{ "id": "espresso-recipes-and-ratios", "url": "https://coffearium.org/entries/espresso-recipes-and-ratios/", "license": "CC-BY-4.0", "title": "Espresso recipes and ratios", "summary": "How an espresso recipe is written – dose, beverage mass, ratio, time, temperature and pressure – what each setting does to strength, extraction and flavour, and how baristas calculate and adjust a shot.", "domain": "extraction", "kind": "Method", "stage": "brew", "topics": [ "science" ], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-19T00:00:00.000Z", "updated": "2026-10-19T00:00:00.000Z", "added": "2026-10-19T00:00:00.000Z", "brief": [ "An espresso recipe names the dose of dry coffee, the beverage mass in the cup and the ratio between them; time, temperature and pressure complete it.4,3", "The Certified Italian Espresso uses 7 ± 0.5 g of coffee for a 25 ± 2.5 mL cup in 25 ± 2.5 s, at 9 ± 1 bar, as reported in a 2013 study.3", "In a 2023 study with a 20 g dose, ristretto, espresso and lungo were defined as about 1:1, 1:2 and 1:3, dose to beverage.4", "In the same study, the beverage mass collected changed the cup far more than flow rate, grind or temperature did.4", "Extraction yield = TDS × beverage mass ÷ dose. A typical espresso dissolves about 20% of the coffee, according to a 2024 study.5" ], "quickFacts": [ { "label": "Recipe written as", "value": "Dose (g) → beverage (g), e.g. 20 g → 40 g = 1:2" }, { "label": "Certified Italian Espresso", "value": "7 ± 0.5 g; 25 ± 2.5 mL with foam; 25 ± 2.5 s; 9 ± 1 bar; 90 ± 2 °C (as reported)" }, { "label": "Ristretto · espresso · lungo", "value": "≈1:1 · ≈1:2 · ≈1:3 (one 2023 study, 20 g dose)" }, { "label": "Doses in research recipes", "value": "16 g; 18 g; 20 g" }, { "label": "Typical extraction yield", "value": "About 20%" }, { "label": "Flow into the cup", "value": "Ideally close to 1 mL/s; 0.40–2.73 mL/s in Italian cafés (survey)" }, { "label": "Core equation", "value": "EY = TDS × beverage mass ÷ dose" } ], "aka": [ "Espresso recipe", "Espresso brew ratio", "Espresso ratio", "Dialling in" ], "linkTerms": [ "espresso recipe", "espresso recipes", "espresso ratio", "ristretto", "lungo", "dialling in", "dialing in", "dial in" ], "related": [ "espresso", "espresso-machine", "puck-preparation", "extraction-yield-and-tds", "grinding", "particle-size-and-fines", "grinder-types-and-burrs", "water-for-coffee", "brew-methods", "caffeine" ], "contested": [ "Certified Italian Espresso parameters: a 2013 study gives brew water at 90 ± 2 °C, 25 ± 2.5 s and 25 ± 2.5 mL in the cup3, while a 2017 textbook chapter gives 88 ± 2 °C, 25 ± 5 s and 25–40 mL.1 Both give 7 ± 0.5 g and 9 ± 1 bar. The institute’s own document was not opened for this entry.", "Effect of brew temperature: in an on-line aroma study, raising the water from 82 to 96 °C increased the extraction of volatile compounds7; in a flow-controlled study, changing the temperature on its own from 80 to 98 °C had no measurable influence on trigonelline, caffeine, 5-CQA or TDS in the cup.4 The same 2023 study describes earlier temperature studies as inconclusive.4", "Effect of pump pressure: in one study, shots at 7 and 9 bar did not differ in aroma, while 11 bar extracted more volatiles7; a 2023 study summarises earlier work in which raising pressure from 7 to 11 bar tended to lower the mass of compounds in the cup.4 Volatile aroma and non-volatile compounds were measured, so the findings need not conflict.", "What “lungo” means: a 2023 study defines espresso lungo as about 1:3, dose to beverage4; a 2013 comparison describes a lungo as a larger cup of 100–250 mL and made its machine lunghi at 2 × 120 mL from 16 g.6" ], "corrections": [ { "date": "2026-10-19T00:00:00.000Z", "change": "Removed values that rested on one textbook only (water-to-coffee 3.5–6 mL/g, 25–30 s, 8–19 bar, the 18% and 22% yield limits, 16 g for two 16 g cups).", "reason": "Number rule – one Tier A or two independent Tier B sources required; the Folmer chapters count as one source." }, { "date": "2026-10-19T00:00:00.000Z", "change": "The ratio of