Baristas are brewing it all wrong, claim scientists

COFFEE aficionados insist that the perfect espresso requires finely ground beans, tamped down tightly so that steaming water can pass through and create the fullest flavour.

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

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

They used theoretical modelling and brewed hundreds of espresso shots to discover the key variables required to make a consistently tasty brew.

Using 15 grams of coffee rather than 20, at a coarser grind, and letting the water run for just 7-14 seconds, instead of the usual 25, gave the best flavour and prevented any bitterness from occurring, they said.

Their method also reduced the amount of coffee used by 25 per cent and could save cafés 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.

“When beans were ground finely, the particles were so small that in some regions of the bed they clogged up the space where the water should be flowing.

“These clogged sections of the bed are wasted because the water cannot flow through them and access that tasty coffee that you want in your cup. If we grind a bit coarser, we can access the whole bed and have a more efficient extraction.”

For people brewing at home the perfect coarseness would be difficult to judge with the naked eye, he said, but he recommended using a quarter less coffee than usual and carrying out triala-nd-error taste tests.

Researchers trialled the new method in a small US coffee shop over a period of a year and reported saving thousands of dollars.

Dr Christopher Hendon, a chemist at the University of Oregon, said: “If you use 15 grams instead of 20 grams of coffee and grind your beans coarser, you end up with a shot that runs really fast but tastes great.

“You end up extracting more positive flavours from the beans, so the strength of the cup is not dramatically reduced. Bitter, off-tasting flavours never have a chance to make their way into the cup.”

He added: “For the local shop owner, this is an opportunity to save a lot of money without sacrificing quality.

“For the producer, this should encourage them to continue to produce highquality coffee that can earn them the most money, knowing that more people will have access to it.”

While previous studies have looked at drip filter coffee, this is the first time mathematicians have used modelling to examine the science of the espresso.

The study was published in the journal Matter.