{ "id": "extraction-yield-and-tds", "url": "https://coffearium.org/entries/extraction-yield-and-tds/", "license": "CC-BY-4.0", "title": "Extraction yield and TDS", "summary": "How strong a coffee is (total dissolved solids) and how much of the grounds ended up in it (extraction yield) – the two numbers behind the brewing control chart, how to measure them and what they say about flavour.", "domain": "extraction", "kind": "Concept", "stage": "brew", "topics": [ "science", "history" ], "topicSections": {}, "lang": "en", "status": "verified", "reviewer": "Coffearium verification pass", "lastVerified": "2026-10-10T00:00:00.000Z", "updated": "2026-10-10T00:00:00.000Z", "brief": [ "TDS (total dissolved solids) is the strength of a brew – the share of its mass that is dissolved coffee.8", "Extraction yield is the share of the ground coffee (the dose) that ended up dissolved in the brew.8,2 It is calculated as TDS × beverage mass ÷ dose.1,6", "The Golden Cup Standard of the Specialty Coffee Association (SCA), the “ideal” box of a control chart dating from the 1950s, spans 1.15–1.35% TDS and 18–22% extraction.1,2", "In one 2020 sensory study of drip coffee, TDS had the larger effect on flavour and extraction yield a smaller but noticeable one.1", "Consumers do not all prefer the “ideal” box. A 2023 study found two preference groups and proposed a new Sensory and Consumer chart to replace the classic one.2" ], "quickFacts": [ { "label": "TDS", "value": "Mass of dissolved coffee ÷ mass of beverage, in %" }, { "label": "Extraction yield (EY, PE)", "value": "Mass of dissolved coffee in the brew ÷ dose of ground coffee, in %" }, { "label": "Core equation", "value": "EY = TDS × beverage mass ÷ dose" }, { "label": "Golden Cup Standard (SCA)", "value": "1.15–1.35% TDS, 18–22% extraction" }, { "label": "SCA home-brewer test", "value": "1.15–1.55% TDS at 55 g coffee per kg water" }, { "label": "Soluble share of roasted coffee", "value": "About 30% (about one third)" }, { "label": "Liquid held by spent grounds", "value": "About 2.1 g/g (drip); 2.48 ± 0.19 g/g (immersion study)" }, { "label": "Measured with", "value": "Coffee refractometer (routine); oven drying (reference)" } ], "aka": [ "Extraction percentage", "Percent extraction", "Brew strength" ], "linkTerms": [ "extraction yield", "total dissolved solids", "brew strength" ], "related": [ "roasting", "freshness-and-storage", "water-for-coffee", "brew-methods", "espresso", "grinding", "particle-size-and-fines", "cupping", "coffee-capsules", "what-extraction-is", "extraction-variables", "brew-ratio-and-strength", "brewing-control-chart", "measuring-water" ], "contested": [ "Target strength for filter coffee: the SCA Golden Cup Standard gives 1.15–1.35% TDS with 18–22% extraction1, while the SCA’s own home-brewer standard (SCA 310-2021) sets a test target of 1.15–1.55% TDS at 55 g coffee per kg water.8 The two documents serve different purposes – a quality target and an appliance test.", "Validity of the “ideal” box: a 2017 textbook chapter calls 18–22% a range “generally considered” good for a long time, while noting that optimal yields outside it, mostly higher, have been reported4; the authors of the 2023 Sensory and Consumer chart call the classic “ideal” point misleading and possibly inaccurate, because preferences split into two consumer groups.2", "Role of brew temperature: a coffee science textbook states that higher temperature raises the solubility of most coffee compounds and favours less polar, bitter ones4; yet at fixed TDS and extraction, brews made at 87, 90 and 93 °C did not differ appreciably in sensory profile1, and in full immersion the equilibrium constant did not change between 80 and 99 °C.3", "Extraction yield of immersion brews: computed from beverage mass, it depends on how much liquid stays in the grounds; at equilibrium, a model and experiments put it at about 21% over a wide range of brew ratios, and oven drying of the grounds underestimates it.3 A comparison based on oven-dried total solids found 26% for a French press.5 Method and definition differ, so the figures are not directly comparable.", "Bitterness at higher strength: a coffee science textbook states that, at the same yield, more coffee per litre gives a stronger brew but not a more bitter one4; an SCA magazine article by the UC Davis research group reports that, in general, bitterness increased with both TDS and extraction yield in its drip-coffee studies.9" ], "corrections": [], "sources": [ { "id": "s1", "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": "The chart’s central region, which spans TDS values of 1.15–1.35% and PE values of 18–22%, is denoted as “ideal”", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s2", "title": "A new Coffee Brewing Control Chart relating sensory properties and consumer liking to brew strength, extraction yield, and brew ratio", "authors": "Guinard, J.