water for coffee extractionscae.com/images/pdfs/ast-live-2016/water-composition-for-coffee.pdf ·...
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1Marco Wellinger
Dr. Marco WellingerZurich University of Applied SciencesICBC - LSFMWädenswil, [email protected]
Water for coffee extraction: Composition, recommendations and treatments
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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
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3Marco Wellinger 3Marco Wellinger
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
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Water composition illustrated
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.
Mg2+ Ca2+
HCO3-
Na+ K+
Cl- NO3- SO4
2-CO32-
Silicates, organic
compunds
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5Marco Wellinger
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).
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Mass versus molar versus equivalent concentrations/L /L /L
Example for mass concentrations compared to molar concentrations and charge equivalent concentrations.
Zurich tap water composition – average for 2014
Source: https://www.stadt-zuerich.ch/dib/de/index/wasserversorgung/Qualitaetsueberwachung/qualitaetswerte.html
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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 examplestrontium.
Alkalinity = Acid buffer capacity: The amount of acid thathas to be added to a water sample to decrease pH to 4.3. Therefore it is neutralizing/buffering the effect of adding acidto a water.
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Mg2+ Ca2+
HCO3-
Na+ K+
Cl- NO3- SO4
2-
Total hardness
Alkalinity
Carbonate hardness Non-carbonate hardness
Hardness and alkalinity
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9Marco Wellinger
Mg2+ Ca2+
HCO3-
Na+ K+
Cl- NO3- SO4
2-
Total hardness ≈ carbonate hardness Non-carbonate hardness is zero
Alkalinity
«Not hard» carbonate
Hardness and alkalinity
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Examples for water compositions: tap water
Composition of 186 tap water from a small region in Switzerland (Baselland / BL)
baselland.ch
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Composition of some commercial bottled waters
Examples for water compositions: bottled water
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Water treatment – technical and sensory reasons
• Technical reasons for water treatment: – Too high hardness and alkalinity -> Scale deposits
• Decrease in efficiency of heat transfer• Clogging of valves and orifices (gicleur)
especially in the hot water sections– Too low alkalinity -> Corrosion of metal parts (pitting)
• Sensory reasons for water treatment:– Desired degree of buffering (reduction) of the acidity
– Influence on the extraction efficiency:
• Higher total hardness is suspected to increase extraction efficiency
• Increase in wettability (for softer water)
Quelle: www.kaffeenetz.de
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Comparison of existing standards
• Recommended range for optimum/ideal hardness vary strongly
– Lowest suggested optimum is the revised World Brewers Cup at 51 ppm CaCO3
– Highest suggested optimum is from “Water for Coffee” at 175 ppm CaCO3
• Recommended range for alkalinity is much smaller:
– Lowest suggested optimum is at 40 ppm CaCO3
– Highest suggested optimum is at 75 ppm CaCO3 – apply only for total hardness values of 150 -175 ppm CaCO3
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Measurement methods
Determination of hardness and alkalinity by titration:A solution is added drop by drop to a specified amount of water until a color change occurs (for instance from green to red).Available from water treatment suppliers or also in aquarium stores –minimum recommended resolution is 20 ppm CaCO3 (or 1°d).
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Conductivity meter aka «TDS-Meter»
For a known water composition (or more precisely ratio of ions) conductivity measurements can be transformed into a value for total dissolved solids.
TDS measurements as used by the vast majority has an error of typically +/-30% (and in extremes over 50%) and therefore should not be used as a significant parameter:1. The conversion factor depends strongly on the exact composition;
the conversion factor can vary between 0.5 -1.0 for the transformation of electrical conductivity in µS /cm to TDS in mg/L -SCAA for example uses 0.7.
2. Most cheaper models do not measure and correct for the water temperature: Though a 10°C change (e.g. tap temperature to room temperature) adds another 20% of error to the measurement.
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Water treatments
• Methods:
– Filtration: Removal of particles• Activated charcoal to remove off-flavors such as chlorine
– Reverse osmosis: Non-selective removal of all dissolved solids
– Ion exchanger: Exchange of magnesium- and calcium ions by protons, sodium or potassium ions
– Distillation: Evaporation and subsequent condensation of water
– Precipitation
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Impact of water treatments on total hardness and alkalinity
a : Softener: Ca2+ and Mg2+ against potassium (K+) or sodium (Na+) – only affecting hardness and therefore vertically oriented
b : Decarbonizer: Ca2+ and Mg2+ against H+ ‐ oriented diagonally with a slope of 1 (change in alkalinity equals the change in hardness) b* : Combination of mostly b‐type ion exchanger with a small fraction of a‐type ion exchanger
c : Reverse osmosis (RO) – removing ions non‐specifically and producing a scalar/multiple of the initial composition – oriented towards the point of origin (0/0) or away from it
d : Dealkalizer: HCO3‐ against Cl‐ ‐ not yet commercially
available for coffee applications ‐ or addition of a strong acid (e.g. HCl)
e – not shown: Cation exchange of Ca2+ against Mg2+ ‐ does not change either hardness or alkalinity so the water stays at constant values of both
a
b
b*
c
d
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An applied example for espresso extraction
A local roaster in Switzerland had complained that following the
softening of his very hard water (above 300 CaCO3) by a
decarbonizer (b-type ion exchanger) his espresso was always
very foamy (large bubbles that collapse quickly in the crema).
In fact calculations have shown that a reduction in
200 ppm CaCO3 alkalinity will increase dissolved carbon dioxide
by 240 mg/L.
=> For a standard double espresso recipe (1:2 brew ratio) this
means that even for a very fresh coffee 1h after roast and 2min
after grinding the water can add another 20 % to the carbon
dioxide already contained in the coffee grounds.
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Summary
• Using equivalent units (e.g. ppm CaCO3 or °d) is paramount to facilitate the understanding and application of insights on water
• With regard to sensory aspect the acid buffer capacity should be referred to as alkalinity (“carbonate hardness” is not necessarily equal to it!)
• Most waters in central europe have an alkalinity slightly lower than total hardness – and with respect to coffee they are several fold too hard
– “Moving left” into the range of high total hardness and low alkalinity require the introduction of new cartridges (which exist in other industrial applications)
• As long as alkalinity is kept above 40 CaCO3 the water is sufficiently buffered to avoid the risk of corrosion
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Thanks for your attention