beverage mass to dose is now called the beverage ratio, as in the extraction yield entry; the study's term “brew ratio” is mentioned once.", "reason": "On this site brew ratio means water ÷ coffee; the old wording clashed with the extraction yield entry." }, { "date": "2026-10-19T00:00:00.000Z", "change": "Ristretto, espresso and lungo in the 2023 study are described as defined and calculated, not brewed; the 2007 study's ratios as pointed to by sensory attributes, not chosen.", "reason": "Matches what the study and the abstract state." } ], "sources": [ { "id": "s1", "title": "The Brew – Extracting for Excellence", "authors": "Mestdagh, F.; Glabasnia, A.; Giuliano, P.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 15, pp. 355–380", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00015-3", "doi": "10.1016/B978-0-12-803520-7.00015-3", "tier": "B", "quote": "Small adjustments and frequent tasting are therefore best practices, as well as objective measurement when possible.", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s2", "title": "The Grind – Particles and Particularities", "authors": "von Blittersdorff, M.; Klatt, C.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 13, pp. 311–328", "url": "https://eld.bl.uk/catalog/018161895", "doi": "10.1016/B978-0-12-803520-7.00013-X", "tier": "B", "quote": "This increases dosing accuracy and helps locking the coffee-to-beverage ratio in the preparation process.", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s3", "title": "Importance of Espresso Coffee Machine Parameters on the Extraction of Chlorogenic Acids in a Certified Italian Espresso by Using SPE-HPLC-DAD", "authors": "Caprioli, G.; Cortese, M.; Odello, L.; Ricciutelli, M.; Sagratini, G.; Tomassoni, G.; Torregiani, E.; Vittori, S.", "year": 2013, "publisher": "Journal of Food Research 2(3), 55–64", "url": "https://www.openaccessrepository.it/record/70454/files/fulltext.pdf", "doi": "10.5539/jfr.v2n3p55", "tier": "A", "quote": "the obtained EC had a volume of 25 ml in 25 seconds", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s4", "title": "Influence of Flow Rate, Particle Size, and Temperature on Espresso Extraction Kinetics", "authors": "Schmieder, B. K. L.; Pannusch, V. B.; Vannieuwenhuyse, L.; Briesen, H.; Minceva, M.", "year": 2023, "publisher": "Foods 12(15), 2871", "url": "https://mdpi-res.com/d_attachment/foods/foods-12-02871/article_deploy/foods-12-02871.pdf", "doi": "10.3390/foods12152871", "tier": "A", "quote": "The ratio between the ground coffee mass in the puck and the extracted EC mass in the cup is called the brew ratio (BR).", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s5", "title": "The role of fines in espresso extraction dynamics", "authors": "Smrke, S.; Eiermann, A.; Yeretzian, C.", "year": 2024, "publisher": "Scientific Reports 14, 5612", "url": "https://www.nature.com/articles/s41598-024-55831-x", "doi": "10.1038/s41598-024-55831-x", "tier": "A", "quote": "During a typical espresso extraction around 20% of the solid coffee material is solubilized and extracted into the beverage (extraction yield).", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s6", "title": "Comparison of nine common coffee extraction methods: instrumental and sensory analysis", "authors": "Gloess, A. N.; Schönbächler, B.; Klopprogge, B.; D’Ambrosio, L.; Chatelain, K.; Bongartz, A.; Strittmatter, A.; Rast, M.; Yeretzian, C.", "year": 2013, "publisher": "European Food Research and Technology 236, 607–627", "url": "https://digitalcollection.zhaw.ch/bitstream/11475/4251/2/2013_Gloess-etal_Comparison-of-nine-common-coffee-extraction-methods.pdf", "doi": "10.1007/s00217-013-1917-x", "tier": "A", "quote": "Espresso is a concentrated beverage of 20 ml to 40 ml, brewed by forcing hot water at high pressure (up to 19 bars) through finely ground coffee and made for immediate consumption.", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s7", "title": "Extraction kinetics of coffee aroma compounds using a semi-automatic machine: On-line analysis by PTR-ToF-MS", "authors": "Sánchez