-X.; Frost, S.; Batali, M.; Cotter, A.; Lim, L. X.; Ristenpart, W. D.", "year": 2023, "publisher": "Journal of Food Science 88(5), 2168–2177", "url": "https://ift.onlinelibrary.wiley.com/doi/10.1111/1750-3841.16531", "doi": "10.1111/1750-3841.16531", "tier": "A", "quote": "we propose that this new Sensory and Consumer BCC replace the classic BCC.", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s3", "title": "An equilibrium desorption model for the strength and extraction yield of full immersion brewed coffee", "authors": "Liang, J.; Chan, K. C.; Ristenpart, W. D.", "year": 2021, "publisher": "Scientific Reports 11, 6904", "url": "https://www.nature.com/articles/s41598-021-85787-1", "doi": "10.1038/s41598-021-85787-1", "tier": "A", "quote": "E is approximately 21% over a wide range of brew ratios", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s4", "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": "Yields between 18% and 22% have been generally considered as a good range for quite a long time, when it comes to brew quality.", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s5", "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": "The maximum extraction yield was given by Bia extraction (31.2 %), followed by Bo (26 %).", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s6", "title": "Extraction of single serve coffee capsules: linking properties of ground coffee to extraction dynamics and cup quality", "authors": "Eiermann, A.; Smrke, S.; Guélat, L.-M.; Wellinger, M.; Rahn, A.; Yeretzian, C.", "year": 2020, "publisher": "Scientific Reports 10, 17079", "url": "https://www.nature.com/articles/s41598-020-74138-1", "doi": "10.1038/s41598-020-74138-1", "tier": "A", "quote": "The concentration of coffee in the filtered brew (0.45 µm filter) was analysed using a VST LAB Coffee III refractometer (VST inc., Tulsa, US).", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s7", "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": "2026-10-10T00:00:00.000Z" }, { "id": "s8", "title": "SCA Standard 310-2021 Home Coffee Brewers: Specifications and Test Methods", "authors": "Specialty Coffee Association", "year": 2021, "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/s/SCA_Standard_310-2021.pdf", "tier": "A", "quote": "For this standard, target extraction parameters shall be a brew strength of 1.15-1.55% at the standard brew ratio.", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s9", "title": "Towards a New Brewing Chart", "authors": "Frost, S.; Batali, M.; Guinard, J.-X.; Ristenpart, W. D.", "publisher": "Specialty Coffee Association, 25 Magazine, Issue 13", "url": "https://sca.coffee/sca-news/25/issue-13/towards-a-new-brewing-chart-xpj8t", "tier": "B", "quote": "Here we can see more clearly that in general the trend is that bitterness increases with both TDS and PE.", "accessed": "2026-10-14T00:00:00.000Z" }, { "id": "s10", "title": "Coffee, Decoded: The Science of “Dialling-In”", "authors": "Carmichael, L. (column hosted by Giuliano, P.)", "publisher": "Specialty Coffee Association", "url": "https://sca.coffee/sca-news/coffee-decoded-14-dialling-in", "tier": "B", "quote": "Lockhart developed a hypothesis that coffee beverage quality could be estimated by measuring the Total Dissolved Solids (TDS)", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s11", "title": "The Complexity of Coffee", "authors": "Illy, E.", "year": 2002, "publisher": "Scientific American (June 2002)", "url": "https://www.scientificamerican.com/article/the-complexity-of-coffee/", "tier": "C", "quote": "The resulting concentrated liquor contains not only soluble solids but also a diverse array of aromatic substances in a dispersed emulsion of tiny oil droplets, which together give espresso its uniquely rich taste, smell and “mouthfeel.”", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s12", "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 optimum total dissolved solids (TDS) value of 