Everyone has an opinion about coffee.
Sometimes two.
Sometimes very firm ones.
Some people say it dehydrates you. Others that it depletes magnesium. Someone heard it raises blood pressure, and someone else is convinced that a decent cup is only possible at a café - ideally from a barista with a beard and a sleeve tattoo.
At JAVA we hear all of this regularly. So we took five of the most common coffee myths and looked at what the research actually says. No scaremongering, no preaching, no "well, actually." Just the facts - and a few practical takeaways.
Myth 1: Coffee dehydrates you
Verdict: myth — at moderate intake, coffee does not dehydrate you.
This one keeps coming back, usually paired with: "I drink coffee, but I have to make up for it with extra water." Where does it come from? Caffeine does have a mild diuretic effect — that part is true. The problem is that most people draw conclusions that go much further than the evidence supports.
Research shows that a cup of coffee is, first and foremost, water — its fluid balance is positive, not negative. A study published in PLOS ONE (peer-reviewed, indexed in PubMed) found that moderate coffee consumption, up to four cups a day, does not lead to dehydration in healthy adults (Killer et al., University of Birmingham, 2014). What's more, regular coffee drinkers adapt to caffeine over time, and the diuretic effect gradually decreases.
When does it look different? The diuretic effect is more noticeable if you drink coffee only occasionally, consume a large amount of caffeine at once, or are particularly sensitive to it. If you drink coffee every day — your body has long since adjusted.
Staying hydrated throughout the day is a good habit regardless of coffee. But you don't need to treat every cup as a debt to pay back with water.
Myth 2: Coffee depletes magnesium
Verdict: partly true, but significantly overstated.
This myth sounds very health-conscious, which is exactly why it sticks. It feels credible and it's hard to challenge in casual conversation.
The reality is more nuanced. Caffeine can temporarily increase magnesium excretion in urine — research does show this. But at moderate coffee intake and with a reasonably balanced diet, this effect does not lead to clinically meaningful deficiencies. Coffee also contains trace amounts of magnesium itself, which partially offsets the mechanism.
There is one situation worth keeping in mind: if you drink very large amounts of coffee, follow a diet low in magnesium, and are experiencing symptoms of deficiency — muscle cramps, fatigue, disrupted sleep — coffee may be one contributing factor. Not the main culprit, but part of the picture.
If you drink three or four cups of good Arabica a day and eat a varied diet, coffee is not the problem here.
Myth 3: Coffee causes high blood pressure
Verdict: myth — in regular drinkers, coffee does not cause chronic hypertension.
This myth comes up most often from people who have been drinking coffee for years and quietly wonder whether they're doing themselves harm.
Caffeine does cause a short-term rise in blood pressure — that is well documented. The effect appears around 30 minutes after drinking coffee and passes within 1–3 hours. In regular coffee drinkers, however, the body adapts to this mechanism and the response becomes significantly weaker or disappears altogether. Large observational studies, including meta-analysis reviews, have found no link between moderate coffee consumption and the development of chronic hypertension in healthy people.
When should you be more careful? Occasional drinkers may notice a more pronounced spike after each cup. People with an existing diagnosis of hypertension, heart rhythm issues, or high caffeine sensitivity should discuss their coffee intake with a doctor — not because coffee is harmful, but because individual context matters.
Read also: Is coffee healthy? We confirm the facts and debunk the myths
Myth 4: All coffee has the same amount of caffeine
Verdict: myth — caffeine content varies significantly depending on the bean, roast level, and brewing method.
"Coffee is coffee" — we hear that a lot. But the difference in caffeine between a shot of dark-roast espresso and a large cup of lightly roasted filter coffee can be over 100 mg. That is not a minor detail.
Three variables determine how much caffeine actually ends up in your cup:
Bean variety. Arabica contains around 1.2–1.5% caffeine by dry weight. Robusta contains 2.2–2.7% — nearly twice as much. JAVA Coffee works exclusively with Arabica, which naturally delivers a gentler caffeine experience.
Roast level. Counter to what most people assume, darker roasted beans contain slightly less caffeine than lighter ones — caffeine partially breaks down during the longer roasting process. A dark espresso roast is not automatically stronger in caffeine than a lightly roasted filter coffee.
