How to fix bitter espresso: A guide to grind size and temperature

There are few things more disappointing in the world of coffee than seeing a beautiful, syrupy espresso shot pull from your machine, only to take a sip and be met with an overwhelming, harsh bitterness. It’s a common frustration for home baristas, turning a promising morning ritual into a wince-inducing experience. This bitterness isn’t a sign of bad beans, but rather a signal that something is off in your brewing process. The culprit is almost always over-extraction, a phenomenon where the water has pulled too many undesirable compounds from the coffee grounds. In this guide, we will demystify this problem and show you how to fix bitter espresso by mastering the two most powerful variables at your disposal: your grind size and your brewing temperature.

Understanding the enemy: What is over-extraction?

Before we can fix the problem, we need to understand it. Making espresso is a process of extraction—using hot, pressurized water to dissolve the flavorful solids and oils from coffee grounds. The goal is to achieve a balanced extraction, where we pull out all the sweet, acidic, and complex flavors without going too far. Bitterness is the classic sign that we’ve gone too far.

Imagine the flavors in coffee being extracted in a sequence:

Acids and fruit notes: These are the first to dissolve. If you stop the extraction too early (under-extraction), your espresso will taste sour and thin.
Sugars and caramels: This is the sweet spot. A balanced shot has a rich body and sweetness from these compounds, balancing out the initial acidity.
Bitter compounds: These are the last to dissolve. When water is in contact with the coffee for too long or is too aggressive (too hot), it starts to break down the very structure of the coffee grounds, releasing harsh, dry, and bitter flavors. This is over-extraction.

So, when you taste that unpleasant bitterness, it simply means your water has spent too much time with the coffee. Our mission is to reduce that contact time or make the extraction less aggressive. The first and most important tool to achieve this is your grinder.

The primary dial: Adjusting your grind size

Your grinder is the most critical piece of equipment for dialing in espresso. The size of your coffee grounds directly controls how fast water can flow through them. This relationship is the key to managing extraction time and, therefore, bitterness.

A finer grind creates more surface area and a more compact coffee puck. This provides more resistance, slowing down the water flow and increasing the total extraction time. If your grind is too fine, you get a long, slow shot that becomes bitter.
A coarser grind creates less surface area and more space between particles. This provides less resistance, allowing water to flow through faster and reducing the total extraction time.

Therefore, the golden rule is simple: If your espresso is bitter, your grind is likely too fine. To fix it, you must make your grind coarser. This will speed up your shot, reducing the overall contact time and preventing the water from extracting those final bitter compounds.

Follow these steps to adjust your grind:

Keep all other variables the same. Don’t change your coffee dose or the amount of espresso in your cup (your yield).
Make one small adjustment on your grinder towards a coarser setting.
Pull another shot, timing it from the moment you press the button to when you hit your target yield.
Taste it. A common target for a balanced shot is between 25-32 seconds. If your previous bitter shot took 40 seconds, and this new one takes 30, you are moving in the right direction. The bitterness should be reduced, replaced by more sweetness and balance.

Continue making small adjustments until the bitterness disappears and you have a shot that tastes rich and sweet. Once your shot time is in the ideal range, but you still taste a hint of bitterness, it’s time to look at our second variable.

The flavor refiner: Tuning the brewing temperature

Think of grind size as your coarse adjustment and brew temperature as your fine-tuning dial. Water temperature has a major impact on how efficiently flavors are extracted. Hotter water is a more aggressive solvent; it dissolves compounds much faster. If your grind size and shot time are seemingly perfect, but a harsh bitterness lingers, your brew water might simply be too hot.

A high temperature can scorch the delicate coffee grounds on contact and rapidly extract the bitter elements, even within a normal 30-second window. This is especially true for darker roasts, which are more porous and soluble after the roasting process and extract very easily.

If you suspect temperature is your issue, here’s the fix:

Lower the temperature. If your machine has a PID or temperature control, reduce it by 1-2°C (or 2-4°F).
Keep your grind setting the same. Remember to only change one variable at a time.
Pull a new shot and taste the difference. That small temperature drop can be enough to shave off the harsh edge, revealing more delicate chocolatey or nutty notes underneath.

Conversely, lighter roasts are much denser and less soluble, often requiring higher temperatures (93-96°C / 199-205°F) to properly extract their bright, fruity flavors. Using too low a temperature with a light roast can result in sour, under-extracted shots.

A systematic approach to delicious espresso

Fixing bitter espresso isn’t about random guessing; it’s about a logical, step-by-step process. Always start with your grind size to get your shot time in the right ballpark, and then use temperature to refine the flavor. Changing one variable at a time is crucial to understanding how each adjustment affects the final taste in your cup.

Here is a simple troubleshooting table to guide you:

Problem in the Cup	Likely Cause	Primary Solution
Bitter and shot is too long (>35 seconds)	Over-extraction (grind too fine)	Make your grind coarser to shorten the shot time.
Bitter but shot time is good (25-32 seconds)	Over-extraction (temperature too high)	Lower your brew temperature by 1-2°C (2-4°F).
Sour and shot is too fast (<25 seconds)	Under-extraction (grind too coarse)	Make your grind finer to lengthen the shot time.
Both Bitter and Sour	Uneven extraction (channeling)	Focus on puck prep: distribute grounds evenly and tamp level.

By following this workflow, you can methodically diagnose your espresso and make targeted adjustments. Start with a baseline recipe, focus on grind to hit your time target, and then fine-tune with temperature to perfect the taste.

Conclusion

Conquering bitter espresso is a rewarding milestone for any home barista. As we’ve seen, that harsh, unpleasant flavor is almost always a symptom of over-extraction. By understanding this core concept, you can stop fighting your machine and start working with it. The solution lies in a systematic approach, focusing on the two most impactful variables in your control. Start by adjusting your grind size to be coarser, which shortens the extraction time and is the most common fix. Once your shot time is in the ideal range, you can then fine-tune the flavor profile by making small adjustments to your brewing temperature. Remember to change only one thing at a time. With patience and these techniques, you’ll be able to consistently pull balanced, sweet, and delicious shots worthy of any café.