150 mg/L is stated; however, the standard method of determining TDS using a conductivity meter has an uncertainty of approximately 30%.", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s13", "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.", "accessed": "2026-10-10T00:00:00.000Z" }, { "id": "s14", "title": "Crema – Formation, Stabilization, and Sensation", "authors": "Folmer, B.; Blank, I.; Hofmann, T.", "year": 2017, "publisher": "In: Folmer, B. (ed.), The Craft and Science of Coffee, Academic Press, ch. 17, pp. 399–417", "url": "https://doi.org/10.1016/B978-0-12-803520-7.00017-7", "doi": "10.1016/B978-0-12-803520-7.00017-7", "tier": "B", "quote": "Certainly, espresso is a complex polyphasic liquid composed of (1) emulsion of oil droplets, (2) suspension of solid particles, and (3) effervescence of gas bubbles that evolve into a foam (Illy and Viani, 2005).", "accessed": "2026-10-10T00:00:00.000Z" } ], "markdown": "## What extraction is\n\nBrewing moves material from the ground coffee into water. Some of it dissolves. A coffee science textbook and a magazine article describe oil droplets and fragments of the cell structure being carried along as well in espresso.11,14 According to a 2021 model study, only part of a roasted bean can dissolve: typically about 30%, or about one third of its mass.3\n\nA coffee science textbook describes how compounds dissolve at different speeds. Very soluble compounds – caffeine, sugars, organic acids – come out in the first seconds of a brew.4 Less soluble bitter and astringent compounds keep coming out over the whole brew.4 In the textbook’s account, the balance of the cup therefore shifts as extraction goes on: from sweet and acidic towards bitter, harsh and astringent.4 The textbook gives this as the reason why “how much was extracted” is used as a quality measure.4\n\n## Two numbers: strength and yield\n\n**TDS (total dissolved solids)** is the strength of the brew. It is the amount of dissolved coffee in the beverage, expressed in per cent (or parts per million).8 It is usually estimated with a coffee refractometer, a small instrument that reads a drop of brew.8 A filter coffee at 1.30% TDS holds 1.30 g of dissolved coffee in every 100 g of beverage.\n\n**Extraction yield** (also called percent extraction, PE) is the share by mass of the ground coffee that has dissolved into the brew.2,8 It describes how much of the grounds has dissolved, not how strong the cup is.\n\nThe two are different things. According to a coffee science textbook, a strong coffee can come from little water and a lot of coffee, or the reverse.4 In either case, it may not taste right.4 In the textbook’s account, more coffee per litre at the same yield gives a stronger brew, not a more bitter one.4 The stronger brew simply contains more solids.4 Sensory research on drip coffee reports that, in general, bitterness rises with strength as well (see Contested).9\n\n**Ratios.** Three masses are involved: the dose of dry coffee, the water poured in and the beverage collected.\n\n- The **brew ratio** (brewing ratio) relates water to coffee. Researchers write it as water mass ÷ coffee mass.2,3 The Specialty Coffee Association (SCA) home-brewer standard gives it in grams of coffee per kilogram of fresh water, with 55 g/kg as its test ratio.8\n- In this entry, the **beverage ratio** means beverage mass ÷ dose: what is in the cup, not what went into the brewer. It is the ratio used in the extraction-yield formula below.1,6 One espresso study gives its recipe this way: 20 g of coffee to 40 g of beverage.7\n- The difference between the two is mostly **retained liquid**: the spent grounds hold back brew. In a 2023 drip-coffee study, this “liquid retention ratio” was about 2.1 g per gram of coffee.2 In one set of immersion brews it averaged 2.48 ± 0.19.3\n\n## The core equation\n\nExtraction yield is calculated from the TDS, the mass of beverage and the dose:1,6\n\n**EY (%) = TDS (%) × beverage mass (g) ÷ dose (g)**\n\nThe worked examples below are our own arithmetic. They assume a filtered sample (dissolved solids only), a dose weighed dry, and the beverage weighed in the cup.