Coffee Sketcher

Total dissolved solids

Properties3
descriptionThe number that tells you how strong a coffee is — how much of the bean actually ended up dissolved in the cup, and how much mineral was in the water to begin with.
tagsconcept, brewing, measurement
aliasesTDS, Brew strength, Total Dissolved Solids

9 min read

Total dissolved solids (TDS)

Total dissolved solids is a measure of how much stuff is dissolved in a liquid. It says how much, never what — a glass of water with 150 milligrams of minerals per litre and a glass with 150 milligrams of sugar per litre have the same TDS and taste nothing alike.

In coffee the term gets used for two completely different liquids, and confusing them is the single most common mix-up around the word:

  • Water TDS — the minerals in the water before it touches coffee: calcium, magnesium, bicarbonate, sodium, chloride, sulfate. Usually quoted in parts per million (ppm), which for water is the same as milligrams per litre.
  • Coffee TDS, also called brew strength — everything the water pulled out of the grounds and is now carrying: acids, sugars, bitter compounds, oils, minerals. Usually quoted as a percentage by weight of the finished drink.

So “50 ppm” and “1.3%” are both TDS figures, and they describe opposite ends of the same brew. A cup at 1.3% TDS is 1.3% dissolved coffee and 98.7% water.

How it gets measured

Two different instruments, because the two liquids need different tricks.

Coffee TDS is read with a refractometer — a small optical device that measures how much a liquid bends light compared with pure water. The more dissolved solids, the more the light bends; the reading is converted into a strength percentage (Roastopedia, accessed 2026-07-23). The working routine, as published by the brewing-equipment maker Fellow (Fellow, accessed 2026-07-23):

  1. Zero the instrument on 3–4 drops of room-temperature distilled water, then wipe the lens.
  2. Stir the coffee — an unstirred brew is layered, and a sample off the top reads differently from one off the bottom — and let it cool to about 100 °F (38 °C) or below.
  3. Put 3–4 drops on the prism, close the lid, wait about 10 seconds for the sample to settle to the instrument’s temperature.
  4. Take the reading 2–3 times.

Water TDS is read with a cheap conductivity meter: dissolved mineral salts conduct electricity, so the meter measures conductivity and estimates the mineral load from it. That works for water and not for coffee — most of what is dissolved in coffee doesn’t carry a current.

Strength versus extraction — the distinction that matters

These two numbers get swapped constantly, and they answer different questions:

  • TDS (strength) — how concentrated the drink in front of you is. Dissolved solids as a share of the liquid.
  • Extraction yield — how much of the dry coffee you dissolved. A share of the ground bean, not of the cup.

You can brew a weak cup that is heavily extracted, or a strong cup that is barely extracted, by changing how much water you use. That relationship is what the arithmetic captures — once a refractometer gives you TDS, extraction yield falls out of it (Roastopedia, accessed 2026-07-23):

Extraction yield (%) = TDS (%) × brew weight (g) ÷ dose (g)

Worked through: 15 g of coffee making 200 g of drink at 1.35% TDS is 1.35 × 200 ÷ 15 = 18% extraction — the bottom of the conventional band, on roughly the 1:13 ratio a competitor might use.

The commonly quoted targets for filter coffee are 1.15–1.35% TDS and 18–22% extraction yield, a pairing that traces back to a Specialty Coffee Association of America standard (11.5–13.5 grams per litre is the same thing as 1.15–1.35%) and its Brewing Control Chart (Roastopedia, accessed 2026-07-23). The 18–22% figure is the more stable half of that pair; the strength band is quoted differently by different people (see below).

What the research actually shows

The clearest peer-reviewed result concerns full-immersion brewing — French press and the like, where the grounds sit in the water rather than having water run through them. A 2021 Scientific Reports paper by Jiexin Liang, Ka Chun Chan and William D. Ristenpart modelled it and found that TDS varies inversely with the brew ratio — more water per gram of coffee, proportionally weaker cup — while extraction yield stayed essentially constant at about 21% regardless of brew ratio, water temperature (80–99 °C) or grind size (Liang, Chan & Ristenpart, Scientific Reports, 2021, accessed 2026-07-23).

Their conclusion, verbatim: “Full immersion brewing offers precise control over the TDS at equilibrium but little control over E, and that practitioners should pay careful attention to their brew ratio as the most important parameter for full-immersion brewing.”

