What the free SCAA brewing-water tables actually cite

The familiar 150/68/40 triad — 150 mg/L total dissolved solids, 68 mg/L calcium hardness, and 40 mg/L total alkalinity — appears in free specialty-coffee standards as brewing-water targets. This article asks a narrower question than whether those numbers are good brewing advice. It asks what those free documents cite in support of them, and whether the historical water-flavor papers later cited by Hendon et al. 2014 supply the missing derivation.

The answer is short. Both free tables present the figures as committee-determined target optima. Both point readers to a Water Quality Handbook for testing equipment and protocols. Neither free document supplies a panel study, committee minutes, bibliography, or derivation for the three numbers. Lockhart, Tucker, and Merritt 1955, which Hendon cites as prior experimental work on water impurities and coffee flavor, does not state or derive 150/68/40 either. The paid handbook sold for testing detail has not been read for this article, so the trail stops there rather than in a claim that no derivation exists anywhere.

What the 2009 SCAA standard states

The document is titled SCAA Standard | Water for Brewing Specialty Coffee, revised 21 November 2009, identified as WATER_STANDARD VERSION 21NOV2009A, Cover + 1. Its purpose sentence says the Statistics & Standards Committee of the Specialty Coffee Association of America “has determined” the standards for water used to brew specialty coffee.

For the three numbers that circulate, the table is exact:

The document also defines what “Target” means in its own words: the most desirable point in the Acceptable Range; falling within the range meets the standard; the target is “the optimum measurement” of each characteristic to strive for. That is a committee recommendation about optima, not a reproduced experimental result.

Footnotes on the same page explain measurement framing that is easy to confuse with derivation. Odor and color determinations are sensory. TDS is “measured based on a 4-4-2 conversion.” Those notes tell a reader how the characteristic is to be judged or converted. They do not explain why 150, 68, or 40 were chosen.

Target, range, measurement, and derivation

It helps to keep four kinds of claim apart, because field writing often collapses them.

Target. The single preferred point the committee names — 150, 68, 40.

Acceptable range. The band that still meets the standard — for alkalinity, phrased as “at or near 40 mg/L” rather than a numeric interval.

Measurement protocol. How to obtain the reading used against the table. The free standard’s only external pointer is exactly that: “For details of testing equipment & protocols, please see the SCAA Water Quality Handbook.”

Scientific derivation. Why those particular figures rather than others — panel data, calculation, cited prior study, or other supporting record. The free one-page standard does not supply one. It contains no bibliography, no sensory-panel write-up, no committee minutes, and no derivation of 150/68/40.

So a reader can accept the free document as a published target table without treating the handbook citation as evidence for how the targets were chosen. The handbook is invoked for how to test, not as a displayed citation for why the numbers exist.

The 2018 compilation repeats the table, not the missing support

In 2018 the Specialty Coffee Association issued Coffee Standards, a compilation. Page 4 defines an SCA standard generally as a Standards Committee recommendation that is “based upon scientific testing.” Section 4.1 then reprints the brewing-water table with the same 150/68/40 targets and the same acceptable ranges, again attributes the determination to the Statistics & Standards Committee, and again points to the SCA Water Quality Handbook for “testing equipment & protocols.”

What section 4.1 does not add is a citation or derivation specific to this water table. The compilation’s general statement that SCA standards rest on scientific testing is not the same thing as showing the scientific testing for these three figures. Repeating the table under a later imprint does not close the provenance gap in the free record.

Where the free trail stops

Two further records define the limit of the public trail without turning that limit into a claim that nothing else exists.

The Specialty Coffee Association standards index cited in the References lists published standards for coffee value assessment, professional competencies, and several member-access certification standards. It does not list a free Water for Brewing Specialty Coffee PDF among those published standards. That is a statement about that cited index page, not a claim of permanent absence or of supersession by another numbered document.

Separately, the SCA digital store lists The 2018 SCA Water Quality Handbook (ISBN 978-0-9995807-3-8) for sale at $45. That handbook has not been purchased or read for this article. Its contents are therefore unknown here. It may contain derivation, history, panel work, or only the testing protocols the free standards already promise. Until it is read, the honest statement is the limited one: the free standard does not show its derivation, and the paid handbook remains unread.