\n\n| Brew | Dose | Beverage | TDS | Extraction yield |\n|---|---|---|---|---|\n| Filter, 55 g per 1,000 g water | 55 g | 896 g | 1.30% | 1.30% × 896 ÷ 55 = **21.2%** |\n| Espresso, 1:2 | 18 g | 36 g | 10.0% | 10.0% × 36 ÷ 18 = **20.0%** |\n| Espresso, same coffee, lower TDS | 18 g | 36 g | 9.0% | 9.0% × 36 ÷ 18 = **18.0%** |\n\nIn the filter example, the 896 g of beverage is not measured but estimated. The grounds retain about 2.1 g per gram of coffee.2 Taking this from 1,000 g of water leaves about 885 g of water, which carries 1.3% dissolved coffee. Weighing the beverage avoids this estimate.\n\nWithout a beverage weight, yield can be estimated from the water and the retention ratio. For drip brewing, the 2023 chart paper uses the formula below:\n\n**PE = TDS ÷ (1 − TDS) × (Rbrew − Rabs)**\n\nHere Rbrew is water mass ÷ coffee mass, and Rabs ≈ 2.1 is the retained liquid.2\n\nOn the chart, each brew ratio marks a diagonal line.2 By this formula, the line is nearly straight and runs through the origin (our own arithmetic). So at a fixed ratio, a higher TDS always means a higher yield.\n\n
\n
\n
    \n
  1. Water in. Its mass is what water-based formulas start from.2
    2. \n
  2. Dry coffee dose. Only part of it can dissolve: typically about 30% of roasted coffee, in a 2021 model study.3
    3. \n
  3. Retained liquid. Brew held back in the spent grounds: about 2.1 g per gram of coffee in a drip study.2 In one set of immersion brews, 2.48 ± 0.19 g/g.3
    4. \n
  4. Spent grounds. The coffee that did not dissolve.3
    5. \n
  5. Beverage. Water plus dissolved coffee; its strength is the TDS.1,8
    6. \n
\n

Which mass each formula uses

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Where the coffee goes in a drip brew: water and dose in; beverage, retained liquid and spent grounds out. Schematic, not to scale.
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\n\n## Measuring TDS\n\n**Refractometer.** A coffee refractometer estimates TDS from the refractive index of a drop of brew: how strongly the liquid bends light.8 Research labs cool the sample to room temperature before measuring.1,3 One immersion study zeroed the instrument with distilled water.3 For espresso, labs pass the brew through a 0.45 µm filter first.6,7\n\nThe SCA home-brewer standard (SCA 310-2021) specifies a coffee refractometer for the brew strength of every sample.8 Its separate test checks how evenly the grounds are extracted.8 That test requires at least three readings, averaged, with the refractometer well rinsed with distilled water.8\n\n**Oven drying** is the reference method: a weighed sample of brew is dried to constant weight, and the residue is weighed.5 A 2013 comparison of nine brew methods dried its samples at 105 °C.5 Oven drying measures total solids, or dry matter, not only dissolved solids.4,5 Refractometer readings are checked against oven drying1 or against solutions of known concentration.3\n\n**Water “TDS” is not coffee TDS.** According to a coffee science textbook, the handheld “TDS meters” used for water measure electrical conductivity.12 They convert it with a factor that depends on the minerals present, so the result is only a rough estimate.12 Coffee TDS from a refractometer is a different measurement.\n\n## The brewing control chart\n\nThe control chart puts the two numbers on one page. Extraction yield runs along one axis, TDS along the other, and diagonal lines mark brew ratios.2 Every brew is a point on it. According to an SCA magazine article by the chart’s researchers, all its quantitative relations follow from conservation of mass.9 In their account, the sensory zones drawn on it are what set it apart.9\n\n**History.** The chart was developed in the 1950s.2 In 1957, Ernest E. Lockhart of the Coffee Brewing Institute published *The Soluble Solids in Beverage Coffee as an Index to Cup Quality*.1,2 The publication proposed that measuring TDS and calculating extraction could predict flavour and quality.1,10 It identified TDS near 1.25% and extraction near 20% as “ideal”.3 The chart was later carried in the Coffee Brewing Handbook of the Specialty Coffee Association of America.2,4 Studies from 2020 and 2023 describe it as the basis of vocational training in the coffee industry.1,2\n\n**The classic zones.** The classic chart is divided into nine regions. Along the TDS axis they are labelled “strong” and “weak”.1 Along the extraction axis, the flavour labels are reduced to “under-developed” and “bitter”, usually called under- and over-extracted.1,4,9 The central region – 1.15–1.35% TDS and 18–22% extraction – is the “ideal”, also known as the SCA Golden Cup Standard.1 A coffee science textbook describes brews below 18% as under-extracted (too sweet and acidic) and brews above 22% as over-extracted (bitter and astringent).4\n\n**Sensory research from 2020.