Espresso: The Art of Extraction
- The Caffeinatrix
- Nov 11
- 5 min read
“Espresso” comes from the Italian word esprimere, meaning “to press out”. This is quite fitting because this coffee style is all about expressing the bean’s essence under pressure. Born in early 20th-century Italy, espresso remains a cornerstone of specialty coffee culture and a precision craft in its own right.
Pulling a beautiful shot isn’t about luck, it’s about science, craft and precision. If you’ve ever tasted a sour, weak shot or a brittle, bitter one and wondered what went wrong, this post is for you. We’ll focus on how to aim for the “sweet zone” of extraction, what variables you control, what happens when things go wrong, and how you can calibrate your workflow for consistently excellent espresso.
Proper Extraction Defined
Extraction in espresso is the process of dissolving soluble coffee compounds into water under pressure. The objective is to extract the desirable compounds such as acids, sugars, and oils, while avoiding undesirable compounds like excessive tannins and burnt/smoky bitterness. The Specialty Coffee Association (SCA) emphasizes the importance of extraction yield. This refers to the percentage of coffee grounds dissolved as a key quality metric (SCA Brewing Research).
The SCA’s barista survey in 25 Magazine notes that many baristas use around an 18-20 g dose, aim for ~36 g out, in ~25-30 seconds at ~9 bars of pressure (SCA 25 Magazine Issue 3). While extraction yield targets vary by equipment and roast, the “sweet zone” for espresso often sits near 18-22% yield (SCA). When extraction is too low or too high, this is when you run into problems.
Under-Extracted vs Over-Extracted
Under-extracted
When a shot is under-extracted (too low yield/time/resistance), you’ll likely notice:
Sharp sourness or green acidity. This is because early-dissolving acids will dominate
Thin body, weak sweetness, lack of richness
Possibly grassy, vegetal or hollow flavor
Common causes: too coarse a grind which results in an insufficient surface area, too fast flow (low resistance), too little dose, insufficient tamp/distribution or inadequate water pressure/time.
Over-extracted
When extraction goes too far or continues too long, the result can be:
Bitter, dry-mouth, astringent finish. This is sometimes a burnt or hollow roast flavor
Loss of nuance occurs when the origin or roast character is masked by undesireable flavors or aromas often referred to as "off-notes"
Flat or overly heavy mouthfeel. This is where taste complexity disappears
Common Causes: too fine a grind which results in an excessive surface area, long flow time or mass out, excessive dose/resistance, channeling, or machine/pressure irregularities. The brewing control charts show that when yield rises past the ideal zone, unwanted compounds will dominate (SCA towards-a-new-brewing-chart).
The “sweet zone”
For a typical specialty espresso setup, aiming for ~25-30 seconds extraction, around 9 bars of pressure, a 1:2 brew ratio (for example, 18 g in → ~36 g out) is a solid starting point (SCA 25 Magazine Issue 3). From there, you can make adjustments according to your taste preference.
Grind size: The most influential variable
Grind size is probably your most powerful tool since it directly impacts surface area and extraction rate:
finer = more surface area = faster extraction/resistance.
coarser = less surface area = slower extraction.
Research shows grind size, along with pressure and temperature, significantly affects extraction yield and total dissolved solids (TDS) in espresso systems (Winarso et al., 2024).
In practice:
If your shot pours too quickly (<20 s, thin stream): your grind may be too coarse and will likely be under-extracted.
If your shot pours too slowly or is barely flowing (>35 s, dense stream): your grind may be too fine or the resistance is too high. This can lead to over-extraction or channeling.
The “ideal” grind size depends on your machine, doser, basket size, puck depth, water path, and even environmental factors like humidity. Calibration is key.