López, J. A.; Wellinger, M.; Gloess, A. N.; Zimmermann, R.; Yeretzian, C.", "year": 2016, "publisher": "International Journal of Mass Spectrometry 401, 22–30", "url": "https://doi.org/10.1016/j.ijms.2016.02.015", "doi": "10.1016/j.ijms.2016.02.015", "tier": "A", "quote": "A pressure of 11 bar resulted in an increased extraction of volatiles over the entire extraction time (25 s).", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s8", "title": "Neglected Food Bubbles: The Espresso Coffee Foam", "authors": "Illy, E.; Navarini, L.", "year": 2011, "publisher": "Food Biophysics 6(3), 335–348", "url": "https://link.springer.com/article/10.1007/s11483-011-9220-5", "doi": "10.1007/s11483-011-9220-5", "tier": "A", "quote": "An “over extracted” espresso exhibits either a white foam with large bubbles if the water was too hot or just a white spot in the center of the cup if brewing time was too long.", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s9", "title": "Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment", "authors": "Cameron, M. I.; Morisco, D.; Hofstetter, D.; Uman, E.; Wilkinson, J.; Kennedy, Z. C.; Fontenot, S. A.; Lee, W. T.; Hendon, C. H.; Foster, J. M.", "year": 2020, "publisher": "Matter 2(3), 631–648", "url": "https://pure.hud.ac.uk/en/publications/systematically-improving-espresso-insights-from-mathematical-mode/", "doi": "10.1016/j.matt.2019.12.019", "tier": "A", "quote": "experimental measurements show a peak in the extraction yield versus grind setting relationship.", "abstractOnly": true, "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s10", "title": "Optimization of espresso coffee extraction through variation of particle sizes, perforated disk height and filter basket aimed at lowering the amount of ground coffee used", "authors": "Khamitova, G.; Angeloni, S.; Borsetta, G.; Xiao, J.; Maggi, F.; Sagratini, G.; Vittori, S.; Caprioli, G.", "year": 2020, "publisher": "Food Chemistry 314, 126220", "url": "https://pubblicazioni.unicam.it/handle/11581/432070", "doi": "10.1016/j.foodchem.2020.126220", "tier": "A", "quote": "Extracting with smaller particles escalates the quantity of bioactive compounds.", "abstractOnly": true, "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s11", "title": "Influence of coffee/water ratio on the final quality of espresso coffee", "authors": "Andueza, S.; Vila, M. A.; de Peña, M. P.; Cid, C.", "year": 2007, "publisher": "Journal of the Science of Food and Agriculture 87(4), 586–592", "url": "https://dadun.unav.edu/handle/10171/35076", "doi": "10.1002/jsfa.2720", "tier": "A", "quote": "6.5 g 40 mL(-1) or 7.5 g 40 mL(-1) in conventional roasted coffees", "abstractOnly": true, "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s12", "title": "Brew temperature, at fixed brew strength and extraction, has little impact on the sensory profile of drip brew coffee", "authors": "Batali, M. E.; Ristenpart, W. D.; Guinard, J.-X.", "year": 2020, "publisher": "Scientific Reports 10, 16450", "url": "https://www.nature.com/articles/s41598-020-73341-4", "doi": "10.1038/s41598-020-73341-4", "tier": "A", "quote": "In this study, we drip-brewed coffee to specific brew strengths, as measured by total dissolved solids (TDS), and extraction yields, as measured by percent extraction (PE), spanning the range of the classic Coffee Brewing Control Chart.", "abstractOnly": true, "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s13", "title": "Coffee Decoded: The Science of “Dialing-In”", "authors": "Giuliano, P.", "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/sca-news/coffee-decoded-14-dialling-in", "tier": "B", "quote": "It’s a kind of tuning: adjusting variables methodically until the optimal flavor appears.", "accessed": "2026-10-19T00:00:00.000Z" }, { "id": "s14", "title": "Water for Extraction – Composition, Recommendations, and Treatment", "authors": "Wellinger, M.; Smrke, S.; Yeretzian, C.