Why Coffee Tastes Different in Cape Town

I just spent a week in Cape Town and just like every previous visit, I try out artisanal roasters in my quest to find great coffee. But, just like every previous visit, I leave disappointed and unable to find a cup of coffee that wasn’t somewhat acidic in taste. For some time now I have blamed these artisanal roasters for their light roasts or their baristas for over extraction, and don’t get me wrong, I like acidity in my espresso, but there is a limit. So this time I packed in my water test kit because we have started a water filter division at Famous Brands Coffee Company, and while setting that up, I have been educated on the wonders of water chemistry and just how critical “good” water is in making great coffee. More about what I found a little later. It really shouldn’t be so surprising really because water makes up about 98% of a cup of coffee and so water quality, just like coffee bean quality, should be important to a barista and to every consumer of coffee. We talk about this in our article on why coffee machines need water filters. Yet, whenever I asked a barista or café owner about the quality of their water, I got a blank look and a reference to the fact that they had a water filter fitted. That would have been my understanding a year ago – fit a filter and you are good to go. So I wasn’t surprised, nor judgemental. It just made me realise how little attention is given to the water component by coffee professionals. Just like not all water is the same, neither are water filters. Water filters can be used for many reasons such as to:

1. filter out unwanted particles like rust, algae, sand etc and even remove bacteria and cysts using extremely fine membranes; and/or
2. remove chlorine taste and odour and heavy metals; and/or
3. either remove calcium ions through ion exchange, or soften water with silicon phosphate to prevent calcium carbonate adherence to metal surfaces; and/or
4. completely remove all ions, bacteria and some viruses if configured as a reverse osmosis system.

The question is, what exactly does your water contain and what do you want to keep and what do you want to remove with a water filter to end up with great coffee? You want three things to be in the right range in your water if your coffee is going to taste good (and this comes from the Specialty Coffee Association itself!):

1. Hardness, or the concentration of calcium and magnesium ions must be within a range of 50 to 100 ppm for the best espresso. If your water is too hard, say 100 ppm upwards, you’ll get over extraction and if it is too soft, you’ll get under extraction and a much reduced flavour profile. Studies have shown that at 20 ppm hardness only 1/3^rd of the Furnaeol, a key flavour compound, is extracted compared to water with a 60 ppm hardness. Not great for taste!
2. Carbonate and bicarbonate concentration, often referred to as alkalinity, must be between 40 and 70 ppm. These compounds act as a pH buffer and so stabilise pH in the face of increasing or decreasing acidity. Coffee is full of acids like chlorogenic, quinic, citric, acetic, lactic, malic, phosphoric, linoleic, and palmitic acid, so if your water is low in these buffering compounds, you can expect increased acidity on extraction.
3. Finally pH, which is an indicator of how acidic or alkaline your water is, needs to be withing a range of 7-8.5 to ensure extraction is optimal. As pH increases, so does extraction of flavour compounds.

So what does this all mean for the flavour of coffee in Cape Town? Quite tellingly, the tap water samples in Sea Point had a hardness of 71 ppm, an alkalinity of only 18 ppm, and a pH of 8.5. In Franschhoek, hardness and alkalinity were both just 17.9 ppm and pH was just 6.54. What this means is that coffee in Cape Town would have normal flavour extraction but tend towards being overly acidic as the pH buffering capacity of the water is low. The pH of 8.5 would help to mitigate some of the excess acidity, but light roasted coffee would still come across with excess acidity. The situation in Franschhoek is even worse with tap water having a very low hardness leading to under extraction of flavour. An acidic pH without any real buffering capability results in a notable increase in the acidity of the coffee. Here, there is a need to use bottled water that has been sourced with hardness, alkalinity and pH in range. So is it surprising that I find the coffee in the Cape region to be more acidic than in Gauteng. Not at all.

Plan your next brew

Water quality varies by location and over time. Follow your brewer manufacturer’s guidance when selecting water or filtration, and seek advice from a qualified water-treatment supplier where needed.

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