Water Composition In Coffee – Groundwater with an average residence duration of months to years has a much lower mineral concentration than tap water from a lake or re-infiltrated from a river.
Furthermore, carbonate-bearing bedrock has a higher mineral richness than silicate-bearing bedrock. For example, the mineral concentration of groundwater in Switzerland’s Central Plateau (fine sediments rich in carbonates) is approximately five times higher than in the central and southern Alps (crystalline rock dissolves more slowly and contains little carbonates).
Now that we have introduced some basic properties of water content, the information we can address two central concepts linking water to coffee that will guide our discussions alkalinity and total hardness.
Alkalinity represents the capacity of water to buffer acids. The amount of acid that has to be added to a water sample, or even to a coffee brew, until a specific pH is reached is a measure of its alkalinity.
If, for example, an acid is added to a coffee brew, its pH will decrease. The more acid must be added to reach a specific pH, the higher the alkalinity.
Alkalinity should not be confused with a solution that has an alkaline pH, which simply means that its pH is higher than 7 (at 25C).
Alkalinity reflects the capacity of water or coffee to resist a change in pH when acids are added, irrespective of their actual pH value. For freshwater, alkalinity can be calculated by the following equation:
For water with a pH below 8.3, alkalinity can be accurately approximated from the HCO3 content [Standard Methods for the Examination of Water and Wastewater (SMWW), 2012].
This is because all other components (CO32, OH, and Hþ) are present in concentrations several orders of magnitude lower than HCO 3.
Above pH 8.3, a substantial contribution from the carbonate ion CO32 must also be considered, though this only occurs in regions with hard water (more than 370 ppm CaCO3 of alkalinity).
Although rare, it occurs in some regions characterized by dominant carbonate bedrock. For example, in the canton of Zurich region, at least 10% of all tap water has alkalinity above 370 ppm CaCO3 of alkalinity.
Water’s Hardness Composition
The term “hardness” will be used in this chapter to refer to “total hardness,” which is defined as the sum of quantities or equivalent concentrations of calcium and magnesium according to worldwide industrial regulations (SMWW; DIN 38409-6, 1986; ASTM D-1126, 2002; EPA Method, 130.2, 1982). (see Section 3.3 for calculation).
On the other hand, it is defined as the most significant scale that can form for a particular water composition and is calculated by the lowest standard hard minerals’ minimum total hardness and alkalinity.
Total hardness and alkalinity are both reduced in equal amounts during scale formation. The total hardness of most natural water sources is higher than the alkalinity, as seen in Fig.
The total hardness is lowered without changing the alkalinity when a softener removes calcium or magnesium and replaces it with sodium or potassium (see Fig. 16.2B). In this situation, total hardness is lower than alkalinity, and carbonate hardness is the same as total hardness.
When measuring the hardness of coffee espresso brewing water, it’s essential to understand the difference between amount concentrations, such as mol/L (where 1 mol equals 6.4 1023 atoms, ions, or molecules), and mass concentrations, such as mg/L on bottled water.
While quantity concentration refers to the number of entities present in a specific volume of water, mass concentration relates to the weight of compounds present in the same volume of water.
Table 16.1 provides an overview of the conversion factors for the most commonly used units in water analysis; the values have been calculated based on the IUPAC Periodic Table of the Elements (2013) and are also in agreement with Hem (1985) and the DIN norm for water hardness (1986).
Please note that the standard unit used by the Specialty Coffee Association of America (SCAA), “ppm CaCO3” (or “mg/L CaCO3”), is often misleadingly abbreviated as ppm or mg/L for both total hardness and alkalinity (see Section 4.3 on water standards), since “straight” mass concentrations (as labeled on water bottles) does not correspond to the proper proportions of calcium, magnesium, and hydrogen carbonate.
Scale Formation and Corrosion
Scale residues are primarily of calcium carbonate (CaCO3) and, at high pH (>10), magnesium hydroxide (Mg(OH)2). Water boilers in homes and industrial equipment can get encrusted with scale residues.
The latter happens in steam boilers, especially when the water is sodium-softened. The solubility of calcium carbonate at the given temperature and pH conditions determines the pace of this process.
The most significant technical issues about scale formation when utilizing hard water are a reduction in heating system efficiency (when the coating of scale acts as an insulator) and valve and flow restrictor blockage (usually called killers in coffee machines).
On the other hand, a water filter pitcher that is very low in alkalinity can quickly become acidic (since the insufficient acid buffer is present), a flavor that can cause metal parts’ corrosion
To increase longevity and hence reduce maintenance costs for coffee espresso machine grinders, several countries have issued recommendations to minimize the costs of scale formation (high hardness and alkalinity values) and corrosion (generally low mineral content and low alkalinity in particular).
In Switzerland, only a recommendation about hardness specifies the optimal hardness as 12e15fH (SVGW, 2008). In other countries, optimal ranges for alkalinity are provided that are typically between 5 and 6fH (Navarini and Rivetti, 2010).
As an additional measure, coffee machine companies recommend regular descaling using acid dissolved in water (preferably with little taste) and offer commercial solutions research.