Extracting the best flavor from coffee

Date:
May 9, 2023
Source:
American Institute of Physics
Summary:
Researchers explore the role of uneven coffee extraction using
a simple mathematical model. They split the coffee into two
regions to examine whether uneven flow does in fact make weaker
espresso. One of the regions in the model system hosted more
tightly packed coffee than the other, which caused an initial
disparity in flow resistance. The extraction of coffee decreased
the flow resistance further. Understanding the origin of uneven
extraction and avoiding or preventing it could enable better brews
and substantial financial savings by using coffee more efficiently.


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FULL STORY ========================================================================== Espresso coffee is brewed by first grinding roasted coffee beans into
grains.

Hot water then forces its way through a bed of coffee grains at high
pressure, and the soluble content of the coffee grains dissolves into
the water (extraction) to produce espresso.

In 2020, researchers found that more finely ground coffee beans brew a
weaker espresso. This counterintuitive experimental result makes sense if,
for some reason, regions exist within the coffee bed where less or even
no coffee is extracted. This uneven extraction becomes more pronounced
when coffee is ground more finely.

In Physics of Fluids, from AIP Publishing, University of Huddersfield researchers explored the role of uneven coffee extraction using a simple mathematical model. They split the coffee into two regions to examine
whether uneven flow does in fact make weaker espresso.

One of the regions in the model system hosted more tightly packed coffee
than the other, which caused an initial disparity in flow resistance
because water flows more quickly through more tightly packed grains. The extraction of coffee decreased the flow resistance further, as coffee
grains lose about 20% to 25% of their mass during the process.

"Our model shows that flow and extraction widened the initial disparity
in flow between the two regions due to a positive feedback loop, in which
more flow leads to more extraction, which in turn reduces resistance and
leads to more flow," said co-author William Lee. "This effect appears
to always be active, and it isn't until one of the regions has all of
its soluble coffee extracted that we see the experimentally observed
decrease in extraction with decreasing grind size." The researchers
were surprised to find the model always predicts uneven flow across
different parts of the coffee bed.

"This is important because the taste of the coffee depends on the level
of extraction," said Lee. "Too little extraction and the taste of the
coffee is what experts call 'underdeveloped,' or as I describe it: smoky
water. Too much extraction and the coffee tastes very bitter. These
results suggest that even if it looks like the overall extraction is
at the right level, it might be due to a mixture of underdeveloped and
bitter coffee." Understanding the origin of uneven extraction and
avoiding or preventing it could enable better brews and substantial
financial savings by using coffee more efficiently.

"Our next step is to make the model more realistic to see if we can obtain
more detailed insights into this confusing phenomenon," said Lee. "Once
this is achieved, we can start to think about whether it is possible to
make changes to the way espresso coffee is brewed to reduce the amount
of uneven extraction."
* RELATED_TOPICS
o Health_&_Medicine
# Staying_Healthy # Diseases_and_Conditions
o Matter_&_Energy
# Nature_of_Water # Nuclear_Energy
o Computers_&_Math
# Computer_Modeling # Mathematical_Modeling # Mathematics
* RELATED_TERMS
o Coffee o Caffeine o Constructal_theory o Turbulence
o Aerodynamics o Viscosity o Extraction_(dental) o
Psychoactive_drug

========================================================================== Story Source: Materials provided by American_Institute_of_Physics. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. William Lee, Ann Smith, Arsalaan Arshad. Uneven Extraction in Coffee
Brewing. Physics of Fluids, 2023; DOI: 10.1063/5.0138998 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230509122007.htm

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