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 16, pp. 381–398", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00016-5", "doi": "10.1016/B978-0-12-803520-7.00016-5", "tier": "B", "quote": "An extreme example is an espresso, which can be prepared with a dry coffee mass to beverage mass ratio of 1:2 (16 g of coffee to make to two cups, each containing a beverage of 16 g or less).", "accessed": "2026-10-19T00:00:00.000Z" } ], "markdown": "## What an espresso recipe contains\n\nAn espresso recipe is a short list of settings. Two of them define it. The **dose** is the mass of dry ground coffee in the basket.4 The **beverage mass** is the weight of espresso in the cup.4 In café use the beverage mass is also called the yield. This entry avoids that word, because “extraction yield” means something else (see below).\n\nThe **beverage ratio** links the two: beverage mass ÷ dose, written as dose to beverage.4 A 20 g dose that gives 40 g of espresso is therefore 1:2.4,5 A 2023 study calls this ratio the “brew ratio”.4 On this site, brew ratio means water ÷ coffee, the usual way to describe filter coffee (see the extraction yield entry). A coffee science textbook also describes espresso by the ratio of dry coffee to beverage mass.14\n\nThe other settings complete the recipe:\n\n- **Time.** Shot time. In one aroma study it was counted from the start of the pump.7\n- **Water temperature** at the group.3\n- **Pump pressure**, or the flow rate on machines that control flow.3,4\n- **Pre-infusion**, a first phase that fills the basket and wets the bed. In one flow-controlled study it ran at 7 mL/s until the pressure rose above 2.5 bar.4\n- **Grind.** The grinder setting that makes the bed slow the water enough.1\n- **Basket.** It holds the dose. According to a textbook, too much coffee leaves the bed no room to swell.1 How the coffee is spread and tamped in it is covered in the puck preparation entry.\n\nSome definitions give the cup in millilitres. The Certified Italian Espresso, for example, is defined by volume, with the foam included.3 According to a grinding chapter of a coffee science textbook, espresso machines with scales stop the shot at a set beverage weight.2 Grinders that dose by weight then lock the coffee-to-beverage ratio.2\n\n## Named formats\n\n**Certified Italian Espresso.** The Italian Espresso National Institute (Istituto Nazionale Espresso Italiano, INEI) specifies a single espresso by a set of values. As reported in a 2013 study, they are 7 ± 0.5 g of coffee and water leaving the machine at 90 ± 2 °C.3 The pressure is 9 ± 1 bar, the time 25 ± 2.5 s and the cup 25 ± 2.5 mL, including foam.3 A textbook chapter reports 88 ± 2 °C, 25 ± 5 s and a 25–40 mL cup for the same definition (see Contested).1 The 2013 authors note that meeting these values is not enough on its own for quality.3\n\n**Ristretto, espresso and lungo.** These names describe how much beverage is taken from the same dose. In a 2023 study, ristretto, espresso and espresso lungo were about 1:1, 1:2 and 1:3, from a 20 g dose.4 That means 20 g, 40 g and 60 g in the cup.4 A 2013 comparison used “lungo” more broadly, for a less intense coffee in a larger cup of 100–250 mL.6 Its machine lunghi were 120 mL per cup.6 No standard opened for this entry defines ristretto or lungo.\n\n**Single and double.** The Italian definition uses about 7 g for one cup.3 Research recipes use larger doses of 16 g, 18 g or 20 g.4,5,6,7 In two of these studies, “double” named the basket or the shot, not always two cups.6,7 In one study, 16 g gave two espressos of 30 mL.6 In another, 18 g in a double basket gave one shot of about 30 g.7\n\n**Cup size in Italy.** According to a 2011 review, the shot runs until the cup meets the drinker’s preference or the regional tradition.8 In Italy that is 15–50 mL, with 25–30 mL as the optimal outcome for a regular espresso.8\n\n
\n
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Beverage per gram of coffee in espresso recipes from the sources of this entry.3,4,5,6,7 Ratios are our own arithmetic from the doses and cups reported. The two recipes given in millilitres include the foam and are not directly comparable with weighed shots.