Hendon 2014 and the historical papers it cites

Hendon, Colonna-Dashwood, and Colonna-Dashwood, Journal of Agricultural and Food Chemistry, 2014, does not fill the free-standard gap. The paper discusses Specialty Coffee Association of Europe (SCAE) guidance, not the 2009 SCAA table. As Hendon reports it, SCAE suggests a vague upper limit around 300 ppm TDS; Hendon calls that guidance vague. The method is density-functional-theory comparison of relative cation binding to selected coffee compounds, not a sensory panel on 150/68/40 water. The authors state that macroscopic flavor effects of the magnesium-versus-calcium difference they compute “would be better probed experimentally.”

That paper can be useful for what it is: a computational argument about cation binding. It neither derives nor retrospectively explains SCAA’s 150, 68, and 40 figures. What it does do, for this provenance check, is name two earlier experimental studies as the detailed prior work on water impurities and coffee flavor: Lockhart and co-workers, and Pangborn and co-workers.

Lockhart, Tucker, and Merritt 1955

Lockhart et al., “The Effect of Water Impurities on the Flavor of Brewed Coffee,” Journal of Food Science 20 (1955), 598–605, states its object as determining what effects impurities normally present in water might induce in brewed coffee. The method is randomized triangle testing with panels of eighteen or more experienced food-quality judges: first single-ion solutions in distilled water, then coffee prepared at threshold and at stepwise higher concentrations. That is a threshold and detectability study of individual inorganic components, not a hardness/alkalinity/TDS target-matrix experiment.

Its paper conclusion is correspondingly narrow: except for local conditions and isolated cases, the inorganic components of water supplies studied should not affect the taste of brewed coffee. The paper does not state, recommend, or derive the SCAA targets of 150 mg/L TDS, 68 mg/L calcium hardness, or 40 mg/L total alkalinity. Individual threshold and detectability concentrations in its tables are not modern brewing optima, and this article does not promote them as such. Lockhart therefore does not itself supply the free standard’s missing derivation of 150/68/40.

Pangborn, Trabue, and Little 1971

Hendon’s second historical citation is Pangborn, Trabue, and Little, Journal of Food Science 36 (1971), 355–362. The bibliographic record and abstract are verified; the full text has not been legally obtained or read for this article. Body-level conclusions are therefore out of scope.

What the abstract itself displays is limited and usable: coffee, tea, and flavored soft drinks prepared from eight minerals each at 750 ppm, plus coffee and tea brewed with six natural drinking waters ranging from 42–1,725 ppm total dissolved solids. That abstract does not display the SCAA 150/68/40 optima. Until the full paper is read, nothing further from Pangborn is claimed here.

Bounded conclusion

In the free specialty-coffee standards record examined here, 150 mg/L TDS, 68 mg/L calcium hardness, and 40 mg/L total alkalinity appear as Statistics & Standards Committee target optima. Those free documents distinguish targets from acceptable ranges and from testing protocols, but they do not show how the three figures were derived. Lockhart 1955, the historical study Hendon cites for water-impurity flavor work, does not derive them either. Pangborn 1971 remains unread beyond its abstract, which likewise does not display the triad. The 2018 Water Quality Handbook remains the precise unread stopping point on the standards side.

What this check does not establish

It does not establish that the targets are wrong, arbitrary, or unsupported in every document that exists. The unread handbook is an accepted limitation, not empty evidence.

It does not establish supersession of the 2009/2018 free tables by a later free standard. The cited public standards index simply does not list a free Water for Brewing PDF among its published standards.

It does not independently establish the complete or current SCAE water guidance. It establishes only what Hendon reported about SCAE, and it does not merge that report with the SCAA table.

It does not recommend a water recipe, magnesium preference, or home-mineralisation target. For SCA 310’s home-brewer test-water summary versus the free brewing-water table, see that reconciliation.