** In studies published from 2020, a University of California, Davis (UC Davis) group brewed drip coffee to fixed points across the chart.1,2 The group tested the brews with trained panels and consumers.1,2 The findings:\n\n- In a 2020 study, TDS had the greatest impact on the sensory profile; extraction yield had a lesser but noticeable one.1\n- According to the group’s SCA magazine article, bitterness in general rose with both TDS and extraction, as the classic chart implies (see Contested).9\n- The same article reports that sourness rose with TDS but fell with extraction, peaking at high TDS and low yield.9 On the 2023 chart, sour, citrus and red-fruit notes sit in that corner; bitterness, astringency and roasted notes at high TDS and high yield.2\n- According to two SCA articles, sweetness was highest at low TDS and low yield.9,10\n- In the 2023 study, consumers split into two groups. The larger (57%) liked low-TDS coffees best, with liking peaking at 18% extraction. The other (43%) liked two different kinds of coffee equally: low yield with medium to high TDS, and high yield with medium TDS.2\n\nThe authors call the classic “ideal” point misleading and possibly inaccurate. They propose a new Sensory and Consumer control chart to replace the classic one.2 The new chart shows only drip coffee; it does not show the effects of variety, origin, roast or brewing variables.2\n\n### Plotting a brew on the chart\n\nEnter your dose, the weight of the beverage (or the water) and the TDS you measured. The tool calculates the extraction yield with the formulas above and places your brew on the chart.\n\n
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Interactive brewing control chart: extraction yield against TDS, with the SCA Golden Cup box1 and the SCA home-brewer test band.8 It also shows the flavour and consumer regions of the 2023 Sensory and Consumer chart.2,9 Enter dose, beverage or water mass and a TDS reading to place a brew. Brew-ratio lines are calculated, not measured.2
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\n\n## What changes extraction yield\n\nExtraction yield is an outcome, and many settings feed into it. According to a coffee science textbook, these settings interact: a finer grind both speeds extraction and lengthens flow time, so the effects multiply.4\n\n- **Grind.** According to the textbook, finer particles expose more surface and extract more efficiently; too fine a grind can block flow.4 In a 2020 espresso study, measured yield peaked at an intermediate grind setting and dropped again at the finest settings.13 In a 2020 capsule study, a larger share of fines (particles below 100 µm) lengthened the extraction time.6\n- **Time and volume.** In one espresso study, shots of under 10–15 s already reached 17–18% extraction.7 The best flavour for that coffee (one panellist) came at about 30 s and 19–20%.7\n- **Ratio.** In percolation, water flows through a bed of grounds, as in drip brewing. According to the textbook, the balance in the cup keeps changing as more water passes through the bed.4 In full immersion, all the water steeps with all the coffee. In a 2021 immersion study, the brew approached an equilibrium: changing the ratio changed the TDS, but barely the yield.3\n- **Temperature.** According to the textbook, solubility generally rises with temperature, and hotter water favours less polar, bitter compounds (polar compounds mix readily with water).4 Its sensory effect at a fixed TDS and yield was small in one drip study (see Contested).1\n- **Water.** According to the textbook, its hardness, acidity and cation composition can directly influence the sensory result of the extract.4 Cations are the positively charged mineral ions in water. The water entry covers this.\n- **Freshness.** A coffee science textbook advises letting freshly roasted beans stabilise while they release gas.4 The freshness entry covers how this affects brewing.\n\n## Drip and immersion\n\n**Drip (percolation).** Water keeps passing through the bed. According to a coffee science textbook, the composition of the brew changes as long as it does.4 Beverage mass is easy to weigh, and the core equation applies directly.1 In a 2023 drip study, the grounds kept about 2.1 g of liquid per gram, which never reaches the cup.2\n\n**Full immersion.