The perfect cup of coffee! Grinding fewer, coarser beans creates a cheaper, more consistent and stronger cup of espresso, researchers discover

  • Experts in mathamatics, physics and material science worked on the problem
  • The international team used a mixture of experiments and computer modelling 
  • Baristas traditional use lots of finely ground beans to create the ‘espresso taste’
  • Researchers say you can get the same taste but more consistently across drinks by using few, more coarsely ground coffee beans 

Grinding fewer coffee beans more coarsely creates a cheaper, consistent and stronger cup of espresso, an international team of researchers discover. 

Experts in maths, physics and material science from the USA, UK and Switzerland set their mind to improving the world’s most popular drink.

Currently baristas use lots of finely ground beans to get a mix of bitterness and sour acidity but it is ‘unpredictable and nor reproducible’, say researchers. 

Computer models and experiments revealed that ‘just using less coffee and grinding it more coarsely’ gives the same taste but more consistently across multiple brews.

The team say the drop in the number of required beans could have another impact – in saving the US coffee industry alone up to  £850 million per year.

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A cup of espresso showing beans in the background. Researchers created a new mathematical model to predict the perfect recipe for an espresso 

Mathematician Jamie Foster launched the study after finding that sometimes two shots of espresso, made in seemingly the same way, can sometimes taste different. 

A cup of coffee is composed of over 1,800 chemical components and estimates put the number of cups of drunk globally at more than a couple of billion each day.

The norm for brewing an espresso shot is to grind a relatively large amount of coffee beans, just under an ounce, as finely as possible.

Researchers say that should be cut by a quarter to create the same high quality cup as traditional methods, but cheaper and with a more consistent flavour. 

The fine grind, common sense goes, means more surface area exposed to the brewing liquid, in turn boosting extraction yield – but the team found that a fraction of the ground coffee that actually dissolves ends up in the final drink.

So the researchers put together a mathematical model to explain the extraction yield based on the factors under a barista’s control.

These include options such as the masses of water and dry coffee, the fineness or coarseness of the grounds, and the water pressure.

The study found that grinding as finely as the industry standard clogged the coffee bed and actually reduced the extraction yield.

This resulted in wasted raw materials and introduced variation in taste by sampling some grounds and missing others entirely.

After making thousands of shots of coffee and ‘crunhing the numbers’ the team, including researchers from The University of Oregan, created the ‘perfect recipe’.

It simultaneously maximises extraction and produces espresso that would taste similar from one cup to the next, says lead author Christopher Hendon.

‘One way to optimise extraction and achieve reproducibility is to grind coarser and use a little less water, while another is to simply reduce the mass of coffee.’

Developing a model representative of espresso brewing was not a straightforward task, according to co-author Jamie Foster from the University of Portsmouth.

‘You would need more computing power than Google has to accurately solve the physics and transport equations of brewing on a geometry as intricate as a coffee bed’, the researcher said.

To get past this hurdle they used a technique called electrochemistry – likening how caffeine and other molecules dissolve out of coffee grounds to how lithium ions move through the electrodes of a battery.

Close-up of espresso pouring from coffee machine. Professional coffee brewing; Shutterstock ID 278456510; Purchase Order: –

This led to a rigorous coffee extraction model capable of making powerful and testable predictions.

They say this simple discovery will save cafes and the coffee industry a fortune due to requiring fewer beans per cup.

At the current price of roasted coffee beans, dropping the mass of dry coffee from 20 to 15 grams per drink would add up to savings of a few thousand dollars per year for a small cafe, and $1.1 billion to the whole US coffee industry, they claim.

‘Being more efficient with coffee bean usage would also reduce waste at a time when supply is under threat from changing climate in key production areas.’

But the researchers stress their results do not purport to reduce all of espresso making down to a single set of brewing conditions or to a lone flavour profile.

‘Though there are clear strategies to reduce waste and improve reproducibility, there is no obvious optimal espresso point’, said Dr Hendon.

‘There is a tremendous dependency on the preferences of the person producing the coffee; we are elucidating the variables that they need to consider if they want to better navigate the parameter space of brewing espresso.’

A spokeswoman for the University of Portsmouth said the new technique was trialled in a small US coffee shop over a year and they found they were saving thousands of dollars with no change in taste.

‘The research has been published in the journal Matter. 

HOW CAN YOU MAKE THE PERFECT CUP OF COFFEE EVERY TIME?

An assistant chemistry professor of chemistry from the University of Oregon called Dr Christopher Hendon used science to find out how to make the perfect cup of coffee every time. 

Known as ‘Dr Coffee’ in certain social circles, the caffeine-loving scholar looked at how certain things can affect the taste of coffee. 

1. Use hard water 

He found that hardness of water is related to better taste, the harder the water the stronger the taste.

Hard water is created by the presence of magnesium and calcium. 

These impurities help caffeine adhere better, which improves the taste and quality of the drink. 

2. Store the coffee beans in the fridge 

The research also revealed that the storage of coffee beans was very important for taste.

Fresh beans stored in the fridge came out on top here because freshly roasted coffee contains carbon dioxide that easily evaporates. 

As this evaporates, so does most of the flavour. 

3. Choose your grinder carefully  

The type of grinder used is also important, as if the beans are ground up too finely they can clump together, detracting from the flavour. 

A powder is desirable as it increases surface area, which in theory creates more flavour. 

This is a fine balance however, as ground too fine the coffee will become clumpy – detracting from the overall experience. 

4. Mix the coffee and the water evenly  

The final key to a good cup of coffee is the way the hot water mixes with the coffee.

This process should be consistent and steady for maximum taste.  

 

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