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Hydrochemistry on the Rocks


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It is considered one of the oldest foods and most appreciated beverages of the world – chemical remains were found on fragments of a more than 4.000 old jar, the Mesopotamians guaranteed its purity by death penalty and the old Egyptian considered it an essential part of the afterlife – the preferred drink of the gods of the Vikings – and today of geologist, known also as beer.

Geologists love beer for a simple reason: it makes you think a lot about geology…(and as a popular side-effect it is tasty).

The quality of alcoholic drinks (final results of the fermentation of an extract of cereal grains or fruits) and especially beer is defined by five factors: the flavour, the alcohol content, the colour, the head retention and the clarity. These factors depend strongly from the used ingredients – one of the most important is water and the chemistry and quality of water depends strongly from the geology and hydrology of the source region.
The brewing process involves great quantities of this special ingredient and many breweries use private springs or wells to satisfy their needs, referring even to the supposed water quality or purity in their advertisements. Already in medieval times beer was a more trusted beverage than simple river water.

Fig.1. A natural occurring spring – the position and discharge of a spring is significantly influenced by the overall geology and tectonic situation of a catchment area.

Natural waters contain four cations particularly significant for the brewing process: Calcium (Ca), Magnesium (Mg), Sodium (Na) and Potassium (K).

Calcium stabilizes the enzymes used by the yeast to break down the starch into sugars or sugars into alcohol, this element also precipitates phosphate – also present naturally in the water – correcting the pH-value of the mash and supporting microbial activity. Magnesium has a similar effect and also controls the phosphate concentration, however too much magnesium can give the beer a bitter taste. Also sodium and potassium can ruin the taste and more importantly both elements can have a strong laxative effect on the heavy drinker.

The concentration of these cations in the water depends strongly from the geology of the catchment area and the source rocks of the used springs or wells.
In regions with carbonate rocks the springs show a high concentration of calcium and magnesium. Often the concentration is so high that the control of the pH-value of the mash becomes a major problem. The low pH makes only relatively sweet beers possible, even if by selecting carefully other ingredients still variation is possible – one bad luck of the Irish, with an island dominated by Carboniferous limestone. However the chemistry of the used water made it also possible to brew the well-known dark stout of Dublin.

Also the concentration of anions influences the final product. Sulphate (SO4), deriving from evaporitic rocks, can give the beer a desired bitter flavour by supporting the release of bitter oils from hops and reacting with magnesium to produce magnesium sulfate (Mg(HSO4)2), a bitter tasting salt. Also water from springs with a high concentration of chloride (Cl) and sodium (deriving from salt deposits) give to the beer a salty to bitter flavour – however in the correct proportions the sweetness of the chloride ion can prevail, resulting in the unique taste of a classic ale.

In contrast regions with sandstone-formations or metamorphic rocks are characterized by springs and groundwater with a low concentration of dissolved minerals and ions. The lack of the previously mentioned ions in the brewing process results often in a beer with less distinct flavour. To compensate this disadvantage the beer has to be fermented for longer time (incrementing also the alcohol strength of a beer), preferably in a dark, cool environment like a cave. The denomination of the Pils or Lager, classic beers coming from Central Europe, derives from this “storage” technique.

But not only beer, also the quality of the “uisge beathe” – Gaelic for “water of life“, today known as whisky or whiskey – depends from the used water, even if the distillation process is more important and enhances or minimizes certain effects of the original water chemistry.
Like in the brewing process of beer the chemistry of the water influences the extraction and fermentation of sugars and probably also the taste of the final product (however there is apparently less research done on this drink). Tradition affirms that water coming from granitic rocks is the best for the whisky production, however most distilleries in Scotland are situated on shale- and sandstone-formations or metamorphic schist. The minerals composing these rocks are almost insoluble in water and the “soft” groundwater of these regions is therefore only slightly mineralized.

Fig.2. Distribution of some of the whisky distilleries in Scotland projected on a geological map compiled by geologist A. Geikie in 1887. Scotland is characterized by southwest-northeast trending tectonic units, formed mostly by metamorphic rocks in the north and sedimentary rocks in the south. Distilleries are mainly found in regions lacking carbonate rocks and whit soft groundwater.

Geology can indirectly also influence the pollution of the water used in the brewery process. The weathering of the Old Red Sandstone, formation found in many regions of Scotland, produces fertile soils used for agriculture purpose. The aquifers located in this formation are therefore often contaminated with nitrate infiltrating from the surface.

Today, with the help of effective water pumps and transfer of water over long distances, the role of local geologic conditions is less important than in the past. Many wells or springs – especially in industrialized areas or regions with intense agriculture – are also contaminated with pollutants or overexploited and no longer in use.  To overcome the shortage some breweries are experimenting even with new technologies, for example water that was previously artificially deionized and subsequently “customized” to a desired chemical composition – with the advantage of improved hygiene and better quality control – however with the disadvantage to lose the fun of discovery of the geologic information concealed inside the drink…

Bibliography:

CRIBB, S.J. (2005): Geology of Beer. In Selley, R.C.; Cocks, L.R.M. & Plimer, I.R.: Encyclopedia of Geology: Elsevier Academic Press: 78-81
CRIBB, S.J. (2005): Geology of Whisky. In Selley, R.C.; Cocks, L.R.M. & Plimer, I.R.: Encyclopedia of Geology: Elsevier Academic Press: 82-85
GEIKIE, A. (1887): The Scenery of Scotland viewed in connection with its Physical Geology. Macmillian & Co., London: 481 + 1 plate

David Bressan About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.



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