Finding the Best Water for Brewing Kelloo Coffee with a V60
At Fission and Bloom, we are constantly experimenting with ways to improve the coffee brewing experience. One of the most important variables in brewing coffee is the quality of water. Water makes up more than 98% of your cup of coffee, so it’s no surprise that the mineral content, pH, and overall composition of the water you use can have a big impact on the taste. Recently, I conducted a simple taste experiment with several different waters to find out which one produced the best flavour when brewing our Kelloo coffee using the V60 pour-over method.
For this experiment, I brewed the coffee using five different sources of water: Voss, Royal Deeside, Highland Spring, Evian, and my own filtered home water. Each cup revealed different flavour profiles, with notable variations in acidity, sweetness, and overall balance.
The TLDR version is, Voss still water made a very pleasant tasting coffee.
The Waters I Tested
Before diving into the flavour profiles, here’s a quick look at the key mineral contents of the waters I used. The mineral content of water plays a crucial role in the perception of the coffee flavours after extraction. I will discuss in more detail in a later post the various sources of information/studies on this topic. Some believe that minerals like calcium and magnesium bind to flavour compounds, helping to extract the desirable flavours in coffee. Too much or too little of these minerals can cause bitterness, dull flavours, or flatness. For now, I continue to use this concept of “over extraction” when I describe flavours of bitterness and wateriness and/or flatness, but because I have not assessed the differences in amounts of various compounds, I do not know if there is any differences in compounds extracted from the coffee, just that the perceived taste is different.
| Water | Total Dissolved Solids (TDS) | Calcium (Ca) | Magnesium (Mg) | Bicarbonate (HCO₃) | Sodium (Na) |
|---|---|---|---|---|---|
| Voss[1] | 40 mg/L | 2.7 mg/L | 0.61 mg/L | <20 mg/L | 3 mg/L |
| Royal Deeside[2] | 60 mg/L | 4 mg/L | 3 mg/L | 26 mg/L | 6 mg/L |
| Highland Spring[3] | 170 mg/L | 40.5 mg/L | 10.1 mg/L | 150 mg/L | 5.6 mg/L |
| Evian[4] | 345 mg/L | 80 mg/L | 26 mg/L | 360 mg/L | 6.5 mg/L |
| BIBO (Filtered)[5] | 150 mg/L | N/A | N/A | N/A | N/A |
*TDS may have been reported for different temperatures; Evian and Highland Spring were reported at 180 degrees Celsius. 1. https://vosswater.com/water-quality-report/; 2. https://www.deesidewater.co.uk/trade-and-export/bottled-water-range/; 3. https://highlandspring.com/product-range/spring-water/; 4. https://www.evian.com/en_gb/our-water/water-attributes/; 5. Tested using a TDS meter. All websites accessed 8th October 2024.
The table above summarises the mineral content that is important for coffee extraction. It is said that calcium and magnesium play crucial roles in coffee brewing because they aid in the extraction of organic compounds, while bicarbonates help neutralise acids, balancing the acidity and smoothness of the cup. Water that is too high in TDS can over-extract the coffee, leading to bitterness, while water that is too low in minerals might under-extract the coffee, resulting in a weak flavour.
In this taste test, my aim is to suggest a readily available bottled water option in the UK, rather than confirm whether the observed differences are solely due to mineral content. However, I will attempt to draw some connections between what I taste in the various cups and the mineral composition listed in the table above. It's important to note that the flavour descriptors I’ve used are meant to highlight the differences between the cups and not necessarily to define the coffee itself. Additionally, the results of this test are specific to the particular coffee bean used, its roast profile, and the brewing method. For instance, if I mention tasting "dark chocolate" in one cup, it doesn't imply that the water always brings out that flavour in every coffee — it can only highlight flavours that are already present in the bean.
Tasting Notes and Results
Voss
The cup brewed with Voss water was balanced and mild. It had a subtle citric acidity and a touch of brown sugar sweetness. The flavours were gentle and harmonious, with no overpowering roast notes. This cup was smooth and well-rounded, with a light, floral acidity that made it enjoyable to drink.
Acidity: Mild, citric, balanced
Sweetness: Brown sugar
Aftertaste: Subtle, smooth, with no dark roast bitterness
The low mineral content of Voss water, particularly its low calcium and magnesium levels, posibly contributed to the clean, mild taste of the coffee. The low bicarbonate level maybe also helped maintain the balance of acidity without muting it.
