beanscenemag.com.au beanscenemag.com.au 8383Barista Hustle, then refined by a process
engineer via TheDIYCoffeeGuy.com,
a brew water temperature of 93°C
can result in an effective 87°C or even
82.5°C extraction temperature (for
grinds at 50°C and 20°C respectively).
You are probably brewing espresso a lot
cooler than you imagined.
Extraction temperature plays an
all-important part in shaping the flavour
profile of the final beverage.
The solubility of all constituents
of the coffee bean changes with
temperature. Flavour molecules become
more soluble as the heat increases,
but they do so at different rates, which
affects their ratio in the final brew.
As an example, the solubility of
sugars is roughly 2.5 times higher in
boiling water than at room temperature.
No wonder that higher brew
temperatures favour the extraction of
sugars, as backed by TR Lingle’s
The Coffee Brewing Handbook. The
handbook also points out that the
concentration of acids remained similar
between 74°C to 100°C. Caffeine
concentration wasn’t found to change
much either in the temperature range
used for espresso brewing (which is also
in agreement with my investigations
as published in BeanScene’s
February 2019 issue).Other researchers investigated
the concentration of compounds
responsible for fruity flavours and found
that these were extracted at higher
rates when the brew water temperature
was set to 92°C compared to 88°C. At
96°C and above, there was an increased
concentration of bitter flavours due to
the breakdown of chlorogenic acids at
such high temperatures.
When I put espressos made with
brew water at 90°C, 92.5°C and 95°C
to a panel of judges, the sample at
92.5°C was found to be the most
balanced. Of course, the tastiest
combination of extracted flavours will
strongly depend on the coffee you are
using. As a guideline, we can expect
lower temperatures to result in more
prominent acidity and less bitterness,
but also less body and sweetness.
Higher temperatures can help increase
body and sweetness, at the cost of
introducing more bitterness and
slightly reducing acidity.
Higher extraction temperature also
means that carbon dioxide gas in the
puck will be present at higher pressure,
meaning a higher resistance, which
will somewhat counteract the observed
“speeding up” of hotter shots.
Lastly, the taste experience strongly
depends on the temperature wetaste the coffee at. A study published
in the prestigious science journal
Nature in 2005 found that tiny
microscopic channels in our tastebuds
are responsible for changing taste
perception at different temperatures.
These channels send stronger electrical
signals to the brain when food is
tasted at higher temperatures.
When we taste coffee hotter,
its sweetness and, in particular, its
bitterness will become more prominent.
As such, keeping your cups at a steady
temperature helps deliver more
consistent coffee to the customer.
If you’re adding milk, remember
that not only its temperature but
also its volume will affect the final
drinking temperature, along with
the temperature of your dine-in
or takeaway cups.
Take another look at the map of
temperature dependent variables.
Whether your grinder and machine are
just warming up during the day or you
have decided to adjust the temperature
of the brew water, the consequences are
far-reaching.
When optimising extraction
temperature, my one piece of advice is
to remain patient: the sheer bulk of the
machine means that changes will need
some time to take effect.Image 1: This illustration highlights that virtually all
components of a coffee machine and grinder impact
temperature (T) and flavour profiles.beanscenemag.com.au 83Barista Hustle, then refined by a process
engineer via TheDIYCoffeeGuy.com,
a brew water temperature of 93°C
can result in an effective 87°C or even
82.5°C extraction temperature (for
grinds at 50°C and 20°C respectively).
You are probably brewing espresso a lot
cooler than you imagined.
Extraction temperature plays an
all-important part in shaping the flavour
profile of the final beverage.
The solubility of all constituents
of the coffee bean changes with
temperature. Flavour molecules become
more soluble as the heat increases,
but they do so at different rates, which
affects their ratio in the final brew.
As an example, the solubility of
sugars is roughly 2.5 times higher in
boiling water than at room temperature.
No wonder that higher brew
temperatures favour the extraction of
sugars, as backed by TR Lingle’s
The Coffee Brewing Handbook. The
handbook also points out that the
concentration of acids remained similar
between 74°C to 100°C. Caffeine
concentration wasn’t found to change
much either in the temperature range
used for espresso brewing (which is also
in agreement with my investigations
as published in BeanScene’s
February 2019 issue).
Other researchers investigated
the concentration of compounds
responsible for fruity flavours and found
that these were extracted at higher
rates when the brew water temperature
was set to 92°C compared to 88°C. At
96°C and above, there was an increased
concentration of bitter flavours due to
the breakdown of chlorogenic acids at
such high temperatures.
When I put espressos made with
brew water at 90°C, 92.5°C and 95°C
to a panel of judges, the sample at
92.5°C was found to be the most
balanced. Of course, the tastiest
combination of extracted flavours will
strongly depend on the coffee you are
using. As a guideline, we can expect
lower temperatures to result in more
prominent acidity and less bitterness,
but also less body and sweetness.
Higher temperatures can help increase
body and sweetness, at the cost of
introducing more bitterness and
slightly reducing acidity.
Higher extraction temperature also
means that carbon dioxide gas in the
puck will be present at higher pressure,
meaning a higher resistance, which
will somewhat counteract the observed
“speeding up” of hotter shots.
Lastly, the taste experience strongly
depends on the temperature wetaste the coffee at. A study published
in the prestigious science journal
Nature in 2005 found that tiny
microscopic channels in our tastebuds
are responsible for changing taste
perception at different temperatures.
These channels send stronger electrical
signals to the brain when food is
tasted at higher temperatures.
When we taste coffee hotter,
its sweetness and, in particular, its
bitterness will become more prominent.
As such, keeping your cups at a steady
temperature helps deliver more
consistent coffee to the customer.
If you’re adding milk, remember
that not only its temperature but
also its volume will affect the final
drinking temperature, along with
the temperature of your dine-in
or takeaway cups.
Take another look at the map of
temperature dependent variables.
Whether your grinder and machine are
just warming up during the day or you
have decided to adjust the temperature
of the brew water, the consequences are
far-reaching.
When optimising extraction
temperature, my one piece of advice is
to remain patient: the sheer bulk of the
machine means that changes will need
some time to take effect.Image1: Thisillustrationhighlightsthatvirtuallyall
componentsofa coffeemachineandgrinderimpact
temperature (T) andflavourprofiles.