7 Common Espresso Mistakes (And How to Fix Them)

Most bad home espresso traces back to a handful of fixable variables: grind size, dose, tamp, water temperature, and bean freshness. Use the espresso diagnosis tool to match your symptoms (sour, bitter, watery, weak crema) to the specific fix below.

Mistake #1: Wrong Grind Size

Grind size is the most common cause of bad espresso. If the grind is too coarse, water rushes through the puck in under 20 seconds, producing a pale, thin, sour shot from under-extraction. If the grind is too fine, water can barely push through; the shot takes 40+ seconds and comes out dark, bitter, and astringent from over-extraction.

Target: 25-30 seconds to pull 36g of liquid espresso from an 18g dose (a 1:2 ratio). If the shot finishes under 20 seconds, grind finer. If it runs past 35 seconds or barely drips, grind coarser. Adjust in small steps, 1-2 clicks on the grinder at a time, and pull a new shot after each change. See the full grind size guide for reference settings by brew method.

Mistake #2: Inconsistent or Bad Tamping

Uneven tamping (pressing harder on one side than the other) creates channels that water follows preferentially, over-extracting that section while under-extracting the rest. The result is a shot that reads as both bitter and sour at once, a classic channeling symptom: instead of a steady, even stream from the portafilter spouts, you'll see a fast, thin spritz or an off-center jet.

Tamp pressure matters less than levelness. Place the portafilter on a flat surface or tamping mat, hold the tamper vertically, and press straight down until the coffee stops compressing (roughly 15-20 lbs of even pressure, though the exact number matters far less than consistency). Keep the wrist straight and the elbow directly above the portafilter so the tamp lands flat. A calibrated tamper that clicks at a set pressure can help beginners build consistency, but a level, even press solves most tamping-related channeling on its own.

Mistake #3: Using the Wrong Dose

Eyeballing the dose introduces a variable that swings extraction dramatically: even ±1g changes puck density enough to shift extraction time by several seconds. Too much coffee packs the puck too dense, slowing flow and pushing toward over-extraction and bitterness. Too little leaves headspace above the puck, water hits it unevenly, and channeling produces a sour, thin shot.

Use a scale that reads to 0.1g (roughly $15-25 for a basic model) and weigh the dose every time. For most double baskets, the working range is 17-19g, with 18g the most common starting point; check the rating stamped on the basket or listed by the manufacturer and stay within a gram of that figure. Log doses and shot times with the espresso shot journal to spot drift before it shows up as a bad cup.

Mistake #4: Using Stale Beans

Espresso is unforgiving with stale beans. As beans age, the CO2 that drives crema production dissipates and volatile aromatics fade, flattening flavor. Beans are at their best roughly 7-30 days post-roast: the first week they're still degassing heavily, which can make shots inconsistent, and past about 30 days flavor declines noticeably.

Buy from a roaster that prints a roast date (not a "best by" date), buy only a 2-3 week supply, and store beans in an airtight container away from light, heat, and moisture.

Mistake #5: Wrong Water Temperature

Most espresso machines extract best between 90-96°C (195-205°F). Too hot pulls harsh, bitter, ashy flavors from over-extraction. Too cold produces a sour, thin shot from under-extraction.

If the machine has a PID controller, set it in the 93-94°C (200-201°F) range as a starting point. For lighter roasts, 95-96°C helps extract denser beans; for darker roasts, dropping to 90-92°C avoids burnt, smoky notes. Without a PID, temperature-surf: flush water through the group, let the boiler stabilize for 20-30 seconds, then pull the shot.

Mistake #6: Not Preheating Your Equipment

A cold portafilter, group head, and cup pull heat out of the water during extraction, dropping the effective brew temperature by several degrees, which shows up as under-extraction, sourness, and thin body.

Turn the machine on 15-20 minutes before brewing. Lock the empty portafilter into the group head while it heats so both reach temperature together. Run a blank shot (water only, no coffee) right before dosing, and preheat the cup with hot water or on the machine's cup warmer. These steps add under two minutes total but keep the first shot of the day consistent with every shot after it.

Mistake #7: Not Cleaning Your Machine

Coffee oils deposit on the group head, shower screen, and portafilter basket with every shot. Given time, those oils turn rancid and taste stale, acrid, and bitter, an off-flavor that no amount of grind or dose adjustment will dial out.

Flush the group head with water and wipe the portafilter basket after every session. Backflush weekly with a cleaning powder (like Cafiza) if the machine has a three-way solenoid valve. Soak the basket and shower screen in cleaning solution for 15-20 minutes monthly. Descale the boiler every 2-3 months per the manufacturer's instructions.

Bringing It All Together

Grind size and dose consistency, fresh beans, and a clean machine resolve the majority of espresso problems. Water temperature, tamping, and preheating are the refinements that take a shot from good to great once those fundamentals are locked in. Run the espresso diagnosis tool against your specific symptoms, and track changes in the shot journal to see which fix actually moved the needle.