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\n\n## What each setting changes\n\n**Beverage mass and ratio.** Taking more beverage from the same dose dilutes the cup but extracts more. In a 2023 study, the beverage mass collected changed the amount of each compound in the cup more than flow rate, grind or temperature.4 In a 2013 comparison, lungo shots extracted more efficiently than espressos, because more water washed through the coffee.6 Per cup, the lunghi generally held as much of the measured compounds as the espressos, or more.6\n\n**Dose.** In a 2007 sensory and chemical study, bitterness, astringency and several flavour attributes pointed to 6.5 g or 7.5 g of coffee per 40 mL for conventionally roasted coffees.11 A 2023 study summarises earlier work: more coffee for a similar cup volume put more caffeine, trigonelline and 5-CQA in the cup.4 A textbook warns that too much coffee leaves no room to swell during wetting. In its account, the bed then compacts too much, percolation is disturbed and solids end up in the cup.1\n\n**Grind.** According to a coffee science textbook, grind is one of the main settings that decide how easily water passes through the bed.1 It is a key setting for the barista to adjust.1 A finer grind usually extracts more efficiently and also lengthens the flow time, so the two effects multiply.1 Too fine a grind can block even flow (see Deep dive).1,9\n\n**Time.** Shot time is mostly a result, not a setting. A textbook describes brewing time as the time needed to produce a given beverage volume, set by the pump and the bed together.1 In a 2024 study, shots of under 10 s and of 15 s already reached 17–18% extraction yield.5 For the one coffee tested, one panellist judged the flavour best at about 30 s and 19–20%.5\n\n**Temperature.** According to a textbook, less polar compounds, among them most bitter ones, need higher temperatures to dissolve.1 In its account, too hot water gives bitter and astringent notes, and too cool water a sweet–acidic, under-extracted cup.1 Measured effects in espresso differ between studies (see Contested).4,7\n\n**Pressure and flow.** About 9 bar is the conventional pump pressure.3 According to a textbook, the pressure on the bed is not set directly.1 It results from the push of the pump and the resistance of the bed.1 A 2011 review states that the flow into the cup should ideally be close to 1 mL/s.8 A survey cited in the review found 0.40–2.73 mL/s in Italian cafés.8 The espresso machine entry explains how pumps and the bed set pressure and flow.\n\n## Calculating ratio and extraction yield\n\nThree numbers describe a shot: dose, beverage mass and strength (TDS, total dissolved solids, read with a refractometer). From them come the ratio and the extraction yield, the share of the dry coffee that dissolved into the cup.5\n\n**Beverage ratio = beverage mass ÷ dose**, written as 1 : (beverage ÷ dose).4\n\n**Extraction yield (%) = TDS (%) × beverage mass (g) ÷ dose (g)**5\n\nA worked example, with our own arithmetic:\n\n1. Weigh the dry dose: 20.0 g.\n2. Weigh the espresso in the cup: 40.0 g. The ratio is 40.0 ÷ 20.0 = 2, written 1:2.\n3. Read the TDS of a filtered sample with a refractometer, as research labs do.5 Say it reads 9.7%, close to the 9.68% average a 2023 study reported at 1:2.4\n4. Calculate the extraction yield: 9.7% × 40.0 ÷ 20.0 = 19.4%.\n\nThe same coffee taken to 1:3 gives a weaker cup with a higher yield; at 1:1 the reverse. The figure shows this for the 2023 study.4 Because the cup is small, a few grams of beverage move the yield. In the example, 2 g more at the same TDS adds about one percentage point (our own arithmetic). The extraction yield entry explains TDS, refractometers and the brewing control chart. Its control-chart tool includes an espresso calculator.\n\n
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One coffee, one 20 g dose, three ratios: strength (TDS) falls and extraction yield rises as more beverage is taken. Our own arithmetic from the dissolved solids in the cup reported at the study’s centre point (1.9 mL/s, 88.3 °C, six replicates).4
