Coffee aficionados insist that the perfect espresso requires finely ground beans, tamped down tightly, to let steaming water pass through and create the fullest flavour.

But according to scientists baristas are getting it wrong, and could save time, money and improve taste by using courser grounds, which allow the water to flow more freely.

The problem, according to mathematicians at the University of Portsmouth and the University of Oregon, lies in the fact that grounds are often packed so tightly that they form clumps which water cannot pass through.

The teams performed mathematical modeling and brewed hundreds of espresso shots to discover the key variables required to make consistently tasty coffee.

They concluded that using 15 grams of coffee rather than 20, at a coarser grind, and letting the water run for just seven to 14 seconds, instead of the usual 25, gives the best flavour, and prevents any bitterness from occurring.

They calculated that the new method, reduces the amount of coffee used in espresso by 25 percent, and would save coffee shops 10p per drink.

Dr Jamie Foster, of the University of Portsmouth said: “The conventional wisdom is that if you want a stronger cup of coffee, you should grind your coffee finer. This makes sense because the finer the grounds mean that more surface area of coffee bean is exposed to water, which should mean a stronger coffee.