Does coffee lose caffeine when reheated?

Does a trip to the microwave see your coffee lose its caffeine?

So, you’ve made your lovely morning cup. Then something happens. Maybe the phone rings or the dog barks, or David Beckham pops round for a drink (perhaps not).

Then you come back to a lovely mug of… cold coffee. Yippee. So off to the microwave it is.

But when you take a sip of your reheated coffee, it tastes a bit different. A touch more bitter. What does this mean? That reheated coffee has more caffeine?

Let’s find out.

What is caffeine?

Before we get to the why, let’s answer the what: what the HECK is caffeine??

Caffeine is a natural, water-soluble alkaloid found in over 60 plant species. Most of the caffeine we eat and drink comes from coffee, but you can also find it in tea, chocolate, energy drinks and fizzy pop.

Caffeine is totally fine (pretty healthy, actually) when enjoyed in moderation. It gives our brain function a boost, aids weight loss and gets us out of bed when the duvet practically has a magnetic pull.

One arabica coffee bean contains 1.9 milligrams of caffeine. This means that each gram of coffee contains, on average, 12 milligrams of caffeine. And a cup? A filter cup gives you around 140mg of caffeine, while a single espresso has 63mg of our favourite brain booster.

But does this change when we start reheating coffee?

Does coffee lose caffeine when reheated?

The answer is no; caffeine doesn’t go walkabouts if we start to reheat it.

Caffeine is a stable compound. It is produced in the bean when the coffee seed matures, and it likes your coffee rather a lot.

Reheating coffee at home doesn’t alter the number of caffeine molecules it contains. This makes sense when you remember that most of a bean’s caffeine survives the high temperatures in the roaster (we’re talking 216°C here). These scorching temperatures don’t scare the caffeine away, so the 100°C or so of your hot water isn’t going to make much difference! Like we said, caffeine loves your cup just too much!

You can take the caffeine out of coffee beans, of course. But only via a special decaffeination process. This creates (drumroll…) lovely decaf coffee!

Caffeine extraction

Okay, you’re telling me there’s minimal chance of coffee losing caffeine when reheated. So why does warmed-up coffee taste so different?

It’s all down to the rate at which compounds in your coffee extract. Brewing coffee is a super-precise process which, when spot-on, extracts just the right amount of each compound. Sweetness, acidity, bitterness – they’ll all be there in perfect harmony when you brew your coffee just right.

Different compounds extract at different rates:

• Acids and fats extract first – acids contribute to floral, fruity flavours
• Sugars extract next – these bring balancing, sweet flavours
• Caffeine wiggles its way out last – this brings bitterness

Why does coffee taste different when reheated?

Reheating coffee is like brewing it again. You are adding more heat, which makes more of the compounds extract.

Remember that flavour and aroma compounds (acidity, sweetness and their flavourful chums) extract first. So, when you reheat coffee, you disrupt the lovely balance you created when you first brewed. You ‘overcook’ it – a bit like making a cake and sticking it back in the oven after it’s cooled. Particles evaporate and fade, and your reheated coffee tastes flat and smells… of not-really-anything.

But the amount of caffeine hasn’t changed. The caffeine concentration in your cup might even be a bit higher. This is because some of the water particles evaporate when you reheat, leaving a little less liquid in your cup.

So bring them together: a little less water, a few fewer nice flavour compounds, the same amount of caffeine. The result? A reheated cup that tastes a bit more bitter. But hasn’t lost any caffeine.

Is reheating coffee safe?

Yup. We think you’re a lovely lot, so we’re not going to tell you to do something that’ll give you an icky tum.

Reheating coffee is entirely safe, so you can sleep happy if you want to keep reheating your gone-cold cups.

Just be careful if your coffee contains milk or cream. We’d steer clear from reheating coffee with milk in it if it’s been out of the fridge for more than two hours. Just to be on the safe side.

Can I reheat coffee in the microwave? In the oven?

What’s the best way to reheat coffee? Oven? Microwave? Deep fry (nahhh)?

The oven is generally a no-go – especially if you want a cup with the same amount of caffeine. This is because oven temperatures are high (pretty similar to our coffee roaster), so can start to roast out some of the caffeine in your cup.

The answer’s not as clear-cut when it comes to microwave vs stove. Microwaves are best for flavour preservation. Why? Because they reheat the coffee more quickly, which leaves less time for the volatile compounds to escape. But then some say low and slow on the stove is the way to go (because it’s gentler). Why not try both and see which your taste buds like best?

Are you storing coffee correctly? Not if you’re putting it in the fridge…

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