Espresso Troubleshooting: Fix Sour and Bitter Shots

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Your espresso tastes wrong. Either it's sour and thin, or it's bitter and harsh, or somehow both at once. This is normal. Every person making espresso at home goes through this, including the people posting perfect latte art on Reddit. The difference is they learned how to diagnose and fix these problems. You can too.

The good news: 90% of espresso problems come down to just three variables. Grind size, dose, and extraction time. Master these and you'll pull consistently good shots. The bad news: nobody can tell you exactly what settings to use because every grinder, every machine, and every coffee behaves differently. But we can teach you how to read the feedback your shots give you and adjust accordingly.

Understanding extraction: the foundation

Before diagnosing problems, you need to understand what extraction means and why it matters.

Coffee contains thousands of compounds that dissolve into water at different rates. The first compounds to extract are acids, which taste sour and bright. The middle compounds are sugars and complex flavours. The last compounds are bitter, astringent substances.

A good espresso extracts the right balance of these compounds. Too little extraction (under-extraction) leaves you with mainly acids and thin body. Too much extraction (over-extraction) pulls out the harsh bitter compounds. Perfect extraction gets the sweet spot in the middle where sourness and bitterness balance, and the coffee's character shines through.

Extraction is controlled primarily by:

Grind size - finer grinds expose more surface area, increasing extraction. Coarser grinds extract less.

Contact time - longer extraction times mean more compounds dissolve. Shot time is influenced by grind size, dose, and pressure.

Temperature - hotter water extracts faster. Most home machines are set appropriately, so this is less often the issue.

Dose - more coffee means more resistance to water flow, which can slow extraction. It also means more total coffee extracting.

When something tastes wrong, you're adjusting these variables to find better balance.

Diagnosing sour espresso

Sour shots are the most common problem beginners face. The coffee tastes sharp, acidic, maybe a bit like underripe fruit. It lacks sweetness and body. Often it's also thin and watery.

Sour almost always means under-extraction. The water passed through too quickly, dissolving the acids but not reaching the sugars and balancing compounds.

The most likely cause: grind too coarse

This is the answer 80% of the time. If your espresso runs fast (under 20 seconds for a double shot) and tastes sour, grind finer. Keep grinding finer until shots slow down and sourness transforms into sweetness.

Most beginners don't grind fine enough because they're afraid of choking the machine. Don't be. Espresso grind should feel like powdered sugar or very fine sand. The particles should clump together slightly when you pinch them. If it feels like table salt, you're too coarse.

Adjust your grinder by small increments. One or two steps at a time. Pull a shot, taste it, adjust if needed. Keep notes so you can track what's changing.

Other causes of sour shots

Low dose can contribute to sourness. If you're dosing less than 15-16g in a double basket, water flows through too easily. Try increasing to 18-20g and see if shots improve.

Stale coffee often tastes sour and flat. Beans more than 3-4 weeks from roast date lose the CO2 that helps build resistance and body. If you can't remember when you bought your coffee, it's probably too old. Fresh beans from a local roaster or online subscription make an immediate difference.

Cold machine or cold coffee can taste sour even when extraction is correct. Make sure your machine is fully heated (15-20 minutes for most single boilers) and your cup is warmed.

Diagnosing bitter espresso

Bitter shots taste harsh, astringent, maybe burnt or ashy. The finish is unpleasant and lingers on your tongue. The coffee might be dark with little crema.

Bitter almost always means over-extraction. The water spent too long in contact with the coffee, pulling out the harsh compounds that develop late in extraction.

The most likely cause: grind too fine

If your shot runs slowly (over 40 seconds for a double) and tastes bitter, grind coarser. One or two steps at a time. The goal is shots that run in 25-35 seconds with balanced flavour.

Over-dosing can also cause slow, bitter shots. If your basket is overfilled and the puck touches the shower screen, you'll get uneven extraction and excessive contact time. Check that there's about 2-3mm headspace between the tamped puck and the screen.

Other causes of bitter shots

High temperature can cause bitterness in some coffees. If your machine runs hot or you're brewing immediately after steaming milk, give it a moment to cool. On machines with PID control, try reducing temperature by 1-2 degrees.

Dark roasted coffee is inherently more bitter than light roasts. Some bitterness is normal for espresso-roast beans. But if it's harshly bitter rather than pleasantly intense, extraction is likely the problem.