In plain terms: with a French press you are choosing strength, not extraction. That is a genuine constraint on the “dial in your extraction” advice that circulates in brewing circles, and it applies to immersion specifically — pour-over, where water passes through a bed of grounds, is a different mechanism.

Where this shows up on the wiki

  • World Brewers Cup puts a hard ceiling in the rulebook: the brew must measure 2% TDS or less (20,000 ppm). That single number is what keeps the event a filter competition — it stops a competitor serving something at espresso concentration.
  • Nas Jaafar, the 2026 Brewers Cup champion, brewed on water at 50 ppm — very soft, close to a blank canvas, with just enough magnesium and calcium to help pull flavour out.
  • Tetsu Kasuya went further in 2016, competing on water at 0.33 ppm dissolved solids — effectively nothing, so that nothing in the water competed with the coffee.

Those two competition figures sit at or below the bottom of every published brewing-water recommendation, which is worth noticing: the guidance describes what works day to day on a bar, not what wins on a stage.

TDS is also the standard quality-control number in roasteries and cafés — the cheapest way to check that today’s batch matches yesterday’s. It does not replace tasting. It tells you whether two cups differ and by how much; only cupping tells you which one is better.

To verify

The SCA’s brewing-water numbers. Two different ranges circulate for the SCA’s recommended water TDS: 75–250 ppm and approximately 50–175 ppm, both quoted with a target of about 150 ppm. Only the 50–175 figure was confirmed at a source here (Coffeester, accessed 2026-07-23), which cites the SCA generally without naming a document. The same page gives total hardness 17–85 ppm, alkalinity ≈40 ppm bicarbonate, pH 6.5–7.5, sodium below 30 ppm, and chlorine not detectable. The Specialty Coffee Association’s own standards page publishes no numeric water values in the open — they sit inside downloadable standard documents (SCA — Coffee Standards, accessed 2026-07-23). Treat every figure in this callout as a secondary reading of an SCA document nobody in this research chain opened.

To verify

The filter strength band itself. Sources disagree. Roastopedia gives 1.15–1.35% TDS; Fellow gives 1.2–1.5% for pour-over and adds that specialty coffees can reach around 25% extraction (Fellow, accessed 2026-07-23). Both attach the same 18–22% extraction range. The 1.15–1.35% version is presented as a quotation of SCAA standard text, but the original was not read at source and the SCA has been revising its standards, so the current official wording may differ.

To verify

Espresso at 8–12% TDS. This range is cited in barista training material for concentrated brews (barista.tools, cited in the research report, not independently fetched). No official SCA numeric standard prescribing it was located. It is a practitioner rule of thumb, not a published standard.

To verify

The taste descriptions. The tidy sensory ladder — below 1.1% reading as thin and under-extracted, 1.15–1.35% as balanced and complex, above 1.4% as strong and possibly bitter — comes from a single barista-education source (same page as above, not fetched). So does the claim that very low-TDS water over-extracts into something harsh while hard tap water under-extracts into something flat (Itadi Coffee, cited in the research report, not fetched). Both are widely repeated in practice, and both simplify: mineral balance and alkalinity do work here that a single TDS number cannot capture.

Sources

  1. Liang, Chan & Ristenpart — An equilibrium desorption model for the strength and extraction yield of full immersion brewed coffee, Scientific Reports (2021) — accessed 2026-07-23
  2. Specialty Coffee Association — Coffee Standards — accessed 2026-07-23
  3. Roastopedia — Total Dissolved Solids — accessed 2026-07-23
  4. Fellow — The Beginner’s Guide To Total Dissolved Solids And Coffee — accessed 2026-07-23
  5. Coffeester — Water for Coffee: TDS, Hardness, Alkalinity & the SCA Water Standard — accessed 2026-07-23
  6. Hanna Instruments — The Role of TDS in Coffee & the Science Around your Brew — cited in the research report as the source of the SCAA standard quotation; fetched on 2026-07-23 but returned only page navigation, so the quotation was not confirmed at source
  7. barista.tools — TDS in coffee: values, measurement & perfect extraction — cited in the research report, not independently fetched
  8. Itadi Coffee — The Ultimate Guide to Coffee Water: pH, TDS, and Mineral Content — cited in the research report, not independently fetched
  9. All About Coffee — Total Dissolved Solids — cited in the research report, not independently fetched
  10. Handground — An Intuitive Guide To Coffee Solubles, Extraction And TDS — cited in the research report, not independently fetched

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