\n
\n\n## Dialling in\n\n“Dialling in” is the routine of adjusting a recipe for a new coffee. According to the Specialty Coffee Association (SCA), baristas adjust dose, grind and extraction level methodically until the best flavour appears.13 A coffee science textbook names small adjustments, frequent tasting and objective measurement where possible as best practice.1 The steps below follow from these sources; the sequence is ours.\n\n1. **Fix the dose** by weight, leaving the bed room to swell.1,2\n2. **Fix the ratio** by stopping the shot at a set beverage weight.2\n3. **Change the grind** to change the flow and the time. Finer usually slows the shot and raises extraction; coarser does the reverse.1\n4. **Taste** after each small change.1\n5. **Measure** TDS where you can, and calculate the extraction yield.1,5\n6. **Re-check during the day.** According to the textbook, temperature and humidity in a café affect extraction.1 The barista may have to adjust over a serving day.1\n\nBaristas also use rules of thumb for target times and ratios. No study opened for this entry tested such rules, so none are given here.\n\n\n\n## Reference values\n\n| Parameter | Value reported | Context | Source |\n|---|---|---|---|\n| Dose, single | 7 ± 0.5 g | Certified Italian Espresso | Caprioli et al.3, Mestdagh et al.1 |\n| Dose, research doubles | 16.01 ± 0.01 g; 18 g; 20 ± 0.01 g | Nine-method comparison; aroma study; flow study | Gloess et al.6, Sánchez López et al.7, Schmieder et al.4 |\n| Dose per volume chosen in a sensory study | 6.5 or 7.5 g per 40 mL | Conventionally roasted coffees | Andueza et al.11 |\n| Dose reduction | 12 g vs 14 g: bioactive compounds ≈9% lower | Same cup volume, perforated disc heights varied | Khamitova et al.10 |\n| Cup, single | 25 ± 2.5 mL incl. foam; 25–40 mL | Certified Italian Espresso (two reports) | Caprioli et al.3, Mestdagh et al.1 |\n| Cup, Italian practice | 15–50 mL; 25–30 mL optimal | Regular espresso, Italy | Illy & Navarini8 |\n| Espresso and lungo by volume | 20–40 mL; 100–250 mL | Definitions in a 2013 comparison | Gloess et al.6 |\n| Ratio, ristretto · espresso · lungo | ≈1:1 · ≈1:2 · ≈1:3 (20 · 40 · 60 g from 20 g) | One study, flow-controlled machine | Schmieder et al.4 |\n| Ratio, research espresso | 1:2 (20 g → 40 g); 18 g → 31.5 ± 2 g | Fines study; aroma study | Smrke et al.5, Sánchez López et al.7 |\n| Shot time | 25 ± 2.5 s; 25 ± 5 s | Italian definition (two reports) | Caprioli et al.3, Mestdagh et al.1 |\n| Shot time, research | 28.7 ± 0.2 s (2 × 30 mL); 37.2 ± 0.3 s (2 × 120 mL) | 16 g, 92 °C, 9 bar, semi-automatic machine | Gloess et al.6 |\n| Water temperature | 90 ± 2 °C; 88 ± 2 °C | Italian definition (two reports) | Caprioli et al.3, Mestdagh et al.1 |\n| Water temperature | 92–94 °C | Review of traditional espresso | Illy & Navarini8 |\n| Pump pressure | 9 ± 1 bar; 9 ± 2 bar | Italian definition; review | Caprioli et al.3, Illy & Navarini8 |\n| Flow into the cup | Ideally close to 1 mL/s; 0.40–2.73 mL/s observed | Review; survey of Italian cafés | Illy & Navarini8 |\n| Flow-controlled shots | 1.0, 2.0, 3.0 mL/s set; 2.6–8.4 bar measured | Pre-infusion at 7 mL/s until > 2.5 bar | Schmieder et al.4 |\n| TDS at 1:2 | 9.68% (mean of all runs) | 20 g → 40 g | Schmieder et al.4 |\n| Dissolved solids in the cup | 2.92 g (1:1); 3.88 g (1:2); 4.19 g (1:3) | Centre point, 20 g dose | Schmieder et al.4 |\n| Extraction yield | About 20% typical; 17–18% at < 10–15 s; 19–20% at about 30 s | 20 g → 40 g, 9 bar | Smrke et al.5 |\n\nFrom the dissolved solids above, the extraction yields at the centre point work out at 14.6%, 19.4% and 21.0%, and the TDS at 14.6%, 9.7% and 7.0% (our own arithmetic).4 The beverage per gram of coffee in the other recipes works out at about 3.6 mL/g (7 g → 25 mL)3, 3.7 mL/g (16 g → 2 × 30 mL)6 and 1.75 g/g (18 g → 31.5 g)7 (our own arithmetic).