BRITA’s Head of Organoleptic Department Birgit Kohler explains how different water filter technologies affect the flavour of coffee.
Besides using different coffee beans and methods of preparation, water has a crucial impact on the flavour of coffee. Using water with an unfavourable chemical composition can negate the time, money and effort gone into defining and achieving a particular flavour profile, resulting in a sensory experience that falls short of expectations. It’s therefore important to understand not only how different filtration technologies work, but how they affect coffee’s flavour to either amplify the desired sensory effects, or eliminate undesirable ones.
The principal characteristics of the main water treatment technologies are activated carbon filtration, decarbonisation, softening, total demineralisation, reverse osmosis, and mineralisation. Let’s break them down while focusing on the sensory aspects of how they influence coffee flavour.
Activated carbon
Activated carbon is a porous, fine-grained carbon. It is obtained by charring a natural carbonaceous material such as wood, peat, anthracite, or coconut shells and then ‘activating’ it in a thermal process. This second step causes it to develop a large number of pores, greatly increasing its internal surface area and enabling the material to attract and hold large amounts of other substances. BRITA uses food safe activated carbon made from coconut shells.
Activated carbon is able to significantly reduce the organic substances in water that have an unpleasant odour. These include, for example, metabolic waste products from the bacterial decomposition of plant residues such as foliage. An example is geosmin, which can impart a stale earthy smell to groundwater and consequently also to drinking water.
Depending on its concentration, this substance can also induce an atypical off flavour in coffee that is perceived as ‘wrong’. Activated carbon is also used as a catalyst for reducing chlorine. Chlorine has a distinctive odour and can, in sufficiently high concentrations, be perceived in coffee. But even when the chlorine content is quite low, reducing it is a very important prerequisite for ensuring good-quality coffee. Chlorine is highly reactive and can combine with organic substances in the coffee, altering their structure and sensory properties.
Due to the chemical and sensory changes that chlorine undertakes when reacting with coffee constituents, the resulting undesirable changes in the aroma profile aren’t attributed to the chlorine, despite having caused them. That’s why it’s always advisable to filter water – including so-called soft waters – with activated carbon.
Decarbonisation
Decarbonisation, also known as partial demineralisation, is a term applied to all water treatment methods that reduce carbonate hardness. How does this affect coffee’s sensory attributes? Acids, including those in coffee, are by definition, substances that possess and readily emit hydrogen ions. If water is not filtered or decarbonised, the hydrogen carbonate would react with the hydrogen ions of the acids present in the coffee. The remaining part of the coffee acid left after shedding the hydrogen ions can lose its sour taste in the process. The more hydrogen carbonate is available to react with the hydrogen ions of the coffee acids, the more coffee can lose its sourness.
Softening
Softening refers to all water treatment processes for reducing total hardness (the sum of carbonate hardness and permanent hardness).
The more perceptible roasted aromas and increased bitterness result in a coffee flavour that is often referred to as ‘typically Italian’. Those who don’t enjoy this flavour profile can additionally decarbonise the filtrate. This substitutes hydrogen ions for part of the sodium ions in the water. Fewer sodium ions and hydrogen carbonate are then available, which can reduce roasted aromas and bitterness, and allow sourness to develop better.
Total demineralisation
Total demineralisation is a technology that involves the combined use of both cation and anion exchangers. As a result, it almost completely eliminates the cations calcium, magnesium, sodium and potassium, and the anions hydrogen carbonate, sulphate, chloride, and nitrate. Reducing these minerals in the water can also mitigate any adverse effects on the coffee’s balance of flavours.
In sensory terms, however, such chemically mineral-free water isn’t ideal. It can result in coffee with excessive sourness and weak aromas. To let the aromas fully unfold while reducing the coffee acids somewhat, a certain amount of minerals must be present. This is commonly ensured by mixing the filtrate with a small quantity of unfiltered water from the same source via a bypass. This comes at a price, however, as the added unfiltered water can also contain other, undesirable high amounts of chloride or sulphate. Whether or not a bypass solution will work as intended, dependson the types and concentrations of these unsavoury substances.
Reverse osmosis
In reverse osmosis, water is pressed through a membrane. The membrane’s pores are so small that only water molecules, which are very tiny, can pass through. The minerals and organics dissolved in it are all too large to wiggle through. The filtrate therefore consists almost exclusively of pure water.
This somewhat more complex technology can always be deployed if other, simpler methods fail to achieve the desired effect or there is no other way to resolve a water-related sensory problem. Its advantage is that regardless of the original water, almost all other molecules are removed leaving only chemically pure water.
The drawback is that like total demineralisation, it yields water that isn’t optimal for preparing coffee. Here too, it’s a good idea to add a small amount of unfiltered water to the filtrate via a bypass. A more elegant alternative is to additionally install a post-mineralisation filter to make sure that only acceptable amounts of the desirable calcium and/or magnesium ions and hydrogen carbonate enter the filtrate.
Mineralisation
When coffee is made with water that is almost completely free of minerals, coffee acids can dominate its flavour. This can be offset by intentionally adding a small amount of calcium and/or magnesium ions and hydrogen carbonate to enhance the balance of flavours while slightly reducing the sourness. In solutions that use reverse osmosis, mineralisation is an alternative to a bypass and even superior to it in purely sensory terms, as it only channels the desired minerals into the filtrate.
Many mineralising filters use grains of stone containing calcium, magnesium, and carbonate. When these minerals come into contact with slightly acidic water, they dissolve into it. It therefore makes good sense to insert a further, pH- reducing filter (such as a decarbonisation filter) ahead of the mineralisation filter to ensure that a sufficient quantity of the minerals is dissolved.
Suitable filter equipment can be used to purposefully adjust the chemical composition of the water and optimise the flavour of coffee as a result. BRITA has a variety of filtration technologies available for accomplishing this, and can be counted on to give sound advice on matching flavour preferences.
For more information, visit www.brita.com.au
This article appears in the October 2023 edition of BeanScene. Subscribe HERE.
