water for coffee extractionscae.com/images/pdfs/ast-live-2016/water-composition-for-coffee.pdf ·...

1Marco Wellinger

Dr. Marco WellingerZurich University of Applied SciencesICBC - LSFMWädenswil, [email protected]

Water for coffee extraction: Composition, recommendations and treatments

2Marco Wellinger 2Marco Wellinger

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


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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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


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Mg2+ Ca2+

HCO3-

Na+ K+

Cl- NO3- SO4

2-

Total hardness ≈ carbonate hardness Non-carbonate hardness is zero

Alkalinity

«Not hard» carbonate


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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


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


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


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).


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.


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


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


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.


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


Thanks for your attention

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