Understanding Whisky Production Unit 2: Raw Materials
Chapter 4: Water in Distilling: Sources, Mineral Chemistry, and Treatment
How surface burns, aquifers, and process water affect mash pH, enzyme activity, yeast metabolism, cooling efficiency, and spirit cut.
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Water enjoys a sterling reputation in whisky marketing, usually pictured tumbling down a heather-clad glen beneath an overcast Scottish sky. In the cold light of chemical engineering, however, water performs two wildly different jobs: a small fraction is consumed in mashing and reduction, while the overwhelming majority simply circulates through cooling condensers to pull heat out of boiling alcohol vapour.
For the water that actually enters the mash tun, mineral chemistry is paramount. Dissolved calcium and magnesium ions quietly adjust the acidity to the exact pH range where mash enzymes thrive. Heavy metals like iron, meanwhile, are treated as public enemies, capable of turning the mash an unappealing shade of black and poisoning the yeast.
Sources of Water
A reliable and abundant supply of water is essential for our production processes to occur. Beverage plants are usually located close to a reliable water source. We obtain our water from one or a combination of the following sources: surface water, ground water or municipal (public) water. These water sources have different attributes and compositions. Each type must be treated differently as it arrives into our plant.
As per the preface, our supply of water is ever diminishing. Many plants rely on a public water supply, which is pre-treated and thus (should be) already potable. Plants may also have their own well or borehole water supply. A combination of these water sources is often used to limit the risk of running out of water.
We have now mentioned the three main sources of water. Let us consider them in more detail. We must note that we can generalise these three water sources, however every source is very variable. Water analysis is thus vital so that we can understand the quality of the water we are using.
Surface Water
Surface water is the most recognisable water source that we use. It comes from rainwater and snowmelt run-off from rivers and lakes, in natural surface water catchment areas.
70% of the earth’s surface is water. 97% of the earth’s water is salt water in oceans. 2% is fresh water in ice caps. 0.6% is ground water (boreholes and springs). 0.4% is fresh surface water (rivers, lakes, reservoirs).
We, as humans, have engineered our environment and built dams in these natural catchment areas to maximise the efficiency of water collection and storage.
Surface water is typically soft (described later in this chapter), with a relatively low mineral content compared to ground water. However, it generally has a higher organic loading, as it is open to the atmosphere. It can therefore also be present at higher temperatures, which promotes the existence of organic material and supports microbiological contamination. Furthermore, surface water is open to pollution from towns, cities and from agricultural run-off water, which contains chemicals from fertilisers and pesticides.
Ground Water
Fortunately for us, there is more fresh water beneath the earth’s surface than on it. This is important, as we have seen that surface water can be readily contaminated and polluted. It can also have a high organic loading. This is compared to ground water, which typically has low organic and microbiological content due to lower oxygen and temperature levels. Ground water can have higher mineral and metal ion content, as the water is situated in bedrock, which often has a high iron and calcium content.
Ground water is considered purer than surface water. As mentioned previously, it has lower levels of contaminants and organics. This is often because the water has been well filtered as it passes through the earth’s layers.
Municipal (or Public) Water
OK, so this is not an original source, unlike our previous two examples. However, it is a definitive source that can be used. It is governed by very different ‘rules of supply’ and has different constituents and properties. It must therefore be treated differently. The treatment will depend on the water’s constituents, which in turn depend on the municipal water source, be it from surface or ground water.
In the Scotch Whisky industry, the water is not treated (addition of minerals), but minerals may be removed, or pH corrected.
The following table compares the three water sources against the key attributes that we have been discussing thus far:
| Key Attributes | Surface water | Borehole water | Public water |
|---|---|---|---|
| Consistency of supply | Variable | Good | Very good |
| Temperature | Seasonal | Constant | Constant |
| Turbidity | Variable to high | Low | Low |
| Colour | Variable to high | Low | Very low |
| Carbon dioxide | Low | Usually present | Very low |
| Odours/taints | Variable to high | Low | Low |
| Mineral content (hardness) | Variable to low | Variable to high | Source dependent |
| Iron content | Low | Usually present | Low |
| Microbiological content | Variable to high | Low | Low |
Potable Water
As we have suggested, water is the “stuff of life”. We know what ‘good and bad’ water looks and smells like. Potable water is that which is fit for human consumption. Of course, we have to do a full laboratory analysis. There are four main potable water attributes: colourless, clear, tasteless and odourless. However, many more parameters exist, in fact the EU regulations list 48 in total.