\n\n## The science of the ratio\n\nEspresso is a percolation: fresh water keeps passing through the bed, so the extract changes over the shot. In a 2023 flow-controlled study, the concentration of every measured compound was highest in the first drops and fell exponentially as more espresso was collected.4 Trigonelline and total dissolved solids fell fastest, then 5-CQA (5-caffeoylquinic acid, the main chlorogenic acid), then caffeine.4\n\nThis is why the ratio drives both strength and yield. Each extra gram in the cup is weaker than the last, so TDS falls; it still adds dissolved coffee, so the yield keeps rising.4 In that study, going from 1:2 to 1:3 added far less dissolved coffee than going from 1:1 to 1:2: 0.31 g against 0.96 g (our own arithmetic from its table).4\n\nA coffee science textbook explains the flavour side. Very soluble compounds – caffeine, sugars, organic acids – come out in the first seconds.1 Less soluble bitter compounds, such as phenylindanes, keep coming out over time.1 In its account, this is why long cups tend to be both stronger and more bitter, and why the profile moves from sweet–acidic to bitter–harsh as extraction goes on.1 Aroma follows a similar pattern by polarity: in a 2016 on-line study, the most polar compounds came out within the first seconds, while part of the least polar ones was still coming out at 25 s.7\n\n**Flow and pressure.** In the 2023 study, a slower flow gave higher concentrations early in the shot, and a faster flow lowered the mass of every compound in the cup.4 Flow rate had the strongest effect of the three settings tested; a finer grind and a higher temperature made it stronger.4 The authors relate faster flow to higher pressure through Darcy’s law, and note that earlier pressure studies also found less in the cup at higher pressure.4 Their flow-controlled shots ran at measured pressures of 2.6–8.4 bar, below the conventional 9 bar.4 According to a textbook, a higher pressure was linked to a more viscous espresso with more body in an earlier study.1\n\n**Pressure and flow profiles.** According to a textbook, newer machines let the barista control flow or vary pressure during the shot, to reproduce chosen extraction profiles.1 The 2023 study used one such machine for flow control.4 No study opened for this entry compared the flavour of different pressure or flow profiles.\n\n**Grind and the bed.** In a 2020 study combining a model with experiments, the model assumed even flow and predicted that yield falls steadily as the grind gets coarser.9 Measured yields instead peaked, with lower yields at very fine settings too.9 The authors attribute this to uneven flow at fine settings, which wastes coffee and makes shots less reproducible, and they outline a procedure to avoid it.9 In a 2024 study, adding fines lowered the bed’s permeability, slowed the flow and lengthened the shot.5 In a 2020 study, smaller particles extracted more caffeine per cup: more at 200–300 µm than at 500–1,000 µm, in every basket tested.10\n\n**Grinders differ.** According to the grinding chapter of a coffee science textbook, different grinders need different settings to give the same flow time at the same ratio.2 In its account, a grinder with a wide particle size distribution over-extracts the fines and under-extracts the coarse particles. The cup is then both more bitter and more acidic, at a lower overall yield.2 A recipe moved to another grinder therefore needs dialling in again.\n\n## Signs of under- and over-extraction\n\nA coffee science textbook describes brews below a long-used yield range as under-extracted, too sweet and acidic, and brews above it as over-extracted, bitter and astringent.1 It notes that optimal yields outside this range have been reported for several methods.1 The extraction yield entry gives the range and its origin. A 2020 sensory study that spanned the classic brewing control chart used drip coffee.12 No espresso-specific sensory map was found among the sources opened for this entry.