Dirty equipment creates bitter, stale flavours. Coffee oils build up on group heads, baskets, and portafilters. Backflush weekly with water, monthly with cleaning tablets. Make sure your steam wand gets wiped immediately after each use.

The confusing one: sour AND bitter at the same time

If your shots taste both sour and bitter, seemingly impossible, you're probably experiencing channeling. This is when water finds easy paths through the coffee puck instead of flowing evenly.

With channeling, some parts of the coffee over-extract (creating bitterness) while other parts under-extract (creating sourness). The result is a muddy, confused shot that's unpleasant in multiple ways.

Signs of channeling

Spraying or uneven flow from a naked portafilter. Instead of a steady stream from the centre, liquid shoots from multiple spots or the sides.

Very fast start followed by normal flow. The beginning of the shot gushes out, then slows as the channel collapses.

Inconsistent shot times with identical settings. One shot takes 25 seconds, the next takes 35, despite using the same dose and grind.

Fixing channeling

Improve distribution before tamping. Make sure grounds are evenly spread in the basket before you apply pressure. Tap the sides of the portafilter, use a distribution tool, or stir with a WDT tool.

Tamp level. If your tamp is tilted, water will preferentially flow through the low side. Use a tamping mat and press straight down.

Check your dose. Underdosing leaves space for grounds to shift and create channels. Overdosing can cause uneven compaction.

Grind quality matters. Cheap grinders produce inconsistent particle sizes (high fines). Those fines can migrate and create dense spots that water avoids. A better grinder helps, but distribution technique can compensate.

The systematic approach to dialling in

Rather than randomly adjusting settings, use a systematic method to dial in new coffee.

Start with a baseline recipe

For most coffees, start with: 18g dose in, 36g out (1:2 ratio), target 25-30 seconds extraction time.

Weigh your dose precisely with a scale. Weigh your output too. Timing alone is unreliable because flow rate varies.

Pull the first shot and taste

Note the extraction time and your impression of the taste. Is it sour, bitter, balanced? Thin or full-bodied? Sweet or lacking sweetness?

Adjust grind first

If the shot ran fast (under 20 seconds) or tastes sour: grind finer.

If the shot ran slow (over 40 seconds) or tastes bitter: grind coarser.

Make small adjustments. One or two steps on your grinder. Pull another shot.

Change only one variable at a time

This is crucial. If your shot tastes sour and you simultaneously grind finer, increase dose, and add pre-infusion, you won't know which change fixed the problem (or made it worse).

Change one thing. Pull a shot. Evaluate. Repeat.

Dial in over multiple shots

Expect to spend 3-5 shots dialling in a new coffee. Your first attempt is a starting point, not a final destination. Each shot gives you information to guide the next adjustment.

Once you've found good settings, they'll work for that bag of coffee until it ages significantly (after 2-3 weeks, you may need to adjust as beans degas).

Common problems with specific causes

Shot runs in under 15 seconds, tastes extremely sour

Grind is way too coarse. Adjust significantly finer, maybe 5-10 steps on your grinder. If you can't grind fine enough to slow the shot down, your grinder may not be capable of espresso.

Shot runs in over 50 seconds, chokes the machine

Grind is too fine or dose is too high. Adjust coarser or reduce dose by 1-2g. Check that the basket isn't overfilled.

Shot looks good but tastes bland and lifeless

Probably stale coffee. Check the roast date. Beans more than 4 weeks old often taste flat and muted regardless of extraction. Buy fresher beans.

Shot gushes initially then slows dramatically

Channeling. Improve distribution before tamping. Use a WDT tool to break up clumps and distribute evenly.

Shot time is perfect but tastes bitter

Try a slightly coarser grind and faster shot. Some coffees taste better at 22-25 seconds rather than 30+. Alternatively, check machine temperature if you have adjustment capability.

Shot time is perfect but tastes sour

Try a slightly finer grind and longer shot. Some coffees, especially light roasts, need 30-35 seconds for proper extraction. You can also try a longer ratio (1:2.5 or 1:3 instead of 1:2).

Shots are wildly inconsistent despite consistent technique

Your grinder is likely the problem. Budget grinders can't produce consistent enough particle sizes for reliable espresso. If shot times swing between 20 and 40 seconds with identical technique, upgrade your grinder.

When to adjust ratio instead of grind

Sometimes grind adjustments alone can't fix the taste. That's when ratio changes help.

Longer ratios (1:2.5 or 1:3, meaning 18g in, 45-54g out) extract more from the coffee. This can help with light roasts that taste sour even at normal ratios. The extra liquid dilutes intensity but brings out more sweetness.