Water Colour, Clarity, Taste and Odour
‘Clear’ refers to the lack of turbidity, as shown in the above table. In other words, there must be neither haze nor any particulate matter in our water. Colourless refers to the absence of a hue or tint, and not the turbidity. Turbidity can impart a colour, but we can also have coloured water with no turbidity at all. Coloured water usually takes on a milky white hue due to the presence of calcium and carbonate salts, or a brown colour from the soil (especially in river water). These salts can lead to haze formation in the final product when used as reducing water at casking or as final reduction prior to bottling.
Potable water is tasteless and odourless, and this is how we need our product water. In addition, we can organoleptically (using our senses; sight, taste, smell and touch) detect taints in our water.
Contaminants and Taints
Let us now look at contaminants and taints. This is a big topic in its own right, but for our purposes, we will cover the more common taints that can cause big problems within our product water.
These taints (odour or taste) come from contaminants. As we have mentioned, surface water is much more susceptible to these contaminants, compared to ground water. These contaminants usually come from pollution and agricultural run-off. We must also note that these contaminants can be present in public water, carried over from the municipal water treatment chemicals and processes. We will cover some of the more prevalent (common, with large impacts on taste and odour) contaminants.
Chlorophenol from the reaction of the chlorine with phenolic compounds, is intensely flavour active and can be detected at levels < 1 mg/L, giving a medicinal taint.
Trihalomethanes (THMs) are extremely flavour active compounds (have very low flavour thresholds) and are formed from the chlorination of water, containing organic (humic) acid (e.g. trichloro-methane). They are also suspected carcinogens and levels at < 100 μg/L are thus specified.
Let us now explain agricultural run-off using a bit of science. Nitrosamines are also suspected carcinogens. These compounds are formed from the nitrites and nitrates present in pesticides and fertilisers predominantly used in agriculture. They are represented as Apparent Total Nitroso-Compounds (ATNCs). These compounds also have legislated limits, typically at levels of < 20 μg/L. This limit refers to the final product, not the water itself.
Water can contain a whole host of pathogens (disease causing micro-organisms). Alcoholic beverages usually do not contain pathogens due to their attributes, such as a low pH and high alcohol concentrations.
This is a big topic, thus we will again focus on the requirements of our product water. The prime reason for treating our water is to eliminate microbiological content. We have seen (from the previous table) that surface water is prone to microbiological contamination, and so a public water supply’s prime treatment is to affect a degree of sanitisation to kill the microbiological content.
It may be surprising to note that sterility is not normally achieved! Many of our products and processes achieve sanitisation (commercial sterilisation), but not sterilisation, as this is good enough to make the products safe for human consumption.
However, all municipal water has to pass very strict, and usually legislated, specifications.
Most water used in distilleries does not have to meet potable water standards. For example, condenser cooling water does not.
Let us mention a few key scientific names that we should know about, such as E. coli ( Escherichia coli ). This is one of the most common bacterium that can contaminate our water, especially where it’s extracted below arable land used by livestock. Other well-known contaminants include the Hepatitis A virus , Cholera, Legionella, Cryptosporidium, Giardia lamblia and salmonella bacteria.
A typical potable water microbiology specification is as follows:
- Total coliform bacteria < 1 cell per 100 mL
- All micro-colonies < 10 cfu (colony forming units) per mL
The above specifications are very strict. These micro-organisms can form contamination of many millions per mL, as they reproduce exponentially in very short periods of time. Remember that sterility is not needed and thankfully so, as it is a very time consuming and costly process to do so.
Categories of Water and their Attributes
OK, so we have looked at the requirements of product water, yet surely water is water? No - this is not so. Let us now briefly summarise the different categories and types of water that we can find in our plants. here, we are focusing on the product water used as a raw material. We will thus not go into the treatment details of the various water types here, as this will be covered in the utilities lesson.
The following main water categories are based on their usage (and their initial treatment as they enter the plant). This provides us with a base definition, from which we can later differentiate specific water types based on their specific uses and requirements. These usages usually do require further treatments, but they are carried out on the base water that is categorised below.
The actual names of the categories and types can, and do, vary across plants. However, we have found that they usually resemble the following classifications:
Water categories:
- Product water - interacts with the product
- Process water - assists in the functioning of various production processes
- Service water - provides water to non-production (service) systems
Product Water and Types
Product water is the water that interacts with the product, as either an integral ingredient, or by coming into direct contact with our product as dilution water. As mentioned, there are a variety of water types that can be included within this category, such as production, reduction (water added before maturation/blending) and deaerated water.
Let us briefly introduce the other main types of water and their attributes, as this will help us to better differentiate product water.
Process Water and Types
Process water is used to carry out production processes, such as for the cleaning in place (CIP) of vessels, and also as cooling water in heat exchangers, worm tubs and condensers. It is however not fully treated water, as it should not be exposed to the product.
