What Is the Study of Coffee Called When Water Chemistry Is Involved?
Water makes up more than 98 percent of brewed coffee, which is why its mineral content matters so much. In 2014, Christopher Hendon and Maxwell Colonna-Dashwood published research on how sodium, calcium, and magnesium ions affect the extraction of flavor compounds, work that later became the book Water for Coffee.
Their framework weighs general hardness, driven largely by calcium and magnesium, against carbonate hardness. The two sit in a dynamic balance, and the authors proposed roasting to match the water rather than treating water as a fixed input. RO water, tap water, mineral water, and hard or soft water each pull different compounds from the same grounds.
Water makes up over 98% of brewed coffee, yet it has long been overlooked. Different types of water—RO water, tap water, mineral water, soft water, hard water—have a huge impact on extraction flavor. In 2014, Christopher Hendon and Maxwell Colonna-Dashwood published research revealing how sodium, calcium, and magnesium ions influence the extraction efficiency of flavor compounds, and subsequently published the book "Water for Coffee," which systematically discusses the dynamic balance between GH (General Hardness) and KH (Carbonate Hardness), and proposes the reverse thinking of "Roasting to water." This article will review these key findings to help coffee enthusiasts understand how water quality shapes the flavor in the cup, and include relevant recommendations from the Front Street brand.
The Water Quality Research That Shook the Coffee World
Among the many factors in brewing coffee, the importance of water is often underestimated. In a finished cup of coffee (except espresso), water accounts for over 98%, making it absolutely dominant. However, the water sources used daily vary greatly: RO purified water, tap water, mineral water, hard water, soft water... the variety is dazzling and bewildering.
Isn't water all the same? Why divide it into so many types?
How do different water qualities affect coffee extraction?
Isn't it good to brew coffee with purified water?
Is it a good thing for water to contain minerals?
What is the scientific basis behind it?
In recent years, the coffee community's attention to "water" has continued to heat up. Previously, the SCAA's publication "Water Quality" was considered the most complete classic discussion in this field, but most of the references in the book regarding the relationship between minerals and brewing came from publications by the Coffee Brewing Center in the 1960s and 1970s, with few breakthrough insights since. It was not until the past two years that a duo brought new discoveries about water quality through scientific research, shaking the entire coffee world. In this column, the author will introduce them to you.
In 2014, Christopher Hendon, a doctoral student at the Centre for Sustainable Chemical Technologies at the University of Bath in the UK, and local café owner Maxwell Colonna-Dashwood published a paper on cations and coffee extraction in the Journal of Agricultural and Food Chemistry, titled "The Role of Dissolved Cations in Coffee Extraction," thus opening the prelude to exploring the ideal water for brewing.
(Maxwell and Christopher / Image source: Internet)
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The Impact of Ions in Water on the Extraction of Flavor Compounds
The paper selected three common cations in water: sodium ions, calcium ions, and magnesium ions, and analyzed their effects on the extraction of coffee flavor compounds. The authors first selected seven chemical substances to represent coffee flavors: lactic acid, malic acid, citric acid, quinic acid, chlorogenic acid, caffeine, and eugenol. Among them, lactic acid and malic acid represent sourness, citric acid represents sweetness, quinic acid and chlorogenic acid represent pungency and unpalatable flavors, and eugenol (also commonly found in coffee whiskey and red wine) represents pleasant woody flavors. Then, thermodynamic methods were used to calculate the relative binding energy of sodium, calcium, and magnesium ions, as well as water, with these seven components, as extraction indicators.
The study found that the relative binding energy of sodium ions with the selected coffee components is comparable to that of water, meaning the presence of sodium ions does not interfere with water's binding to these substances; indeed, sodium ions bind even more weakly than water to caffeine and eugenol. Therefore, the authors believe that the commonly available sodium ion exchange calcium ion resin on the market functions at most to reduce scale, with little help for flavor extraction; moreover, water rich in sodium ions after exchange may even affect the extraction of certain flavors (such as caffeine and eugenol). As for divalent metal ions (calcium and magnesium ions), their binding ability with the selected flavor components is superior to sodium ions and also stronger than water. This indicates that when these two minerals are present in water, flavor components tend to bind with them, thereby enhancing extraction efficiency.
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Analysis of Ion Characteristics: Pros and Cons
Further comparison found that magnesium ions have slightly stronger binding ability than calcium ions. It is worth noting that these divalent cations enhance extraction comprehensively, including unpleasant flavors (such as chlorogenic acid and quinic acid selected in the paper), as well as substances with potential pharmacological effects (such as chlorogenic acid having antioxidant effects, and caffeine stimulating the nervous and gastrointestinal systems), so health factors must also be considered when choosing, requiring some attention.
Although both calcium and magnesium have good extraction capabilities, excessive calcium ions in water easily combine with bicarbonate to form scale, affecting hot water equipment, so using magnesium ions seems to be a better choice. The paper also mentions that when brewing instant coffee, to achieve maximum dissolution and extraction, water containing magnesium ions is ideal; if brewing light-roasted coffee, calcium and magnesium ions have comparable abilities. After the paper was published, it immediately sparked curiosity about magnesium ions, and people began looking for ways to add magnesium ions to water, leading some businesses to introduce magnesium ion filter cartridges or exchange resins for enthusiasts to try.
Rather Than Changing Water Quality, Adjust Roasting Methods to Correct Extraction
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In-Depth Analysis of Coffee and Water
Following the publication of their 2014 paper, the two pressed their advantage and published a book dedicated to exploring coffee and water at the end of 2015, titled "Water for Coffee." Based on their previous research, the book also explains in detail the buffer system not discussed in the paper, with substantial and complete content, providing an excellent reference guide for the coffee industry. The following is a brief outline of the content.
