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The secret to the perfect cup of coffee revealed

... and it's all in the hardness of the water

Scientists have cracked the secret behind what most cafés have been claiming to have for years – the perfect cup of coffee. And the secret ingredient is surprisingly simple.

As it turns out, the key to good cup depends on the hardness of the water used.

Experts used compositional chemistry methods to examine the impact of different kinds of water on the flavour of coffee to find that reasonably hard water had the best results.

Findings in a new paper show that it made a “dramatic difference” to the quality of coffee. And while high bicarbonate levels were bad for flavour, high magnesium ion levels were found to increase the extraction of coffee into water.

According to Christopher Hendon, chemist at the University of Bath, sodium-rich water – such as that produced from water softeners - didn’t release the flavour’s full potential.

Hendon, who along with UK Barista Champion Maxwell Colonna-Dashwood is preparing to represent the UK in the World Barista Championships in Italy, said: “Coffee beans contain hundreds of chemicals; the precise composition depends on the type of bean and how it is roasted.

”The flavour of the resulting coffee is determined by how much of these chemicals are extracted by the water, which is influenced by roast profile, grind, temperature, pressure and brew time.

“We've found that the water composition is key to the proportions of sugars, starches, bases and acids extracted from a particular roast.”

Mr Colonna-Dashwood, who owns Colonna and Small's coffee shop in Bath and is a co-author on the paper, said starting with a “reasonably hard” tap water achieved the best results.

But taste perfection might not be top of everyone’s agenda, he added: “Traditionally the coffee-making industry is most concerned about using water that doesn't scale up their machines.”