Water for coffee extraction

Water for coffee extraction:

Composition, recommendations and treatments

Dr. Marco Wellinger Zurich University of Applied Sciences ICBC - LSFM W?denswil, Switzerland weli@zhaw.ch

Marco Wellinger

1

Take-home messages

? Key parameter which characterize potable water for coffee extraction:

? Odor free ? Total hardness ? Acid buffer capacity ? Traditional hardness units (ppm CaCO3, ?d, ?f) provide an easy and accurate way to assess a water's suitability for use in coffee extraction

? SCAA/SCAE and the book "Water for Coffee" do agree largely on their recommendations: large variation allowed for total hardness but a small variation for the buffer capacity

? All water treatments can be compared using a simple chart of total hardness and buffer capacity

MaMrcaorcWoelWlinegellringer

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How water acquires its mineral content

? Rain water takes up carbon dioxide and carbonic acid is formed: CO2 + H2O -> H2CO3 => water becomes acidic pH < 5.7

? Acidic rain water that comes into contact with carbonate rock (MgCO3/CaCO3) dissolves part of it and acquires magnesium, calcium and hydrogen carbonate ions (HCO3-)

? In case of silicate rock (SiO4 compounds) the water stays very soft ? In general groundwater is harder than water in rivers and lakes

because it has been in contact with minerals for a longer period

MaMrcaorcWoelWlinegellringer

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Water composition illustrated

Ca2+ Mg2+

HCO -

3

CO32-

Na+ K+ Cl- NO3- SO42-

Silicates, organic compunds

Why are the two bars of positive ions and negative ions equally big?

Because charge neutrality is always fulfilled! Number of positive charges = Number of negative charges

Calculation is based on the number of molecules and their charge and not on their mass.

Marco Wellinger

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Mole: the chemical dozen

Mole is a scaling factor transforming the mass of molecules from atomic units to grams.

Mole is useful for counting the number of molecules that are present in a water sample or a brewed coffee.

By multipling the molar concentrations of all ions with their charge we can calculate the fundamental balance that has to be fulfilled for every water sample (charge neutrality).

Marco Wellinger

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Mass versus molar versus equivalent concentrations

Example for mass concentrations compared to molar concentrations and charge equivalent concentrations.

Zurich tap water composition ? average for 2014

/L /L /L

Source:

Marco Wellinger

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Hardness and alkalinity

Total hardness: The sum of calcium and magnesium in equivalent concentrations (or molar concentrations). In rare cases other ions can contribute to hardness, for example strontium.

Alkalinity = Acid buffer capacity: The amount of acid that has to be added to a water sample to decrease pH to 4.3. Therefore it is neutralizing/buffering the effect of adding acid to a water.

Marco Wellinger

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Hardness and alkalinity

Total hardness

Carbonate hardness Non-carbonate hardness

Ca2+ Mg2+

Na+ K+

HCO3-

Cl- NO3- SO42-

Alkalinity

Marco Wellinger

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