The book is divided into three major parts. The first part is popular science knowledge. The authors start from the birth of the universe and the periodic table, introducing commonly used chemical terms and scientific units for use in subsequent discussions. Then they discuss the relationship between water's liquid, vapor, and solid states and temperature and pressure, the four laws of thermodynamics, and other physical properties of water; as well as the chemical composition and structure of water, what polarity and non-polarity are, the generation of hydrogen bonds, and the relationship between water and polar molecules and non-polar molecules; and viewing substance dissolution from a thermodynamic perspective, telling readers the scientific theoretical basis for substances dissolving in water. Then they discuss the dissociation constant and pH value of water, the definitions of acids and bases, conjugate bases and buffer solutions, and introduce carbonate hardness (KH) of water, as well as the concept of general hardness (GH).
From the structure, the authors seem to take the four indicators in the current SCAA-recommended "water for brewing standard": TDS (Total Dissolved Solids), pH value, Calcium Hardness, and total alkalinity as the starting point, ambitiously intending to provide a complete introduction to water and propose their own version (such as revising Calcium Hardness to General Hardness, and Total alkalinity to Karbonate Hardness), laying the theoretical groundwork for subsequent content.
Some of my friends, upon flipping to the first part, were discouraged by the overly chemical content. Actually, we all encountered this chemistry during our education; perhaps it has been too long, but please don't give up too early, because the best is yet to come!
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Exploration of Water Filtration, Hardness, and pH
The second part begins by introducing several current methods for measuring minerals in water, such as the commonly used "titration method," TDS measurement, and laboratory-grade atomic absorption spectroscopy (AA) and inductively coupled plasma mass spectrometry (ICPMS). Then it discusses common water filtration methods: from simple activated carbon filter cartridges that remove organic molecules such as pesticides, to the principles of cation exchange resins and their impact on water quality, as well as the principles of reverse osmosis. It is worth mentioning that abroad, even when using reverse osmosis, people rarely drink the purified water directly; they usually backfill some of the high-concentration ion wastewater into the purified water to supplement minerals. In Taiwan, however, purified water is mostly passed through maifan stone filter cartridges to increase mineral content, which is slightly different.
Next, the third part becomes interesting. First is the practical section, where the authors use magnesium and calcium ions as examples to teach everyone how to prepare water with different general hardness (GH), carbonate hardness (KH), and adjusted pH values, and even tell everyone how to purchase the needed chemicals online and their prices. If you are interested in personally trying how different ion types and concentrations in water affect the flavor of brewed coffee, it is recommended to refer to the recommended concentrations in the SCAA "water for brewing standard" to prepare, as a starting point for exploration.
Next, the authors discuss what they consider the three factors in water that affect extraction: the relationship between calcium ions, magnesium ions, and the carbonate buffer system. Interestingly, the author found that they seem to have realized that publishing that magnesium ions have better binding ability might mislead readers, since calcium ions are also quite capable. So the authors added that what they want to emphasize more is the impact of water's composition on extraction, rather than emphasizing a single ion. They return to the concept of general hardness GH (viewing magnesium and calcium ions together), since finding a water source containing only abundant magnesium ions in nature is as difficult as finding deionized water. Furthermore, they had 14 people blind-test coffee brewed with calcium ion or magnesium ion water, and the difference was negligible.
In addition, regarding the carbonate buffer system, there are currently many synonyms, such as Alkalinity, Karbonate (carbonate), Hardness (carbonate hardness), temporary Hardness, etc. The authors strongly recommend not using "alkalinity" because carbonate has buffering capacity, and "alkalinity" can be misunderstood as "alkaline." The carbonate system is another main axis emphasized by the authors, because carbonate (KH) has buffering capacity, which can not only stabilize the pH value of water but also partially neutralize and buffer the acidity of coffee during brewing, so the KH content also influences cup quality performance.
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What Is the Most Suitable Water for Brewing Coffee?
The climax of the third part, and what the author considers the most exciting part, is the discussion of the so-called "optimal" water specifications. The authors reiterate that discussion should not focus on a single ion, but rather dynamically consider the ratio of the three factors, thus presenting a brewing flavor chart examining brewed coffee under different KH (carbonate hardness) and GH (general hardness, the sum of calcium and magnesium ions) concentrations.
The Flavor Chart Concept Proposed by Maxwell and Christopher
The role KH plays is buffering the acidity of coffee: too little may bring sharp acidity, too much will neutralize the coffee's acidity, causing a flat acidity, and sometimes even causing precipitation with a chalky texture. GH is the extraction indicator, the ability to dissolve coffee substances; the higher the GH, the heavier the mouthfeel, and vice versa, the emptier. As shown in the figure, between the four extreme flavors produced by different high and low concentrations of GH and KH, there will be an acceptable range, and even within the acceptable range, an ideal zone will emerge.
Finally, the authors propose the concept of "Roasting to water." Their theory is that no single water's mineral composition in the world is suitable for all coffee brewing, because the ion composition in water affects coffee flavor, and water quality conditions differ by region, so the brewed taste differs. Therefore, to achieve ideal flavor, they advocate a reverse-thinking concept: rather than changing water quality, adjust roasting methods to correct extraction. This is a brand-new concept! However, the author's ideal in mind is that one day, our control over water quality will be随心所欲, allowing us to adjust water with different GH and KH ratios to brew coffee from different regions, or even coffee of different roast levels. By then, customers entering a coffee shop will have, in addition to traditional choices, the option of water quality. With such combinations, tasting coffee will become even more interesting.
The above content is compiled by CoffeeHunters, a coffee news website.