** All the water sits with all the coffee. In a 2021 model, the dissolved coffee spreads between liquid and grounds until it reaches equilibrium, a steady balance.3 The same study’s model and experiments put the yield at equilibrium at about 21% over a wide range of brew ratios.3 TDS was roughly inversely proportional to the brew ratio: a higher ratio gave a weaker brew.3 The authors conclude that immersion gives precise control of strength through the ratio but little control of yield.3 On the control chart, changing the ratio of an immersion brew moves it up or down, not sideways.3\n\nThat has a consequence for the arithmetic. The spent grounds of an immersion brew hold retained brew with dissolved solids, and the equilibrium calculation counts this coffee as extracted.3 Calculating yield from the beverage poured off therefore gives a lower number than the true extraction (see Deep dive).\n\n\n\n## Mass balance and retained liquid\n\nLet *m*c be the dry dose, *m*w the water added, *m*b the beverage collected and *m*r the liquid retained in the spent grounds. Extraction yield is defined as the mass of coffee that has dissolved into the liquid, divided by the dose.3 Three versions of the calculation are in use:\n\n1. **Beverage-based (percolation, espresso).** EY = TDS × *m*b ÷ *m*c.1,6 It counts only what reached the cup.\n2. **Water-based with retention (drip).** EY = TDS ÷ (1 − TDS) × (*m*w/*m*c − Rabs), with Rabs ≈ 2.1.2 The factor 1 ÷ (1 − TDS) converts from water to liquid mass; at filter strength it changes the result by about 1% (relative; our own arithmetic).\n3. **Equilibrium (full immersion).** The model counts all the water added, including the brew retained in the grounds: E = TDS ÷ (1 − TDS) × *m*w/*m*c. This yield cannot be measured directly; it is related to the measured TDS and brew ratio.3\n\n**Worked comparison (our own arithmetic).** Take 15 g of coffee steeped to equilibrium in 250 g of water, reading 1.35% TDS, and assume, as the equilibrium formula does, that the retained liquid is as strong as the beverage. The liquid holds 250 ÷ (1 − 0.0135) = 253.4 g, of which 3.42 g is coffee: a true yield of 22.8%. If the grounds keep 2.48 g of liquid per gram (the immersion study mean3), 37.2 g stays behind and 216.2 g is poured off. The beverage-based formula then gives 1.35% × 216.2 ÷ 15 = 19.5%. The same brew differs by about three points depending on the formula.\n\n**Oven-dried grounds.** Yield can also be measured from the other side: dry and weigh the spent grounds. According to the immersion study, the spent grounds always hold some retained brew with dissolved solids, so the yield measured this way is always lower than the true value.3 In that study it rose with brew ratio and levelled off near 20%.3\n\n## Espresso and filter: dissolved versus total solids\n\nAccording to two chapters in a coffee science textbook and a magazine article, an espresso contains soluble solids but also an emulsion of tiny oil droplets and fragments of cell structure.11,14 The textbook’s brewing chapter states that mouthfeel depends partly on suspended fines, particularly in French press and espresso; filter paper absorbs oil very efficiently, so filter brews are low in fat.4\n\nThis matters for measurement. A refractometer reading is meant to give dissolved solids, and in research practice espresso is filtered (0.45 µm) before reading.6,7,8 Oven drying, by contrast, includes everything that is not water.5 Total-solids yields and refractometer yields should not be mixed in one comparison.\n\nEspresso is also far stronger. In one comparison, espressos from three machines held more than 4% total solids, moka pot coffee 2.13%, French press 1.43% and filter coffee 1.03%.5 Per cup, an espresso and a lungo held about the same total solids.5 Espresso yields are nevertheless similar to filter yields: in one 2024 study, around 20% of the dry coffee dissolved in a typical shot.7 Because espresso uses so little liquid, a few grams of beverage move the yield: in the 1:2 example above, 2 g more beverage at the same TDS adds 1.1 points (our own arithmetic). The 2024 study weighed the shot continuously with a load cell.7\n\n
\n
\n
Extraction yields reported for different brew methods, with the Golden Cup range for reference.1,3,5,7 The 2013 nine-method comparison measured oven-dried total solids, the others refractometric dissolved solids; compare within a source.