Service Water and Types
This water is sometimes raw, incoming water, or is sand-filtered on entry to the plant, depending on source quality. It can also be chlorinated and UV treated to initially reduce micro-organisms. This water does not have to be dechlorinated, as it is for non-production services. It thus should not come into contact (or preferably anywhere near) with the product itself. This water is used for refrigeration, ablutions, grounds water and cooling tower water.
We will specifically mention cooling tower water and boiler water here, as they are the two big water users in our plants. Furthermore, they do usually require further treatment. Cooling tower water is further treated with biocides to especially prevent the growth of Legionella bacteria. Boiler water is further treated to produce softened water, which prevents scale formation. Therefore, most water boiling (steam production) plants have a water softening plant as an integral part of their design and operation.
Process and service water will be discussed in more detail in the Energy and Environment lesson.
The Mineral (Ionic) Content of Water
We will now cover a significant attribute of our product water. Can you guess what it is?
Yes, we are talking about pH!
We have decided to include this very important water attribute in our discussion on mineral content, as it is indeed influenced by the presence of minerals. It also indicates the water’s source - whether it is surface or ground water.
As a measure of the water’s acidity or basicity, we usually target neutrality. We do prefer slightly acidic water, if not an exactly neutral pH of 7.
PH is a measure of hydrogen ions on an inverse logarithmic scale. pH 0 is very acidic and pH 14 is very alkaline. Therefore, acids have many hydrogen ions and alkaline solutions have very few.
Water Hardness
The most common attribute of water’s mineral composition is that of water hardness. This can simply be described as the water’s ability to form a lather with soap. Very soft water forms a heavy soap lather, whilst hard water does not. Hard water becomes quite difficult to clean with when using soap!
So what is water hardness, and what has it got to do with the mineral content of water? Water hardness comes directly from the ionic composition of water, made-up of various cationic (positively charged) and anionic (negatively charged) elements. We will cover the fundamental principles of water hardness, as it pertains to our product water quality. Furthermore, this will help us for later study, when we consider how to treat it.
Water hardness is mostly dependent on the presence of calcium and magnesium metal ions in the water. We have two types: that of temporary hardness and permanent hardness. Permanent hardness is that which remains after boiling, whereas temporary hardness is removed by boiling.
Permanent hardness causes hard scale in boilers, pipework and heating surfaces, drastically reducing their heat transfer coefficients and throughput. This loses money through the additional heating costs required due to inefficient heating. In addition to this, it is very difficult to remove, thus it can cost time and money to get rid of this scale. Permanent hardness is mainly formed from the salts (compounds) of calcium and magnesium sulphate, chlorides and nitrates; they have little effect on the pH of the water.
Temporary hardness forms soft scale, and is more easily removed by a variety of simple treatments. This soft scale is mainly formed from the salts (compounds) of calcium and magnesium carbonates and bicarbonates. Water with high temporary hardness is higher in pH and more alkaline, with a higher buffering capacity.
Let us quickly review a couple of other measures that are relevant to the hardness and the mineral content of the water. Total hardness is a measure of the total calcium and magnesium hardness, measured as a carbonate composition of the water. Calcium hardness indicates how much hardness is due to the presence of the calcium salts only.
We have hinted at the relationship between mineral content, pH and alkalinity. Total alkalinity is measured as an indication of the total content of carbonates and bicarbonates, as these compounds cause soft scale, which does affect pH and alkalinity.
Key Water Ions and Their Importance
Let us consider some ions that typically hold importance in alcoholic beverage production, especially those utilising a cereal mashing process.
Water Conservation and the Reliability of Supply
Lastly, but by no means least, is the supply and conservation of water. In addition to water becoming a scarce commodity, it is also an expensive raw material. From an economic and business point of view, we need to take care of this precious resource to ensure that we can stay in business.
To be able to manage our resources, we need to measure them. Beverage plants typically measure their water usage as a ratio in terms of litres of water used per litre of product produced.
Water conservation begins with waste reduction. From here, we can then optimise plant and processes to better utilise water. Let us look at ways in which plants can achieve this using our main water categories:
Water waste reduction:
Product water waste: leaks and excess vessel flushing and draining
Process water waste: leaks and excess CIP usages and dumping of those service tanks.
Service water waste: leaks, condensate loss and excess cooling and hose use
Once we have reduced waste, we can then optimise water usage. We can also implement strategies such as monitoring and targeting (M&T), which assist in the management of water conservation. These strategies can include the following:
Monitor and analyse water use to establish trends.
Target the areas for improvement, and establish action plans.
Implement sustainable improvements to establish best practice.
Key Takeaways
While cooling capacity dictates how hard a distillery can run in the summer months, mineral content in the process water governs mash enzymatic efficiency, fermentation vigour, and the eventual clarity of the spirit.
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