Water is an essential element for life. After all, without water we wouldn’t have coffee, would we?! But seriously, how much do we really know about this element? Let's analyse its composition a little deeper as well as the things we need to keep in mind when preparing a good coffee.
Water is a “living” element and is always in motion. It is the only element in nature that we use every day that can cross three different physical states: liquid, solid and gaseous. Its total volume on our planet has not changed for millennia; all that varies is the balance across these three states. What is the first thing that comes to mind when we think of water? Obviously its formula: H2O. However, water generally only appears in this pure form in everyday life when it is in a gaseous, vapour state – and generally not when we use it to make a coffee. Dissolved substances are bound to this molecular compound making water "heavy" and "tasty". So, despite its transparency, water hides several essential elements for the preparation of a good coffee! Let’s now see what the main substances are that compose water - both from the tap and the bottle - as well as its influence on the extracted coffee.
As you probably already all know by now, water is the principal ingredient in coffee - about 90% in an espresso and 98% in filter coffee. However, it also acts as a solvent during the preparation of the coffee so it plays a double role. It influences the taste and the extraction of coffee; the quantity we transfer to the cup. Whether it is espresso or filter coffee, the soluble substances present in coffee beans must be dissolved in water to release all their organoleptic properties. For this reason, water must be a professional’s closest ally and for this to happen we need to understand its most important characteristics.
Whether it is water coming from the local water supply or from bottled water, its main elements are:
- natural minerals; coming from the ground or absorbed during its journey from source to tap
- chemical substances; used to treat water to make it microbiologically pure and free from bacteria, mainly chlorine
It is this chlorine that is coffee’s number one enemy due to its oxidizing effect that alters the sensory structure of the coffee making it more bitter and, in the case of espresso, bleaching the creamy layer on the surface of the coffee. To eliminate it one needs to use active carbon filters or simply leave the water to rest for a period of time, given that chlorine tends to evaporate rather quickly. With respect to the dissolved minerals, these are mostly calcium and magnesium which are responsible for the so-called “hardness” of the water. Its overall hardness is the sum of “permanent” hardness - the quantity of minerals resulting from prolonged boiling - and “temporary” hardness - also called alkalinity - consisting of carbonates and bicarbonates of calcium present before boiling. A correct extraction will be determined by the balance between these solids and carbonates. Total hardness is measured in French degrees (° f, not to be confused with °F which are instead degrees Fahrenheit) where a French degree corresponds to 10 mg / l or ppm. The challenge is to accurately determine these values present in the water when we prepare a coffee.
With respect to water coming from the public water supply, the most precise method is to have it analysed by a specialized laboratory. It is certainly not the most practical or economical, but in doing so we can be guaranteed accurate information from where to start. A cheaper alternative is to get this information from the water bill (as declared by the supply provider) or finally to buy a water analysis kit, readily available for purchase at low cost.
For bottled water it is necessary to know how to read the label. There are two pieces of information to pay attention to: fixed residue and conductivity. Very closely related, these values indicate the average amount of dissolved salts in one litre of water and this differentiates heavy water from light water. For the purposes of convenience, we generally take the value of the fixed residue as being equal to Total Dissolved Solids (TDS, which is not entirely precise since TDS also includes salts and volatile organic material).
The ideal value of total hardness obviously depends on the amount of substances one wants to extract into the cup, the Specialty Coffee Association (SCA) in a recently published research on water quality has defined an ideal range as being between 50 and 175 mg / l, with temporary hardness between 40 and 75 mg / l. pH value on the other hand indicates the acidity or alkalinity (basicity) of the drinking water and is measured on a scale of 0 and 14 pH. The pH of drinking water must be between 6.5 and 8.0 pH, therefore as neutral as possible. Non-neutral pH values are due to chemical elements present in the water. Lower or higher values indicate that the water is polluted by strong bases or acids. Values of pH higher than pH 11 or lower than pH 4 are to be considered hazardous to one’s health. The carbonates - the “temporary” hardness – other than helping to produce a correct extraction, also guarantee a stable pH.
THE IMPORTANCE OF FILTERING COFFEE
When preparing coffee, water is very influential from a physical and chemical standpoint. The first of the two concerns what happens during extraction due to the passage of water through the ground coffee. The second concerns the dissolved substances that generate the different organoleptic sensations that make the coffee either more or less pleasant to drink. Consequently, water plays a dual role in coffee as both solvent and main ingredient. Customers expect that the quality of coffee is always consistent, so it is essential to monitor the “behaviour” of the water used. Equally essential, to ensure uniformity of taste and extraction, is correct filtration in order to better manage the dissolved solids content, the as-mentioned TDS. The presence of calcium and magnesium, as mentioned previously, determines a greater or lesser total hardness and, given both elements have a positive electric charge (chemically speaking), when they are dissolved in water they attract most of the aromatic compounds which are themselves negatively charged. A certain amount of these minerals are therefore essential to extract solid substances from ground coffee. In particular magnesium, attracting the smallest and most oxygen-rich aromatic molecules, has a greater effect on extraction. Carbonates and bicarbonates instead balance the overall acidity levels. Depending on the extraction method used, espresso or filter, solids are needed that are more and less chemically charged, respectively. This is because the contact time between coffee and water is less and more, respectively - 30 seconds for an espresso, several minutes for a filter. However, what is fundamental for the quality of extraction in the cup, is starting with cold, clean, neutral water. In summary, water that is too “light” will not have the strength to transfer all the aromatic substances that the coffee has into the cup. Conversely, heavy water may be too "charged" and therefore not able to bind itself with other substances.
Until a few years ago filters were installed simply to protect machines from calcium deposit and it is only recently that the influence of water on taste and extraction in the cup has been considered. These are the most commonly used filtration systems:
- Softeners: through an exchange with sodium molecules, they act on the hardness of the water removing calcium and magnesium, without affecting alkalinity. Doing so reduces limescale, but this significantly reduces the control we have on taste and extraction, above all in extracting acidity.
- Cartridges with activated carbon: they intervene and control the alkalinity, regulating the presence of carbonates and bicarbonates. Depending on the type of cartridge installed one can choose how many - and which - substances to extract.
- Osmosis: completely removes the presence of solids through a physical process in which the liquid is pushed and filtered through a porous membrane. This essentially produces distilled water which must therefore be re-mineralized. It could be suitable in very extreme situations or if a consistent type of water is required. In practice it effectively allows one to create a personalized "recipe" of solids.
Determining the best filtering system depends on the composition of the water being worked with and what is desired when transferring to the cup.
>> If you are interested in this subject take a look to our Brewing courses!
Finally, did you know that about 140 litres of water are needed to produce a cup of coffee? This is based on the water footprint the average quantity of water consumed during all phases of the production chain.
Only 1% of the water on our planet is drinkable, and half of this is polluted.
In Cameroon, some organizations are supporting the development of water networks to provide drinking water and support the production of coffee.
The Fondo Ambiente Italiano (FAI) decided to dedicate the 2018 National Convention to the theme of water “…as a precious resource to be defended” and subsequently launched the #salvalacqua campaign.