Inspired by this summer's release of the SCAE water chart report (Full title: The SCAE Water Chart: Measure Aim Treat
, by Marco Wellinger, Samo Smrke and Chahan Yeretzian, Zurich University of Applied Sciences), I decided to create a graph similar to theirs that depicts their recommended core zone for hardness/alkalinity along with previous work, including the 2015 Water for Coffee
book (Colonna-Dashwood and Hendon), the 2011 SCAA Water Quality Handbook
(Beeman Songer, and Lingle), the 2002 (alt.coffee) Jim Schulman's Insanely Long Water FAQ
, plus a few points of interest from bottled or formulated water that have been discussed here on the home-barista forum. (Note: I did run my graph by Marco Wellinger, as well as Maxwell Colonna-Dashwood to make sure they were OK with posting my representation of their data here.)
There's nothing new here - it's a simple representation of frequently discussed water specs in one hardness:alkalinity graph. It may be interesting, perhaps educational for analytic types wanting to understand this stuff, and hopefully useful in pointing out the wide variety of waters that have been found to work well for coffee brewing, as well as the areas of agreement across many different recommendations.
I should point out that while a hardness:alkalinity analysis is more sophisticated than, say, a TDS meter measurement, it may still sometimes be an oversimplification. Other ions, especially chloride and to a lesser degree sulfate can be very important in deciding if the water might cause corrosion problems. Also, the proportion of magnesium to calcium may make a small difference in taste and a big difference in scale deposits.
For a definition of the terms hardness and alkalinity, and units and conversions for quantifying those measures see my follow-up post.
Explanation of the shaded areas, zones, and points on the graph are provided in the text below the graph image. Some key references are included at the end of this post.
Pink/Green Shaded Areas
The area lightly shaded in green should be relatively scale free. Within that shaded area it should deposit no scale at temps of 120C or below (appx. 1 bar gauge pressure at sea level).
The area lightly shaded in pink might be excessively scale-prone. At the border of that shaded area, a boiler at 95C might drop about 12 mg of scale per liter of throughput, and at 130C it might drop about 30 mg per liter.
The white zone between the two shaded zones is an area where the water may or may not deposit scale, depending primarily on the boiler temperature.
Both of those shaded areas are based on the scaling calculations from Jim Schulman's modified Langelier/Puckorius equation as described in his FAQ. If your water has significant magnesium (which means relatively less calcium hardness) the borders of these zones would shift upward on the graph.
The best source for understanding and calculating scale deposition rates is Jim Schulman's Insanely Long Water FAQ (see reference section for links).
The hardness=alkalinity Line
In natural waters, for points above this line, "temporary hardness" = total alkalinity. And for points below this line "temporary hardness" = total hardness. Temporary hardness here being the calcium and magnesium that is associated with carbonates and which might precipitate (i. e., form scale) when the water is heated. For points above the line the remainder of the total hardness is "permanent hardness" which is due to soluble calcium or magnesium salts of sulfate, chloride, or possibly a small amount of nitrate.
The hardness = 1.8 * alkalinity Line
This line represents a non-carbonate hardness to alkalinity ratio of 0.8. If the water were composed entirely of calcium and magnesium salts, and if the only anions of those salts were carbonates, chlorides, and sulfates, then this line would correspond to a Larson-Skold index of 0.8. (http://corrosion-doctors.org/Cooling-Wa ... -Skold.htm
) The Larson-Skold index is sometimes used as an indicator of corrosivity, with values in excess of 0.8 being where you might have corrosion concerns with mild steel in water. The SCAE core zone's top border follows this line as a way to keep their recommendation away from potentially corrosive water. Note - this line looks slightly different from the dashed line in fig 6 of the SCAE doc. I think this one is correct (fig 6 of the pdf was evidently distorted a bit in final layout. See SCAE Water Chart is available online
The C-D & H "Roast Correctable" Zone
The area between these two lines is within a zone discussed in the 2015 Colonna-Dashwood and Hendon Water for Coffee book, chapter 12. It illustrates how a roaster might modify roast parameters to produce a coffee that tastes good when brewed with a local water that is far outside the usual ideal brewing windows, and this roasted coffee might taste better with the water under which it was developed than it would with 'ideal' water.