Royal Deeside
With Royal Deeside water, the coffee's acidity and sweetness were more pronounced. However, as the cup cooled, there was a noticeable green apple-like flavour, which hinted at the presence of malic acid. Compared to the Voss cup, this coffee felt more watery and dry, with a papery aftertaste.
Acidity: Pronounced, a bit harsh after cooling
Sweetness: Present but less than Voss
Aftertaste: Papery, dry
The mineral levels in Royal Deeside water is slightly higher than Voss, which may have contributed to the more intense and sharper acidity. The water's overall mineral content, though still low, was enough to bring out some of the fruity flavours, but it lacked the balance that Voss provided.
Highland Spring
Highland Spring brewed a coffee that was a bit astringent and flat, with a sharp acidity. The initial taste had some interesting dark sugariness, but as it cooled, it developed some bitter notes typical of a darker roast. The coffee also had a nutty and chocolatey aftertaste that was not as bright or floral as the Voss or Royal Deeside cups.
Acidity: Sharp, short
Sweetness: Dark sugar, but fades quickly
Aftertaste: Bitter, chocolate, and nutty
Highland Spring has the highest mineral content of the three bottled waters tested (more on Evian later), particularly in calcium and magnesium. This likely contributed to the more astringent and bitter notes, as the higher mineral content can possibly over-extract (or enhance our perception of) flavours, bringing out bitterness and muting more delicate, floral notes.
Filtered Home Water (BIBO)
The cup brewed with my home-filtered water was more bitter than the others. The astringency was more noticeable on the tip of the tongue, and overall, the flavour was flat compared to the Voss brew. As the cup cooled, the flavour became even more dull, with no distinct acidity or sweetness coming through. (Remember, I am trying to exaggerate the differences between the cups, and though I use terms here that might sound negative, it is subjective and another person might prefer the flavours of this cup. For example, someone might like that this was more toasty and less acidic, in fact, this is more like the coffee we know.)
Acidity: Mild, overshadowed by bitterness
Sweetness: Minimal
Aftertaste: Flat, astringent
While the filtration system removes most impurities, the profile of this water resulted in a cup that was not as harmonious as the cup with Voss; it was more roasty and had flavours of dark/burnt sugar. Because the BIBO provides hot filtered water at temperatures I set, this is the water I tend to use when testing many coffee samples. It is therefore interesting to note that with a different source of water, I could roast darker than the beans used here without believing I was over-roasting.
Evian
The cup brewed with Evian water was immediately unpleasant. It had an overwhelming bitterness and mineral aftertaste that made it unsuitable for brewing coffee. Evian’s high mineral content, particularly its high levels of calcium and bicarbonates, likely caused the coffee to over-extract, drawing out too much bitterness and masking the more subtle flavours. Alternatively, it could be said that the higher mineral content translated into a cup that was unpleasant (for me, this bean, water temperature, 93 degrees Celsius, and brewing method).
Why Mineral Content Matters for Coffee
Water is a crucial part of coffee brewing, and its mineral content can make or break the flavour of your brew. As demonstrated here, waters with varying calcium, magnesium, and bicarbonate levels produced noticeably different flavour profiles. It is said that:
Calcium helps extract the right compounds, giving the coffee more body and mouthfeel.
Magnesium brings out sweetness and contributes to the clean taste in lighter roasted coffees.
Bicarbonates neutralise acidity and can dull bright, fruity flavours if present in excess.
The Specialty Coffee Association recommends that water used for brewing coffee should have a balanced mineral content to avoid either under-extraction (which can lead to sour or weak coffee) or over-extraction (which leads to bitter, flat coffee). Finding the right balance of minerals can help unlock the full potential of your coffee, highlighting its acidity, sweetness, and body in a harmonious way.
Conclusion
Through this experiment, Voss water emerged as the best option for brewing Kelloo coffee, delivering a balanced and mild flavour profile with subtle sweetness. If you're looking to brew a bright, floral, and balanced cup of coffee, in this case, choosing water with low mineral content, especially in bicarbonates, seems to provide the best results. On the other hand, waters high in bicarbonates or with imbalanced mineral content can lead to bitterness, dryness, or over-extraction.
There may be more bottled waters I could add to this list; these were toward the upper-end of the price range at the supermarket and they provided a range of mineral content to test. It might be there is a cheaper option that does just as well as Voss and Royal Deeside, which of course would be advantageous.
As with many variables in coffee brewing, water plays a key role in shaping the final flavour. So next time you brew your favourite coffee, think about the water you use—it might just be the difference between a good cup and an exceptional one.