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\n\n## Limits of extraction yield as a quality measure\n\nAccording to a coffee science textbook, extraction yield is a single number for a mixture of many compounds that dissolve at different rates.4 In its account, the balance between the extracted compounds also strongly affects quality, next to strength and yield.4 Human perception adds a further complication: the textbook describes the response to each flavour compound as a sigmoid curve, so a higher concentration may raise one note and not another whose receptors are already saturated.4\n\nThe sensory studies support caution. In one drip study, TDS drove most of the sensory variation, with yield secondary.1 In one study of 43 capsule coffees, sensory quality in the cup was not correlated with the technical properties of the grounds.6 The classic zone boundaries also imply sharp steps. According to the UC Davis group’s SCA magazine article, most coffee experts could not tell apart brews just either side of a zone boundary, although the chart puts them in different zones.9 The textbook describes tasting as the key control; a refractometer guides adjustments and makes brews repeatable.4\n\n## Measurement uncertainty\n\n- **Refractometer.** One immersion study calibrated its coffee refractometer against solutions of known concentration made from instant coffee and describes the resulting calibration curve as excellent; it gives no correlation coefficient for the calibration.3 One capsule study calibrated its refractometer with a soluble-coffee sample.6 Labs cool samples to room temperature and filter espresso before reading.1,3,6 The sources opened for this entry give no instrument precision specification.\n- **Uncertainty propagation (our own arithmetic).** EY is a product and quotient, so relative uncertainties add. If TDS is read to ±0.02 percentage points at 1.30% (±1.5%) and both masses to ±1 g on 55 g and 896 g (±1.8% and ±0.1%), the yield carries about ±3.4% relative uncertainty: 21.2% ± 0.7 points. These precisions are assumptions for illustration, not instrument specifications.\n- **Which formula.** For the same immersion brew, beverage-based and equilibrium formulas can differ by about three points (see Mass balance). Stating the formula matters as much as the reading.\n\n## Reference values\n\n| Parameter | Value reported | Context | Source |\n|---|---|---|---|\n| Golden Cup Standard (SCA) | 1.15–1.35% TDS; 18–22% extraction | Central “ideal” region of the classic chart | Batali et al.1 |\n| “Good” yield range | 18–22% | Long-standing industry range; higher optima reported for some methods | Mestdagh et al.4, Batali et al.1 |\n| Lockhart’s “ideal” | TDS near 1.25%; extraction near 20% | Original work, 1957 | Liang et al.3 |\n| SCA home-brewer test | 1.15–1.55% TDS at 55 g coffee per 1.000 kg water; slurry 90–96 °C | Appliance certification (SCA 310-2021) | SCA8 |\n| UC Davis design points | TDS 1.0, 1.25, 1.5%; extraction 16, 20, 24% | Drip coffee; basis of the 2023 chart | Guinard et al.2 |\n| Consumer segments | 57% preferred low TDS (peak at 18% extraction); 43% two optima | Drip coffee | Guinard et al.2 |\n| Soluble share of roasted coffee | About 30% | Typical maximum extraction | Liang et al.3 |\n| Liquid retention ratio, drip | ≈2.1 g per g coffee | Spent moist grounds | Guinard et al.2 |\n| Liquid retention ratio, immersion | 2.48 ± 0.19 g per g coffee | Immersion study | Liang et al.3 |\n| Equilibrium yield, immersion | About 21% (20.70 ± 1.08%, calculated from measured TDS) | Brew ratios ≥3, 80–99 °C | Liang et al.3 |\n| Yield, cupping-style brews | 23.9% (caffeinated); 22.2% (decaf) | Immersion at equilibrium | Liang et al.3 |\n| Filter coffee | 1.03% total solids; 19% yield | 100 g coffee, 1,800 mL; oven-dried | Gloess et al.5 |\n| French press | 1.43% total solids; 26% yield | 27.5 g coffee, 500 mL; oven-dried | Gloess et al.5 |\n| Moka pot | 2.13% total solids; 31.2% yield | 7.5 g coffee, 110 mL; oven-dried | Gloess et al.5 |\n| Espresso, three machines | > 4% total solids | 30 mL shots; oven-dried | Gloess et al.5 |\n| Espresso yield | About 20% typical; 17–18% at < 10–15 s; 19–20% at about 30 s | 20 g coffee to 40 g beverage, 9 bar | Smrke et al.7 |\n| Capsule beverage mass | 40.1 ± 0.3 g | 43 capsule coffees, one machine | Eiermann et al.6 |\n| Water-to-coffee ratio by method | Drip ≈13–20; French press ≈15–20; espresso 3.5–6; moka ≈9–15 mL/g | Typical ranges | Mestdagh et al.4; consistent with doses in Gloess et al.5 |\n| Brew temperature tested | 87, 90, 93 °C – no appreciable sensory effect at fixed TDS and yield | Drip coffee | Batali et al.1 |\n| Refractometer vs known TDS | Calibration curve described as excellent; no coefficient reported | Instant-coffee standards | Liang et al.3 |\n| Sample preparation | Cooled to room temperature; espresso filtered at 0.45 µm | Research practice | Batali et al.1, Liang et al.3, Eiermann et al.6 |\n\nThe ratios in the 2013 nine-method comparison work out at 18 mL/g (filter), 18 mL/g (French press), about 15 mL/g (moka) and