Pressure, calibration, tamping & channeling
Pressure & calibration
Espresso machines are typically configured to operate near 9 bars of pressure. This is a standard reference mentioned by the SCA. (SCA 25 Magazine Issue 3). When machine pressure, group head seals, or flow circuits are misaligned or worn out, the extraction process becomes inconsistent, causing uneven flow, unpredictable resistance, and varying results. Regular machine maintenance is crucial. This includes back-flush, group head gasket checks, and portafilter inspections.
Tamping & distribution (avoiding channeling)
Tamping is not about brute force—it’s about achieving even density and consistent puck structure. If your grounds are uneven or loosely compacted, water will exploit weak paths (channeling) and bypass coffee, causing uneven extraction zones (some over-extracted, some under). Studies on microstructure confirm that non-uniform extraction degrades quality (ArXiv Coffee Extraction Dynamics, 2022).
Best practice:
Distribute grounds level in the basket before tamping.
Use a firm, level tamp (~30 lbs force is common guideline).
Purge the group head, lock in portafilter, start extraction.
Inspect for visible flow issues (gushers, visible cracks, erratic streams) as signs of channeling. If present, revise distribution/tamp or adjust grind.
Putting it all together: A workflow
Pre-heat machine, portafilter, group head.
Dose your grounds (e.g., 18 g).
Grind to your initial setting (based on previous benchmark).
Distribute grounds level, tamp firmly and evenly, purge group head.
Lock portafilter and begin extraction. Observe flow: aim for stable honey-like stream.
Aim for output and time (e.g., ~36 g out in ~25-30 s). If your shot is too fast: grind finer. Too slow: grind coarser.
Taste the shot: if it is sour or weak, it is likely under-extracted. If it is bitter, dry or astringent, it is likely over-extracted. Adjust accordingly.
Maintain machine health: monitor the pressure gauge, clean the group head, inspect seals, and back-flush regularly.
Why it matters
As a premium coffee brand, the difference between an “okay shot” and “exceptional shot” defines your customer experience. A properly extracted espresso reveals the complexity of your roasted beans. Showcase a bright, citrusy single origin or a chocolatey medium roast designed for milk-based drinks. Poor extraction can mask or disrupt the true complexity of flavors. Teaching customers and baristas the basics of proper extraction will not only boost your brand’s value but also enhance the customer experience.
Extraction is where science, craft and tasting merge. Grind size, time, pressure, tamping—they’re your dials. Calibrate them. Maintain your machine. Listen with your palate. When you find that perfect balance, you’ll brew espresso that’s not only strong, but also rich, complex, and true to the essence of the coffee.
Selected References
Specialty Coffee Association. The Coffee Taster’s Flavor Wheel. SCA/WCR Sensory Lexicon and Wheel. https://sca.coffee/research/coffee-tasters-flavor-wheel
Williams, S. D. (2022). Does Coffee Have Terroir and How Should It Be Assessed? Frontiers / PMC. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9265435/
Seninde, D. R. (2020). Coffee Flavor: A Review. Beverages (MDPI). https://www.mdpi.com/2306-5710/6/3/44
Angeloni, S., et al. (2021). Characterization of the Aroma Profile and Main Key Odorants in Coffee. Foods. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8270317/
ArXiv Coffee Extraction Dynamics. (2022). Modeling Espresso Channeling and Flow Distribution in Coffee Pucks. arXiv preprint [physics/2205.09423]. https://arxiv.org/abs/2205.09423
Córdoba, N., et al. (2020). Coffee Extraction: A Review of Parameters and Their Role in Cup Quality. Trends in Food Science & Technology.
Lapčíková, B., et al. (2023). Effect of Extraction Methods on Aroma Profile and Antioxidant Activity of Filtered Coffee. Foods
Smrke, S., et al. (2024). The Role of Fines in Espresso Extraction Dynamics. Scientific Reports / Nature. https://www.nature.com/articles/s41598-024-55831-x
Genovese, A. (2025). The Impact of Brewing Methods on the Quality of a Cup of Coffee. Beverages (MDPI). https://www.mdpi.com/2306-5710/11/5/125
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