Caffeine fix: how much caffeine is in used coffee grounds?
Can you still get your caffeine fix from the brown sludge left in the bottom of your brewer? Let’s find out…
What the heck is caffeine?
The thing that gets you out of bed? Your post-workout pick-me-up?
Caffeine is key (like KEY, key), but what actually is it? What would you get if you said, ‘hey, coffee roaster, give me some caffeine’?
A white powdery substance, that’s what. Unlike most of the other compounds in coffee, caffeine can be extracted to form a solid chemical. Caffeine is a water-soluble alkaloid occurring naturally in over 60 plant species. Plants use caffeine to repel pests, while we mainly consume it in the forms of tea, coffee, chocolate and energy drinks to boost our brain function. Caffeine is popular worldwide – it takes the top spot as the world’s most widely consumed psychoactive substance.
There’s absolutely nothing wrong with consuming caffeine in moderate amounts. It’s even been found to help diabetics and heart disease sufferers, and can enhance memory. Now that’s something to remember…
How much caffeine is in coffee beans?
This is a tricky one to answer because lots of little factors play their part. Let’s keep things simple and start with a single arabica coffee bean (aww…). On average, this little fella contains 1.9 milligrams of caffeine. Robusta coffee (the bitter stuff) contains quite a bit more; one robusta bean has approximately 2.9 milligrams of caffeine.
We rarely deal in individual coffee beans, so the next question is this: how much caffeine is there in one gram of coffee? Arabica coffee has a caffeine content of 12 milligrams per gram of coffee. For robusta, it’s about 27 milligrams.
We only roast quality arabica beans at Two Chimps, but before you put a grumpy face on and think we’re being stingy on the caffeine, give us a moment to explain why robusta contain so much caffeine. High altitudes give better quality coffee, and this is where arabica plants normally grow. There are fewer pests here, which is why arabica coffee plants contain less caffeine. Robusta beans grow at lower altitudes, where there are more pests, and have adapted to contain more insect-repelling caffeine. This is one of the reasons why robusta coffee tastes so bitter – it’s got a helluva lot of caffeine!
How about the coffee I drink? Does brewing make a difference?
Let’s check out those little factors we mentioned before – all the other bits and bobs that affect how much caffeine your coffee contains.
The average mug of filter coffee contains 140mg of caffeine. But this is just filter coffee – the brew method you use can alter the amount of caffeine in your cup. It’s largely down to the length of each brew time. Caffeine is water-soluble (it dissolves in water), which means that brew methods with longer brew times give a cup buzzing with caffeine. Why? Because there is more time for the ground coffee to extract into the water. Coffee lovers will know that other factors also impact the extraction rate (hello, grind size), so these should also be kept in mind.
All these factors mean that different brew methods give you coffee with different amounts of caffeine. If you took a 30ml sample of espresso, for instance, you’d find about 126mg of caffeine. A same-sized sample of stovetop coffee would give you 65.7mg, while a 30ml sip of cafetiere coffee will give you a 22.3mg caffeine fix. And milky coffees? Your latte or cappuccino contains the same amount of caffeine as the single or double shot the barista used, as milk contains zilch caffeine.
How much caffeine is in used coffee grounds?
Different coffees all contain different amounts of caffeine, which means that the grounds left behind all contain varying measures, too. Used coffee grounds contain less caffeine than unbrewed grounds or whole beans because some of the caffeine dissolves into the water during the extraction. Compounds (flavour, aroma etc.) all extract at different rates, with caffeine being one of the last to wiggle its way out. Remember what we said about brew times being important? Longer brew times give more time for more caffeine to extract. Just watch out, because if longer slips into too long, your lovely coffee will over-extract and give you a bitter taste.
But let’s get back to those used grounds. How much caffeine do you contain, oh lumpy brown sludge? Specific is impossible, but we can give you a ballpark figure. On average, used coffee grounds contain between 3.59 and 8.09 milligrams of caffeine per gram. Flick back to the top of this article and you’ll see that this is quite a bit less than the 12 milligrams of caffeine per gram of fresh ground coffee. Where has it all gone? Into that lucky first mug!
Can I use coffee grounds more than once?
We’re cheerleaders of the waste not, want not approach, but not when it comes to used ground coffee. Coffee made with second-hand grounds will taste flat and flavourless. Scroll back up again, but to the bit about rates of extraction this time. Flavour and aroma compounds extract first and are largely used up in that awesome first brew. So the one made with used grounds will taste a bit, well, drab. It might also taste overly bitter because used grounds still contain caffeine which will continue to extract. Great news if you want a cup that’s all caffeine and no flavour but, as you’re reading this, I’m guessing you’re not part of that pack. You’re part of #teamtaste, and we’re not keen on reusing coffee grounds unless we really need to!
Don’t put used grounds back in your mug – put them on the garden instead!
What’s the best sort of caffeine fix? Speciality coffee! Get yours now!
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