about 4 mL/g (espresso, two 30 mL shots from 16 g) – our own arithmetic from the doses and volumes in the paper.5\n\n## What over-extraction means chemically\n\nOver- and under-extraction are shifts in what has dissolved, not only in how much. According to a coffee science textbook, very soluble, polar compounds – caffeine, N-methylpyridinium, sugars, organic acids – are extracted almost completely early; a low yield therefore gives a cup dominated by them, with a sweet–acidic profile.4 In the same account, less soluble bitter and astringent compounds – phenylindanes, chlorogenic acid lactones, diketopiperazines and conjugated amides – come out later; phenylindanes almost continuously.4 The textbook describes the phenylindanes as giving a harsh, lingering bitterness, and the chlorogenic acid lactones a more pleasant, coffee-like bitterness.4 Among aroma compounds, it reports that guaiacol, 4-ethylguaiacol and 4-vinylguaiacol increase during extraction and correlate with off-flavours linked to over-extraction.4\n\nThe textbook also describes aroma as behaving in the opposite way to taste in one respect: highly polar, highly volatile odorants come out at the very beginning of the extraction, so their share falls as extraction continues.4 It gives one practical remedy for over-extraction in filter brewing: stop percolation early and add hot water to the brew (bypass), instead of letting all the water pass through the grounds.4\n\n## Open questions\n\n- **Optimal yield range.** According to a 2017 textbook chapter, optimal yields outside 18–22%, mostly higher, have been reported for several methods. In its account, roast colour, coffee quality and extraction technique may shift the optimum, and good research on this question remains to be done.4\n- **Espresso and the chart.** The 2023 chart covers drip coffee only.2 No comparable sensory and consumer map for espresso was found among the sources opened for this entry.\n- **Consumer preference beyond one population.** The consumer data behind the 2023 chart come from one university research programme, and the consumers were mainly young adults in Northern California.2 No study opened for this entry tested whether the two preference segments exist in other countries or coffee cultures.\n- **Uneven extraction.** In a 2020 study, espresso models predicted yield falling steadily with coarser grind, but experiments showed a peak, which the authors attribute to uneven flow at fine settings.13 A single average yield hides how unevenly the bed was extracted.\n- **Immersion profiles.** Since immersion yield is close to fixed at equilibrium, reaching the low-yield, high-TDS corner (sour, citrus) may require stopping the brew early.3\n\n## Key studies\n\n
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Batali et al., 2020 – Temperature at fixed strength and yield. Drip-brewed coffee to nine points across the classic control chart at 87, 90 and 93 °C, adjusting grind and time to hit each target. Trained panellists found that TDS shaped the sensory profile most and extraction yield less, while brew temperature had almost no effect once TDS and yield were fixed.

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Scientific Reports 10, 16450 · doi:10.1038/s41598-020-73341-4

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Guinard et al., 2023 – A new control chart. Combines three UC Davis studies of drip coffee into a Sensory and Consumer Brewing Control Chart that shows where each flavour attribute peaks and where two consumer segments find their optimum. The authors argue that the classic “ideal” box does not fit all consumers and should be replaced.

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Journal of Food Science 88(5), 2168–2177 · doi:10.1111/1750-3841.16531

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Liang et al., 2021 – Immersion at equilibrium. Derives a desorption model for full immersion brewing and tests it at brew ratios up to 25. Yield settles at about 21% over a wide range of ratios, TDS follows the ratio, and oven-dried grounds underestimate the yield because they hold extracted liquid.

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Scientific Reports 11, 6904 · doi:10.1038/s41598-021-85787-1

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Gloess et al., 2013 – Nine brew methods. Compares espresso, lungo, capsule, moka pot, French press, Karlsbad pot and filter coffee by total solids, instrumental analysis and sensory panel. The moka pot gave the highest yield, and even filter coffee reached 19%.

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

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Smrke et al., 2024 – Fines in espresso. Follows extraction over the course of espresso shots of 20 g to 40 g and spikes coffee with fines. Shots of under 10–15 s already reached more than 80% of the maximum yield, and fines acted mainly on bed permeability rather than on extraction efficiency.

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

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