The C-D & H Ideal zone (appx)
This is also from the 2015 Colonna-Dashwood and Hendon Water for Coffee book, Chapter 10. This zone is their "Ideal brew zone." In their book they also present a larger, and slightly differently shaped "acceptable brew zone" (not shown here) and discuss how they arrived at the borders of those shapes based on a combination of theory and experiment. It's important to note that their recommendation zones are all about water for coffee, as opposed to water for espresso machines.
For those of you who are looking at the Water for Coffee book, you probably noticed that my graph has the axes are labeled "hardness as CaCO₃" and "alkalinity as CaCO₃". In the book, the axes are labelled "General Hardness (GH, [Ca²⁺] + [Mg⁺⁺] in ppm)" and "Carbonate Hardness (KH, [HCO₃⁻] in ppm)". Those labels have caused a little confusion as to whether the units were meant to be measures of ion concentration, or of GH and KH as CaCO3 equivalents. (See "Water For Coffee" book discussion thread for more detailed discussion of this.) I'm confident this graph correctly represents their zone, and did run it by Maxwell before posting it. It's also the same as Marco Wellinger's representation of their zone in the SCAE water chart.
The SCAA "Superior Brew" and SCAA "Adequate Brew" zones and the SCAA target
The "superior" and "adequate" brew zones are both from the 2011 SCAA Water Quality Handbook. For the superior zone, the recommendation for alkalinity is "at or near 40," so the width of that zone on this graph is my interpretation of what values "at or near 40" might be. Note that there is also an online SCAA table for an "acceptable brew zone" that is slightly different from the 2011 "adequate" zone from the handbook. Both recommendations can be found in the table below:
The SCAA guidelines specify a calcium hardness rather than total hardness, so if your water has significant magnesium you would shift all these SCAA zones upward in my graph.
The SCAE "Core Zone"
This is an eyeballed representation from the SCAE water chart report by Marco Wellinger et al., specifically from Figure 8: SCAE core zone as recommendation for espresso machines and hot water boilers.
It's interesting to note the borders of this zone. The left border is roughly where the alkalinity might be getting too low to prevent corrosion due to acidity, and the upper border follows a possible Larson-Skold index, where above the line you might expect corrosion due to chloride and sulfates not balanced by bicarbonate. The right border is where you might be getting into high scale deposit problems, and the lower border follows recommendations from Colonna-Dashwood & Hendon's Water for Coffee book for optimal taste.
(Initially, this report was freely available*, and is a highly recommended read. See the references section below.)
*note: As of Dec 2016 that report was no longer openly available to non SCAE members.
Volvic is a frequently recommended bottled water on this forum. As natural waters go, it is somewhat high in magnesium - the calcium hardness is only 30 mg/l and the magnesium hardness is 33 mg/L (63 mg/l total hardness). So it should not cause scale problems even though it's pretty far away from the green 'scale free' zone. The other potentially objectionable minerals in Volvic are reasonably low. Chloride, at 14 mg/l in this report is just within the Synesso espresso machine max recommendation, which is probably the most stringent out there. This Volvic data is based on a 2012 analysis and report: http://www.volvic-na.com/pdf/Water-Qual ... t-2012.pdf
A formulated mix proposed and used by 5 Senses Coffee in Australia - https://s3-ap-southeast-2.amazonaws.com ... recipe.pdf
, and discussed here on HB: 70/30 Water
. This recipe uses 70 ppm sodium bicarbonate and 30 ppm Epsom salt, hence the "70/30" moniker, and comes out to a hardness:alkalinity of about 25:42. There is no calcium hardness in this water and it should not scale. There is no chloride, and the sulfate is relatively low - the Larson-Skold comes out to about 0.6 so there shouldn't be a corrosion concern with this water.