\n\nA 2011 review lists visual signs in the crema:8\n\n- **Pale crema:** under-extracted, probably from too coarse a grind, too cool water or too short a time.8\n- **Very dark crema with a white spot in the middle:** grind too fine or too much coffee.8\n- **White foam with large bubbles:** over-extracted with water that was too hot.8\n- **Only a white spot in the centre:** over-extracted because the shot ran too long.8\n\nThe same review notes that such readings of crema rest on decades of trial and error more than on objective measurement.8 Tasting and, where possible, measuring remain the checks the brewing textbook recommends.1\n\n**Uneven extraction** is a defect of its own. In the 2020 grind study, uneven flow at fine settings lowered the average yield and made shots less reproducible.9 Channelling, where water takes easy paths through the bed, is one form of uneven flow. The puck preparation entry covers its causes.\n\n## Open questions\n\n- **Espresso control chart.** A 2020 sensory study across the range of the classic control chart used drip coffee.12 No study opened for this entry mapped espresso flavour or consumer liking across ratio, TDS and extraction yield.\n- **Temperature.** Studies disagree on how much brew temperature changes an espresso (see Contested).4,7 No study opened for this entry fixed strength and yield while varying espresso temperature.\n- **Profiles.** Some machines vary pressure or flow during the shot, but no controlled sensory study of profiles was opened for this entry.1\n- **Less coffee per cup.** Two studies point to using less coffee: one by avoiding uneven flow, one by finer particles and basket design.9,10 Whether a smaller dose keeps the flavour was not tested in the abstracts opened for this entry.\n- **Café rules of thumb.** No study opened for this entry tested the target times and ratios used in café practice.\n\n## Key studies\n\n
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Schmieder et al., 2023 – Flow, grind and temperature. Collected ten fractions from each flow-controlled shot of a 20 g dose and calculated the cup for ristretto, espresso and lungo. Flow rate had the strongest effect of the three settings, but all were minor next to the amount of beverage collected.

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Foods 12(15), 2871 · doi:10.3390/foods12152871

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Smrke et al., 2024 – Fines in espresso. Followed extraction over shots of 20 g to 40 g at different grind settings, with sieved fines added. Short shots already reached most of the yield, and fines acted mainly by slowing the flow through the bed.

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Scientific Reports 14, 5612 · doi:10.1038/s41598-024-55831-x

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Cameron et al., 2020 – Uneven flow and grind. Compared a model of espresso extraction with measured shots. Yield peaked at an intermediate grind instead of rising steadily with fineness, which the authors trace to uneven flow; they propose a more reproducible procedure.

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Matter 2(3), 631–648 · doi:10.1016/j.matt.2019.12.019

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Andueza et al., 2007 – Coffee to water ratio. Brewed espressos from arabica and robusta, conventionally roasted and torrefacto, at different amounts of coffee per cup. Sensory attributes such as bitterness and astringency pointed to 6.5 or 7.5 g per 40 mL for conventional roasts.

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Journal of the Science of Food and Agriculture 87(4), 586–592 · doi:10.1002/jsfa.2720

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Gloess et al., 2013 – Espresso and lungo. Compared espressos and lunghi from semi-automatic and fully automatic machines with other brew methods. Lunghi extracted more efficiently and held as much per cup as espressos, while espressos were more concentrated.

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European Food Research and Technology 236, 607–627 · doi:10.1007/s00217-013-1917-x

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