Under-Extraction vs Over-Extraction: The Visual Guide

You did everything right. You bought fresh beans, you weighed your dose perfectly, and you tamped with precision. But when you finally take that first sip of espresso, your face immediately scrunches up.

It either tastes sharp and sour enough to strip the enamel off your teeth, or it's so intensely bitter that it leaves an ashy, dry feeling on your tongue.

Welcome to the delicate balancing act of espresso extraction.

Every single troubleshooting technique in coffee—grind size, dose, yield, and temperature—exists for one sole purpose: to move your shot away from the extremes of under-extraction and over-extraction, and into the "sweet spot" of balanced extraction.

Here is everything you need to know to diagnose your espresso purely by taste and sight.

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What Actually is "Extraction"?

When highly pressurized hot water hits your coffee puck, it doesn’t dissolve everything at once. Coffee compounds extract in a very specific, predictable sequence:

1. First (The Sours): Fats, acids, and vibrant fruity/floral flavors.
2. Second (The Sweets): Sugars and complex caramel/chocolate notes.
3. Third (The Bitters): Tannins, dry plant fibers, and harsh bitter compounds.

Perfect espresso perfectly balances the initial acids with the delayed sugars, while stopping the shot right before the harsh bitter compounds take over.

When you fail to achieve this balance, you get under or over-extraction.

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1. Under-Extraction (The Sour Shot)

Under-extraction happens when the water does not extract enough from the coffee grounds. The water flows through the puck too easily, dissolving only the early acids and fats, but failing to stick around long enough to extract the sweet sugars that balance them out.

How to Identify Under-Extraction

• Taste: Sharp, sour, salty, or highly acidic. It makes your lips pucker. It lacks sweetness and feels "hollow" or thin.
• Visuals: The shot runs extremely fast (under 20 seconds). The liquid looks pale, watery, and blondes very quickly. The crema disappears almost instantly.

Common Causes & Fixes

• Grind too coarse: Water finds massive gaps and rushes through. Fix: Grind finer.
• Yield too short: You stopped the shot too early (e.g., 20g out instead of 36g out). Fix: Let the shot run longer to extract sugars.
• Water temperature too low: Cold water is terrible at dissolving sugars. Fix: Increase brew temp to 93°C (200°F).

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2. Over-Extraction (The Bitter Shot)

Over-extraction is the exact opposite. It happens when the water extracts too much from the coffee grounds. The water spends so much time in contact with the coffee that it blows right past the acids and sugars, and begins dissolving the harsh, dry, woody plant fibers.

How to Identify Over-Extraction

• Taste: Intensely bitter, ashy, or burnt. It leaves a dry, astringent feeling on your tongue (like over-steeped black tea). You cannot taste the individual origin notes of the bean.
• Visuals: The shot struggles to come out. It drips slowly (taking 40+ seconds). The liquid looks incredibly dark, almost black, and the crema may have a dark brown ring around the edge.

Common Causes & Fixes

• Grind too fine: Water cannot physically push through the puck, resulting in a painfully slow drip. Fix: Grind coarser.
• Yield too long: You let the shot run way past your target ratio. Fix: Stop the shot earlier.
• Channeling: Water found a weak spot and relentlessly extracted from that one tiny channel, heavily over-extracting a small percentage of coffee. Fix: Distribute and tamp evenly (WDT).

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The "Salami" Shot Experiment

If you still struggle to differentiate between sour (under) and bitter (over), try the Salami Shot experiment:

1. Prepare your normal espresso shot.
2. Line up 4 small espresso cups.
3. Start the shot. Every 7 seconds, swap to the next cup.
4. Taste them in order.

• Cup 1 (0-7s): Intensely sour, thick, salty.
• Cup 2 (7-14s): Sweet, acidic, balanced.
• Cup 3 (14-21s): Watery, mild, starting to get bitter.
• Cup 4 (21-28s+): Pure ashy, dry bitterness.

Understanding this flow of extraction is the absolute key to dialing in espresso. If your coffee is too sour, you need to extract more. If it is too bitter, you need to extract less.

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