A popular mix by folks on Barista Hustle forums, including Matt Perger. Discussed on HB here: Matt Perger's water recipe for coffee - Is it ok/safe for espresso machines? What do you think?
Most of the people making this formulation are using a mix of Epsom salt plus sodium and/or potassium bicarbonate. This particular mix is all magnesium hardness and no calcium hardness, so should probably not scale despite the high hardness. Although it has a healthy alkalinity, it might be a corrosion concern because of the relatively high sulfate/bicarbonate ratio (the Larson-Skold index on this water is 2.0).
Jim Schulman FAQ
This point is at 90 mg/l hardness and 50 mg/l alkalinity, and is mentioned in a couple places in the Jim Schulman FAQ. It's an example of water that should cause neither corrosion nor excessive scale problems as well as produce a tasty espresso.
Is often recommended as a reliably soft non-scaling water, and is one example of a purified drinking water that has a small amount of minerals added to RO or distilled water.
Both of the Scott Rao books listed in the references below contain this recommendation. His full spec is:
TDS 120-130 mg/L
Hardness 70-80 ppm
Alkalinity 50 ppm
The water for the World Brewers Cup and Barista Championship has generally followed the SCAA target. For Dublin, 2016 they changed to a slightly softer water than in previous WBC events.
See http://www.worldbrewerscup.org/wp-conte ... edited.pdf
Hard (~6 gpg) water after conventional softening
This is just one example of a conventionally softened (strong acid cation exchange) water, as you typically find in home water softeners and in many commercial coffee shops in areas of hard water.
1 mmol/l KHCO3 (rpavlis)
This is a popular water among home barista members, as used by chemistry professor Robert Pavlis (rpavlis on HB). Is purified water with 100 mg/L of potassium bicarbonate added. Is easy to make, will not scale, and has enough alkalinity to avoid corrosion in vintage equipment. Despite having no hardness at all, lots of folks find that it makes perfectly tasty espresso. Dr. Pavlis would use this at as little as half strength (25 mg/L alkalinity) when pulling darker roasts.
Schulman, J., Jim Schulman's Insanely Long Water FAQ
, alt.coffee posting, 2002, http://web.archive.org/web/200805260723 ... erfaq.html
and http://users.rcn.com/erics/Water%20Qual ... %20FAQ.pdf
Colonna-Dashwood, M & Hendon, C. H., Water For Coffee
, Self-Published, 2015, waterforcoffeebook.com (Edited: The book is out of print, and that domain name appears to have been stolen)
Scott Rao, The Professional Barista's Handbook
, Fourth Edition, Independent Publisher, 2011, http://www.theprofessionalbaristashandbook.com
Scott Rao, Espresso Extraction: Measurement and Mastery
, Self-Published 2013, https://www.amazon.com/Espresso-Extract ... B00F2VCTP6
Specialty Coffee Association of America, SCAA Standard | Water for Brewing Specialty Coffee,
November 2009, online PDF: http://www.scaa.org/PDF/resources/water-standards.pdf
D. Beeman, P. Songer, T. Lingle, Specialty Coffee Association of America, The Water Quality Handbook
, Second Edition SCAA 2011, https://store.scaa.org/collections/bari ... nt-version
M. Wellinger, S. Smrke and C. Yeretzian, The SCAE Water Chart: Measure Aim Treat
, (Specialty Coffee Association of Europe, 2016), http://scae.com/images/pdfs/SCAE-water-chart-report.pdf
(Initially was freely accessible via the preceding URL, as of Dec 2016, appears to be available to SCAE members only: http://scae.com/tools-and-resources/res ... ater-chart
Edit addition Note: If you are not an SCAE member, you can get much of the same information from Chapter 16 of the Craft and Science of Coffee book, available for free download here: https://www.researchgate.net/publicatio ... _Treatment