Brewing method. This is where the differences per cup are greatest:
| Method | Serving size | Caffeine (approx.) |
|---|---|---|
| Espresso | 30 ml / 1 oz | 60–80 mg |
| Filter / pour-over | 240 ml / 8 oz | 120–180 mg |
| Moka pot | 60 ml / 2 oz | 100–130 mg |
| Cold brew | 240 ml / 8 oz | 150–200 mg |
| Instant coffee | 240 ml / 8 oz | 60–100 mg |
So one coffee wakes you up properly, another is simply a pleasant ritual. That is perfectly normal — and entirely predictable once you know what affects it.
Read also: How long does caffeine last? A guide to coffee and caffeine
Myth 5: Only a barista can make great coffee
Verdict: myth — with good beans and basic consistency, café-quality coffee is achievable at home.
Ten or fifteen years ago, this was almost believable. Home equipment was either expensive or mediocre. Good whole-bean coffee was hard to find. Knowledge about brewing was locked behind the counter.
That has changed. A decent burr grinder for home use no longer costs a fortune. Drippers, AeroPresses, Chemexes — straightforward to use and easy to repeat. Specialty coffee is available online, freshly roasted, with full origin descriptions. And there are hundreds of reliable brewing resources to learn from.
The gap between home coffee and café coffee increasingly comes down to three things: bean quality, fresh grinding, and basic process consistency. The address of the venue is not part of the equation.
The bean matters more than the equipment. A good, freshly roasted Arabica will forgive imperfect technique. Poor beans won't — not even in the hands of the best barista. After the bean itself, a good grinder is the next change you will actually taste in the cup.
How we see it at JAVA
At JAVA we work with coffee every day. We talk to people, drink coffee with customers, listen to questions and doubts. And we know one thing: coffee myths don't come from ignorance. They come from oversimplification.
We're not trying to correct anyone or lecture. We just want to take the unnecessary pressure off coffee.
Good coffee doesn't need to be stressful, require expert knowledge, or fit anyone's definition of "correct."
It just needs to taste good.
Good coffee is a human right.
And knowledge about coffee shouldn't be harder than the coffee itself.
Frequently asked questions about coffee myths
Does coffee dehydrate you?
No — at moderate intake, coffee does not dehydrate you. A cup of coffee is mostly water, and its net fluid balance is positive. The diuretic effect of caffeine is mild and weakens in regular drinkers. Staying hydrated is a good habit regardless of coffee, but you don't need to compensate for every cup you drink.
Does coffee deplete magnesium?
Caffeine can temporarily increase magnesium excretion, but at moderate coffee intake and with a balanced diet, this does not lead to significant deficiencies. The issue is more likely to arise with very high caffeine intake combined with a diet already low in magnesium — in that case, it's worth looking at the overall diet, not just the coffee.
Does coffee raise blood pressure?
It causes a short-term rise in blood pressure — an effect that lasts 1–3 hours and weakens in regular drinkers. Moderate coffee consumption has not been shown to cause chronic hypertension in healthy people. Those with existing cardiovascular conditions should discuss their intake with a doctor.
How much caffeine does espresso have compared to filter coffee?
A shot of espresso (30 ml) contains around 60–80 mg of caffeine. A large filter coffee (240 ml) contains 120–180 mg. A small espresso actually has less caffeine than a cup of filter coffee, despite tasting more intense. Caffeine content depends on the bean variety, roast level, and brewing method.
Can you make café-quality coffee at home?
Yes — with good beans, fresh grinding, and basic process consistency, café-quality coffee is achievable at home today. The biggest difference is made by bean quality and the grinder, not the location or a barista title.
Sources
- Killer S.C. et al., No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population, PLOS ONE, 2014.
- Ferrini R.L., Barrett-Connor E., Caffeine intake and endogenous sex steroid levels in postmenopausal women, American Journal of Epidemiology, 1996; and review: Hallström H. et al., Coffee, tea and bone health, Proceedings of the Nutrition Society, 2006 — in the context of mineral excretion with caffeine intake.
- Palatini P. et al., Coffee consumption and risk of hypertension: A meta-analysis, European Journal of Nutrition, 2016.
- EFSA, Scientific Opinion on the Safety of Caffeine, 2015 — data on caffeine content across beverage types.
