mineral content of water for coffee

How does the mineral content of water affect espresso?

Imogen Rose Phillips speaks with Water for Coffee author, Maxwell Colonna-Dashwood, and national sales manager at BWT, William Hinton, to analyse the relationship between water’s mineral content and the quality of espresso.

In the world of specialty coffee, a lot of noise is often made about water. The line about a cup of coffee being “98% water” is frequently bandied around, while the debate around the “perfect temperature” has raged for years.

But when discussing water, an often overlooked factor is its chemical composition or, more specifically, its mineral content.

Water comprises many more compounds than just H20, including dissolved ions of metals like magnesium, calcium, and iron. These minerals have the ability to affect the near 1,500 flavour compounds found in coffee in various ways.

In fact, the bond between hydrogen and oxygen is quite weak, which is why compounds like bicarbonates are so frequently found in water. The concentration of bicarbonates dictates the alkalinity of water, with “hard water” having high mineral content, and “soft water” being more acidic.

There’s a sweet spot between the two extremes, and the generally accepted pH for drinking water is around seven, which is exactly halfway between alkaline and acidic. Furthermore, minerality of 50mg/L to 157mg/L is considered perfect.

Maxwell Colonna-Dashwood is a barista champion, roaster, café owner, and the author of the pioneering Water For Coffee. He explains that bicarbonate is the most important factor when it comes to how water affects cup quality.

“It’s going to control acidity, so it’s why someone in a hard water area will find their coffee tastes flat. Equally, you don’t want ‘none’ of it, because soft water coffee can be very acidic.”

How do these minerals affect espresso?

A chemical reaction occurs when espresso is extracted. Depending on the coffee’s solubility, varying levels of its aromatic compounds are infused into water. The quantity and composition of this water will affect the sugars, starches, and acids that ultimately end up in the cup.

Theoretically, the mineral makeup of water affects espresso less than it does filter coffee, simply because of the different infusion times involved.

“Effectively, espresso is a concentrate, so it’s a lot more coffee to a lot less water,” Maxwell explains. “It may sound obvious, but if you only use 50ml water, that’s not as many minerals, is it?”

As such, water composition should be monitored and tweaked depending on the specific coffee being brewed. It’s simply another in the long list of variables that affect coffee extraction, like grind size or roast level.

“If you’re using a weaker ratio, like filter coffee, you’d want a softer water,” Maxwell elaborates. “For espresso, slightly higher bicarbonate is desirable.”

The only problem, he notes, is that too much hardness results in scale buildup in your espresso machine. “What’s best for a hassle-free machine isn’t necessarily what’s best for cup quality,” he says.

Modern espresso machines like the Carimali SilverAce and Elektra Kup are fully capable of self-descaling, solving this issue. Furthermore, they can automatically adjust brewing variables according to the water hardness level set by the user.

Maxwell adds that other minerals of note are calcium and magnesium, which seem to have an impact on the cup profile.

“If you’ve got some of them, you’ve got a bigger, fruitier cup,” he adds. “But the science is a little bit inconclusive. So they seem to have an impact, but not as big as bicarbonates.”

Ultimately, these effects are governed by subjective tastes. Whoever’s brewing the coffee will need to play around with water and decide what works for them.

“There is no such thing as the perfect water,” Maxwell says. “I think it would be easier if there was, because then we’d all work towards that.”

How to maintain consistent mineral content?

Aside from bottled water and tap water, there are other ways to source the water that works best for brewing espresso.

According to the SCA, the ideal mineral content in water for coffee is a pH of 7.0 with no odour or colour, zero chlorine, alkalinity of 40ppm, and calcium hardness of 50-175ppm CaCO3. In simpler terms, the water must be clean and low in sodium and chlorine.

In William’s case, BWT, which supplies the water for the World Barista Championships, is able to ask its clients exactly what they want from their water and can deliver a product with precisely-adjusted mineral content.

As well as useful reverse osmosis and remineralisation technology, BWT has developed a dedicated home-use range. These include mineral cartridges, jug filter systems, and in-line filters that can be installed under the sink.

For home baristas, however, William suggests consulting an objective, reliable advisor who can give “chemically accurate advice”.

Maxwell controls his use of water by tasting his coffees with several different waters. This way, he can achieve some level of consistency, which is what any brewer is looking for.

“The key to consistency is to test your water,” he explains. “Even if you do the research and set it up, it’s important not to forget about it. Whenever something changes in the café, the first thing I think about is whether something’s changed in the water.”

However, he says that consumers and businesses do have several options when it comes to sourcing water.

“If you want to make your own water, you can buy distilled water and add in salts,” he suggests. “Bottled water is one option, but it’s just so wasteful with the plastic and expensive. Ion exchange cartridges and reverse osmosis can do a really good job.”

Ultimately, he concludes that businesses and home consumers should speak to their roasters for advice.

“That’s the shortest cut for a home brewer, especially if they’re near you, because then they’re using the same water as you,” he adds.

How does the mineral content of water affect espresso?

Related Articles