Last updated on May 6th, 2025 at 03:41 pm
Estimated reading time: 8 minutes
If you’ve ever wondered why some cups of coffee hit harder than others, you’re not alone—and you’re in the right place. A 2021 study titled “Influence of Various Factors on Caffeine Content in Coffee Brews” by Ewa Olechno, Anna Puścion-Jakubik, Małgorzata Elżbieta Zujko, and Katarzyna Socha, published in the journal Foods, provides the clearest, most detailed breakdown I’ve seen. And today, I’m here to break it down for you in a way that’s much easier to digest.
Whether you’re an espresso junkie, a cold brew devotee, or someone who just loves their morning cup, understanding what really impacts your caffeine intake is fascinating—and might even change how you brew your next cup.
Let’s dive right in.
Introduction: Why This Study Matters
Coffee isn’t just a drink; it’s part of a global culture. It’s loaded with over 1,000 bioactive compounds, but caffeine is the star that keeps most of us coming back.
You might think that brewing a stronger coffee is simply about using more beans or letting it steep longer. Turns out, it’s way more complicated. Everything from bean type, roasting, water temperature, grind size, and even the brewing method dramatically impacts caffeine content.
This study reviews ten years’ worth of research (2010–2020) to figure out exactly how these factors influence the final caffeine levels in your cup.
The Big Picture: Arabica vs. Robusta
First, let’s get something out of the way: Robusta beans have a lot more caffeine than Arabica beans. In fact, Robusta can have up to twice as much caffeine.
| Bean Type | Typical Caffeine Content |
|---|---|
| Arabica | 0.9–1.5% dry weight |
| Robusta | 1.2–2.4% dry weight |
Robusta’s higher caffeine content isn’t random—it’s a defense mechanism against pests and insects. If you’re looking for a real kick, a Robusta-heavy blend might be your best bet.
Factors That Impact Caffeine Content in Coffee Brews
Now, let’s walk through the major factors that the study highlights.
1. Coffee Species
- Arabica generally has less caffeine.
- Robusta usually contains 1.4 to 1.8 times more caffeine than Arabica.
However, not every study agrees 100%. Some brewing methods and coffee origins can shift the typical ratios slightly, but in general, Robusta is your high-caffeine friend.
2. Brewing Time
You might assume that the longer coffee brews, the more caffeine it has.
Not necessarily.
- Espresso brews super quickly (under a minute!) but can still be highly caffeinated because of pressure and fine grind.
- Cold brew can steep for 6–24 hours, but the caffeine concentration isn’t always higher compared to espresso.
Key takeaway: brewing time alone doesn’t predict caffeine content. It’s how you brew that matters more.
3. Water Temperature
This one’s huge.
- Caffeine dissolves better in hot water.
- At 100°C, caffeine is 670 mg/mL soluble.
- At 20°C, it’s only 1.46 mg/mL soluble.
Brewing at high temperatures (90–96°C) extracts more caffeine faster. Cold brew compensates by soaking the grounds for a much longer time.
Bottom line: if you want more caffeine fast, hotter water is your friend.
4. Pressure
Pressure really matters—especially for espresso.
- Espresso machines brew coffee at 7–9 bars of pressure.
- Best caffeine extraction was found at 7 bars at 92°C.
- Interestingly, increasing pressure past 9 bars doesn’t significantly boost caffeine extraction and might even reduce it.
If you want a highly caffeinated espresso, 7 bars of pressure is the sweet spot.
5. Degree of Roasting
You might think dark roast = stronger coffee = more caffeine.
Wrong.
- Caffeine is thermally stable.
- Light, medium, and dark roasted coffees usually have very similar caffeine levels.
- The main changes with roasting are in taste—not caffeine content.
Some studies even found that light roasts have slightly more caffeine, but the difference is pretty minor.
6. Grind Size
Grinding affects caffeine extraction too.
- Finer grind = more surface area = faster caffeine extraction.
- Coarse grind? Longer brewing times needed to get the same kick.
Choosing the right grind size matters depending on your brewing method:
- Espresso: fine grind
- French press: coarse grind
- Pour-over: medium grind
Brewing Methods and Their Caffeine Impact
Different brewing methods lead to wildly different caffeine concentrations:
| Brewing Method | Caffeine Concentration (g/L) |
|---|---|
| Espresso Machine (Portafilter) | Up to 10.3 g/L (Robusta-heavy blend) |
| Cold Brew | Around 1–2 g/L |
| French Press | About 1–1.5 g/L |
| Coffee Percolator | 0.8–1.7 g/L depending on roast and origin |
| Pour Over (Hot Water) | 0.4–1.8 g/L |
Notice how espresso wins in caffeine concentration per volume—but remember, you usually drink a tiny 1–2 oz shot compared to an entire mug of cold brew.
Real-World Example: Highest Caffeine Cup
According to the study:
The highest caffeine content in one serving was found in a brew made with 50g of Robusta coffee poured with 500 mL of cold water (25°C) and then boiled.
That’s a caffeine bomb. Definitely not your everyday cup.
Important Health Considerations
As fun as it is to chase higher caffeine levels, moderation is key.
- EFSA recommends: No more than 400 mg of caffeine per day for healthy adults.
- For pregnant or breastfeeding women, the limit is 200 mg/day.
