be part of the “coffee ritual” (but without overdosing), she pulls another shot with spent coffee with the pressurized portafilter and drinks it with us.
This way she manages to share her coffee ritual with the last person that rolls out of the sheets. So I decided to try this out.
Here on the photo, you can see what the first coffee made with a pressurized portafilter basket looks like:
I reused the grounds in the home espresso machine to make another one, and here you can see the second shot:
As my illustration shows there is a significant difference.
The coffee made with re-brewed coffee grounds is more watery and the flavor is much weaker and unsatisfying.
There is some foam on top, but I can’t seem to settle with the lack of body.
I’d definitely rather have a cup of tea than having this watery drink.
I asked my grandmother why does she drink that.
She laughed and told me she’s just used to the taste.
“I’m not expecting my second-hand espresso to have the same taste as my fresh morning cup.
But I treat it as a post-coffee drink, that I’m used to, and enjoy having during our coffee ritual”.
Anyway, I also tried the coffee I got by pulling a double shot twice in the same cup.
I thought that by doing that and splitting the liquid into two halves I could get 2 decent cups of coffee.
Well, that might work for someone that drinks coffee with sugar and milk. But not for me.
Then I asked myself: What if I don’t utilize the used grounds the same day, but the next one?
So I made a cup of coffee and didn’t empty the pressurized filter basket until the following morning.
When I woke up the next day I checked how the grounds were – well… Let’s say they looked okay but smelled a bit suspicious.
I went ahead and made my drink using them.
Here is what the coffee looked like when made from yesterday’s coffee grounds:
No foam, unpleasant look, and the smell was… unattractive to say the least.
Is it really safe to drink that? I looked up online, whether it is. Here’s what happens if you use coffee grounds that were left overnight:
When reusing coffee grounds to make another coffee the next day you risk ingesting unwanted fungi and bacteria.
These are attracted by the wet grounds and it’s possible that the microorganisms start establishing their colonies in less than 24 hours.
Therefore drinking coffee that’s made from yesterday’s grounds could be potentially dangerous while also having an unpleasant taste.
I guess 24 hours were sufficient for the bacteria and fungi to start doing their job.
So I threw this liquid away and made myself a nice cup of coffee.
Then I thought – what if I dry out the grounds first. This way I make sure the mold doesn’t start building up and then reuse them on the following day?
So I did that.
Here is how the result of re-brewing dried spent coffee grounds from the previous day looks:
As you can clearly see by the results I got that I won’t be doing this next-day-reusing-thing anymore.
So I left the espresso machine behind and continued on with my experiments.
Can Yesterday’s Coffee Grounds Work for the Cold Brew Method?
I love cold brew coffee.
I’ve always wanted to try reusing the coffee grounds for a second batch, as it seems to me that the results would be more fulfilling than the ones above.
I usually let the ground beans steep for 7 to 12 hours (or a maximum of 24 hours, if I can’t filter the grounds earlier) in the fridge.
When the water is saturated with dissolved coffee compounds after the first brew, I separate the coffee grounds from the liquid.
Then I filter with precision and my cold brew concentrate is ready.
My logic tells me that if I were to place more water into the vessel, where the used beans are, stir a bit, and leave the mixture for another 20 to 24 hours, I might end up with a pretty good cold re-brew.
The new unsaturated water would ensure a proper dissolving environment for the soluble components that couldn’t dissolve in the already saturated water from the first brew. Got confused? Me too.
Let’s see what happened:
In the photo on the left side, you can see the coffee, made with the original recipe.
The photo on the right is the one made with the used ground beans.
The second pot is much smaller, that’s why it looks fuller.
Here’s a close-up shot of the color difference between the first batch of cold brew and the one with reused coffee grounds:
As you can see by their colors, the first batch is much darker.
I tried it out – once without added milk, and once with.
Here’s what both cold brew drinks looked like after adding the milk:
My conclusion on reusing your coffee grounds with the cold brew method is:
When it comes to flavor the first batch of cold brew is much richer than the one made with reused coffee grounds.
It is also much stronger in terms of caffeine, compared to the second one.
Nevertheless, the cold re-brew still has some coffee flavor.
Compared to the previous re-brew ground beans experiments I made, it has the best taste, especially if you add milk.
Therefore if you’re reusing coffee grounds with the cold brewing method you will end up with a surprisingly satisfying refreshing drink.
If you have a sweet tooth, add some sugar or syrup to make it even better.
It’s worth noting that I wouldn’t count on the cold re-brewed coffee to wake me up, but I would definitely enjoy it during the day if I feel like having something refreshing.
It might just be me, but I can see myself reusing the cold brew coffee grounds for another batch from time to time.
Not every time, but still… I definitely enjoyed this coffee-ish drink.
Can Reusing Coffee Grounds Work With the French Press or Aeropress Method?
If you have a French press or an Aeropress, reusing the grounds for another cup of coffee is possible as well:
You can try to get better results by soaking the grounds for longer. Nevertheless, the main compounds that make a well-balanced cup of coffee possible have already been dissolved during the first extraction.
The French press and Aeropress methods aren’t an exception to any of the rules of re-brewing. Reuse the coffee grounds shortly after you’ve used them the first time. If you let them sit for longer the results will be much worse.
Again, with these methods, the potency and the quality of the coffee that’s been made with the reused beans will be lower.
Your second French press coffee, made of used coffee grounds, even though a bit watery and with a not-so-satisfying flavor, will contain some caffeine in it.
The caffeine might not be quite enough to banish a food coma after a meal, but the placebo effect will enhance the result.
Related Post: Best French Press Coffee Makers: Reviewed
How can you reuse coffee grounds in other ways?
You can reuse your coffee grounds in much better ways than re-brewing them:
- You can add them to your composting bin.
- If you have a vermicompost – the beneficial worms will love the used ground beans as well.
- You can use them to prevent weeds proliferation.
- If you use commercial exfoliants, you can switch to DIY coffee face and body scrubs and save some money.
- You can use them as a deodorizer in your car or fridge.
- You can make great anti-aging facial masks with them, and also treat dark circles.
- If you want to get rid of cellulite – massages with used coffee grounds under the shower may help you out.
I have been doing most of these for years and I’ve written a detailed article on the ways to reuse coffee grounds.
Visit the link to find further instructions and also find the reasons why spent coffee ground beans have so many applications and work so well.
Reusing the ground beans to make more coffee is possible, but not as rewarding as I would like it to be.
The results I got had me conclude that the only suitable re-brewing option for spent coffee grounds is by reusing them with the cold brew method.
You will likely be satisfied with the results, especially if you drink your coffee sweetened or you add milk.
Nevertheless, caffeine concentration will be significantly lower and you won’t get a strong caffeine kick.
As for other methods such as French press, Aeropress, or espresso re-brewing – I wouldn’t recommend.
But if you think these devices will work well-enough for you, based on everything I told you, that’s totally fine.
Just don’t try to use yesterday’s moldy grounds.
Overall, a second extraction for another cup of coffee isn’t an option that I’d consider in the future.
Still, I’d love to know what you think, so drop me a comment below and share your thoughts and experience on the matter.