[Video Guide] Why Your Espresso Tastes Bad (and How to Fix It): 4 Key Tips from Coffee Science

Espresso brewing is a precise science where small details make a big difference. In this guide, we’ll break down the key factors behind great espresso—fresh beans, grind size, puck prep, and temperature—so you can consistently pull smooth, rich, and flavorful shots at home.

Frequently Asked Questions:

Why does my espresso taste sour?
Your espresso is likely under-extracted. Try grinding finer, increasing brew time, or raising your water temperature slightly.

Why is my espresso bitter?
Bitterness comes from over-extraction—grind coarser or reduce your brew time.

What’s the ideal espresso ratio?
Use a 1:2 ratio for dark roasts, 1:2.2 for medium, and 1:3 for light roasts.

How long should a shot of espresso take?
Between 25 and 30 seconds for a balanced extraction.

Do I need an expensive espresso machine?
No. A well-calibrated entry-level machine, fresh beans, and proper technique can produce excellent results.

Many home baristas wonder why their espresso doesn’t taste as good as it does at the café. The answer usually lies in the science of extraction. Espresso isn’t just strong coffee—it’s a method that uses high pressure to push hot water through finely ground beans, creating a concentrated, velvety shot topped with crema.

1. Fresh Beans Matter
Start with freshly roasted coffee. Espresso made with beans older than three weeks loses its aroma and body. However, using beans that are too fresh—roasted less than seven days ago—can be equally problematic because they haven’t finished degassing. The ideal brewing window is 7–21 days after roasting.

2. Nail the Grind Size
Grind consistency can make or break your espresso. Too coarse, and your shot will gush out weak and sour; too fine, and it’ll choke the machine and taste bitter. Aim for a grind slightly finer than table salt. The perfect espresso should yield about 45g of liquid from an 18g dose in roughly 30 seconds. Adjust your grind gradually until you hit that balance.

3. Perfect Your Puck Prep
Even distribution and consistent tamping prevent a common espresso flaw called channeling. This happens when water finds uneven paths through the coffee bed, leading to over- and under-extraction. After dosing your grounds into the portafilter, level them out and tamp with firm, even pressure—around 30 pounds. The goal is a flat, smooth surface that ensures uniform water flow.

4. Temperature and Pressure Control
Espresso extracts best at around 200°F (93°C) and nine bars of pressure. Water that’s too hot will scorch the grounds, while water that’s too cool won’t release the coffee’s full range of flavors. Lighter roasts benefit from slightly higher temperatures, while darker roasts do better slightly cooler.

You don’t need an expensive espresso machine to make great coffee at home. What matters most is understanding how these small details—fresh beans, grind, tamping, and temperature—work together. Master these fundamentals, and you’ll transform bitter, uneven espresso into smooth, café-quality shots every time.

Full Video Transcript:

"Today we’re diving deep into the science behind espresso to uncover exactly why your espresso might not taste great—and, more importantly, how to fix it. I’m going to show you four simple yet effective techniques to get the most out of your espresso machine. On the left, you can see the type of espresso I used to make—the way many of us do at home—and on the right, how I make espresso now. Stick around as we dive into what the new Lizzy is doing differently and how you can replicate these results in your own kitchen.

If you’re new here, my name’s Lizzy, and I’m all about helping you make better coffee at home. So if you want to learn more about that, hit the subscribe button—it really helps us keep making these videos. And for returning viewers, welcome back!

So, what exactly is espresso? It’s not just strong coffee. Espresso is a brewing method that uses high pressure to force hot water through finely ground coffee. This process, which takes about 25 to 35 seconds, produces a concentrated shot of coffee known for its rich flavor and creamy foam called crema. It’s the base for nearly all milk-based drinks like flat whites and cappuccinos.

The key to a great espresso lies in the details, starting with your beans. Are they fresh? Espresso needs freshly roasted beans—ideally used within one to three weeks of roasting. If you’re buying good-quality beans, check the roast date label. Old or improperly stored beans will give you a flat, lifeless espresso. The prime window for brewing is between seven and twenty-one days after roasting. Coffee roasted less than a week ago still needs time to degas, while anything much older starts to lose its aroma and complexity.

Next comes the grind size, where many people go wrong. Espresso requires a fine grind—finer than table salt—but not so fine that it clogs the filter. Too coarse, and the water flows through too quickly, leaving you with sour, under-extracted coffee. Too fine, and you’ll over-extract, resulting in bitterness. The sweet spot produces a rich, balanced shot in about 30 seconds.

Always grind your beans fresh. If you don’t have a grinder, ask your roaster to grind for espresso. A burr grinder is ideal because it produces consistent results and lets you make micro-adjustments. Experiment to “dial in” your espresso: use a 1:2 ratio for dark roasts, 1:2.2 for medium, and 1:3 for light roasts. If your shot runs too quickly, grind finer. If it’s too slow, grind coarser.

Then comes puck preparation—tamping and distribution. Uneven tamping causes “channeling,” where water finds weak spots in the coffee bed, over-extracting some areas and under-extracting others. Distribute your grounds evenly in the portafilter by tapping, shaking, or using a distribution tool. Tamp evenly with about 30 pounds of pressure—enough to compact the grounds but not crush them. A flat, level surface ensures even water flow and consistent flavor.

Now let’s talk brewing. Espresso machines work by pushing hot water through the coffee at high pressure—typically nine bars—at a temperature of around 200°F (93°C). If your water is too hot, the coffee will taste bitter; too cool, and it will taste sour. Lighter roasts generally need slightly hotter water than dark roasts.

A perfect shot takes 25 to 30 seconds. If it’s running too fast, your grind is likely too coarse or your tamp too light. Aim for a steady, honey-like flow with a golden crema on top. You don’t need a luxury espresso machine to achieve this—a good entry-level model paired with fresh beans and solid technique can produce café-quality results.

If you found this video helpful, hit the like button, share it with your fellow coffee lovers, and subscribe for more coffee tips and tricks. See you in the next video!"