Shorter ratios (1:1.5 or 1:2, meaning 18g in, 27-36g out) are more concentrated and intense. This works well for darker roasts or coffees with flavours that get muddied by too much extraction.

Experiment with ratio once you've got grind dialled in reasonably well. Some coffees taste dramatically better at non-standard ratios.

Equipment that helps troubleshooting

A scale with 0.1g precision (£15-20 on Amazon) - absolutely essential. Weighing input and output removes guesswork.

A naked portafilter (£15-30) - shows exactly what's happening during extraction. You can see channeling, uneven flow, and the colour development of your shot.

A WDT tool (£5-15) - thin needles for stirring and distributing grounds. Reduces channeling significantly.

A thermometer (£10-15) - verifies your machine is reaching proper brewing temperature if you suspect temperature issues.

You don't need expensive accessories to make good espresso, but a scale is genuinely non-negotiable.

Temperature and pressure issues

Most home machines ship with appropriate temperature and pressure settings. But occasionally these cause problems.

Signs of temperature issues

Shots consistently taste thin and sour even with very fine grinds may indicate low temperature. The machine might not be heating properly or might need longer warm-up time.

Shots consistently taste burnt or overly bitter might indicate high temperature. Some older Gaggia Classics ran hot and needed OPV adjustment.

Check your machine's specifications. Most espresso machines target 90-96°C. Machines with PID control let you adjust this. Without PID, temperature is harder to manage.

Signs of pressure issues

Very fast shots that resist slowing down even with fine grinds might indicate low pressure. The machine may need servicing or the pump may be failing.

Shots that choke easily even at medium grinds might indicate overly high pressure. Some older machines shipped with OPV set to 12+ bar instead of 9 bar. This can be adjusted on many machines.

Pressure problems are less common than grind problems, so check grind first.

The role of fresh coffee

This can't be overstated: fresh coffee changes everything.

Supermarket coffee is often 3-6 months old by the time you open it. That coffee has lost most of its CO2 and volatile aromatics. It extracts differently (usually poorly), tastes flat, and won't produce the crema or body you expect from espresso.

Fresh coffee from a roaster (roasted within the last 2-3 weeks) extracts more predictably, tastes more vibrant, and produces better texture.

If you're struggling with extraction and can't find good settings, try new beans from a specialty roaster before blaming your equipment. Often fresh coffee is the main thing missing.

What "dialled in" actually means

When people say they're "dialled in," they mean they've found grind settings and technique that produce consistent, good-tasting shots with their current coffee.

Being dialled in doesn't mean perfect shots every time. Small variations in room humidity, bean age, and technique create minor differences. But shots should be consistently in a good range, all tasting enjoyable with minor variations.

Once dialled in, you shouldn't need to adjust grind much until the coffee ages noticeably (after 2-3 weeks) or you open a new bag. Dialling in a new bag takes a few shots but becomes faster with experience.

Getting help when stuck

If you've been troubleshooting for a week and can't pull drinkable shots, ask for help. Post to r/espresso or a home barista forum with:

- Your machine and grinder - Your dose, yield, and time - What the shot looks like (photo or video helps) - What it tastes like

The community diagnoses issues quickly because they've seen every possible problem. No question is too basic.

Common questions about espresso troubleshooting

My shot tastes sour - what should I do first?

Grind finer. This is the answer 80% of the time. Keep grinding finer until shots slow down to 25-30 seconds and sourness transforms into sweetness.

How fine should espresso grind be?

Like powdered sugar or very fine sand. The particles should clump together slightly when pinched. If it feels like table salt, you're too coarse.

How do I know if my coffee is too old?

Check the roast date on the bag. Beans more than 4 weeks old often taste flat and extract poorly. If there's no roast date, assume it's too old. Supermarket coffee is almost always stale.

Why does my espresso taste both sour and bitter?

This usually indicates channeling, where water flows unevenly through the puck. Some areas over-extract while others under-extract. Fix your distribution before tamping.

How many shots should it take to dial in new coffee?

Usually 3-5 shots if you're experienced, maybe 10-15 when starting out. Each shot gives you information to guide the next adjustment. It's a learning process that gets faster with practice.

Free tools to help you dial in

Try our troubleshooting tools:

- **Dial-In Help** - Select your problem, get instant fixes - **Shot Log** - Track your shots to see what's working

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