Overdoing caffeine can lead to:
- Insomnia
- Palpitations
- Anxiety
- Nausea
And don’t forget: your genetics (specifically the CYP1A2 gene) affects how quickly you metabolize caffeine. Some people feel jittery after just one cup, while others can sip coffee all day.
Additional Insights: Summarizing the Study’s Findings
The Foods 2021 studycompiled a mountain of data, so to make it easier for you to digest, I’ve created a few simple tables summarizing the key points.
Table: Caffeine Content by Brewing Method and Bean Type
| Brewing Method | Arabica (g/L) | Robusta (g/L) | Blend (g/L) |
|---|---|---|---|
| Espresso (Portafilter) | 7.9 | 2.5 | 10.3 |
| Cold Brew (French Press) | 1.0–1.9 | — | — |
| Pour Over (Hot Water) | 0.4–1.8 | 0.6–2.5 | 2.5 |
| Coffee Percolator | 0.5–1.7 | 0.8–0.9 | — |
| Filter Machine | 0.5–1.4 | 1.1–1.2 | — |
| Neapolitan Pot | ~1.3 | — | — |
Takeaway: Espresso wins by caffeine concentration—but Robusta in any brew method will give you a bigger hit.
Table: Factors That Most Influence Caffeine Extraction
| Factor | Effect |
|---|---|
| Species | Robusta = up to 2x more caffeine than Arabica |
| Brewing Time | Minor effect unless very short or very long |
| Water Temperature | Major effect: hotter = more caffeine faster |
| Pressure | Major effect up to ~9 bar; minimal beyond |
| Roasting Degree | Minor effect: dark vs. light is negligible |
| Grind Size | Major effect: finer = more caffeine faster |
| Coffee-to-Water Ratio | Huge effect: more coffee = stronger brew |
FAQs: What People Usually Ask About Coffee and Caffeine
Q: Does a darker roast have more caffeine than a lighter roast?
A: Not really. Roasting affects flavor more than caffeine content. Light and dark roasts have nearly the same caffeine per gram of coffee.
Q: Is espresso higher in caffeine than regular coffee?
A: Per ounce, yes—espresso is super concentrated. But per cup, a large brewed coffee often has more total caffeine because it’s a much bigger volume.
Q: Does cold brew have more caffeine?
A: It can, but it depends on your coffee-to-water ratio and steeping time. Typically, cold brew is less concentrated than espresso, but if you drink 16 oz of it, you’re getting a hefty caffeine dose.
Q: How does grind size affect caffeine?
A: Finer grinds extract caffeine faster. That’s why espresso uses very fine grounds and brews in just 25–30 seconds.
Q: What’s the strongest way to brew coffee?
A: Using Robusta beans, finely ground, brewed in an espresso machine at 7 bars of pressure and around 92°C—OR by making a heavy cold brew concentrate with a lot of coffee and a long steep time.
How to Brew Coffee for Maximum Caffeine
Here’s your simple action plan if you want the highest caffeine cup possible:
1. Start with Robusta Beans
- Choose 100% Robusta or a Robusta-heavy blend (95% Robusta / 5% Arabica is ideal).
- Robusta naturally has almost double the caffeine of Arabica.
2. Use a Fine Grind
- Grind your beans very fine—similar to what you’d use for espresso.
- Fine grounds = more surface area = faster and stronger extraction.
3. Maximize Your Coffee-to-Water Ratio
- Use more coffee grounds than usual.
- Example: Instead of the typical 1:15 coffee-to-water ratio, aim for 1:12 or 1:10.
4. Brew With Hot Water
- Ideal water temp: 92°C–96°C.
- Hotter water dissolves caffeine faster.
5. Use Pressure
- Brew in an espresso machine (7–9 bars of pressure).
- If that’s not available, use a Moka pot or AeroPress with added pressure.
6. Brew Quickly but Properly
- Aim for a 25–30 second extraction if using espresso methods.
- If doing cold brew, use a high coffee dose and steep for 18–24 hours.
7. Drink It Fresh
- Freshly brewed coffee has a stronger flavor and fuller extraction of compounds—including caffeine.
Ultimate High-Caffeine Recipe (Example)
| Step | Detail |
|---|---|
| Beans | 95% Robusta blend |
| Grind | Fine |
| Dose | 20 grams of coffee for 30 mL espresso |
| Water Temp | 92°C |
| Pressure | 7 bar |
| Brew Time | 25–30 seconds |
This will result in a tiny, lethal shot of coffee packing well over 200 mg of caffeine in just a few sips.
Final Thoughts
The Foods 2021 study gives us a lot to chew on (or sip on, in this case). There’s no one-size-fits-all rule when it comes to maximizing or minimizing caffeine.
Here’s what you need to remember:
- Bean type matters: Robusta > Arabica for caffeine.
- Brewing method matters: Espresso > Cold Brew > Pour Over, if you’re going by concentration.
- Water temperature and pressure matter: Higher temps and 7–9 bar pressure extract caffeine efficiently.
- Roast level barely matters.
- Grind size matters: finer grind = faster extraction.
Knowing these variables gives you total control over your caffeine intake. Whether you’re seeking the biggest boost or a mellow sip, you now have the science to back your brewing decisions.
