MAKING COFFEE,
NO MISTAKE.
Science in the neighborhood: How to make really
good coffee
By Summer
Ash | Mar 8, 2011
Sitting at the end of
the long wooden bar, I watch with curiosity
as Richie begins his pour. He starts the
stopwatch on his cell phone and proceeds to
pour steaming hot water over the coffee
grounds in a precise choreographed motion.
The water hits the grounds and starts to seep
through while small bubbles rise up to form a
layer of foam in its place. Richie adds the
water in successive streams spiraling outward
from the center of the grounds, an ounce at a
time. The water level rises and then falls.
At 2 minutes and 31.48 seconds, there is a
mound of dissolved grounds left in the filter
and a rich, caramel-colored liquid fills the
glass below. For the first time in my life, I
find myself eager to taste a cup of plain
coffee.
Rich Nieto, or Richie as I know him, is a
co-owner of my local coffee bar, Sweetleaf,
which is a stones throw from my
apartment in Queens. Since its opening in the
spring of 2008, Sweetleaf has become a staple
both in the neighborhood and in my daily life.
I stop in each morning for a mocha to satisfy
my sweet tooth and for a chat with the
baristas who have come to know me as their
local astrophysicist. Most of the
time, we engage in small talk about the day
ahead, the weather, or the weekend, but
occasionally the conversations wander deeper
into what Im teaching, what
theyre reading, or whats new in
the neighborhood. With Richie, these
conversations often veer into science.
When Richie decided to open Sweetleaf, he
knew very little about the world of specialty
coffee. But he threw himself into learning
all there was to know about its production
and consumption. He identified the variables
he had to play with as a barista and started
experimenting. On more than one occasion,
Ive stopped in to find Richie enlisting
the staff and even a customer or two in blind
and double blind taste tests as he played
with the settings on the coffee machines. His
co-owner, Alfred Arundel tells me, "Richie
has always been like this, hell spend
hours just studying one thing, thinking about
what the variables are and how they interact."
His systematic approach impresses me, and
weve often discussed the importance of
th scientific method. While Ive never
stopped to think about the variables he is
working with, his baristas are all too
familiar with his tinkering. Georgia Sanford
has been working in coffee shops most of her
life, but was only ever trained to get the
same tasting product each time, and not to
question whether the taste itself could be
better. "Richie started asking why not
play with the process and see what happens to
the taste? Now not only are all our baristas
trained to consistently deliver the best
tasting results, but we understand more about
the variables and how they affect the outcome."
It was a slow Wednesday afternoon when I
discovered three electronic scales sitting
neatly in a row at the end of the bar. Seeing
my curiosity, Richie walked over to explain
they were for a new drink he wanted to offer
called a "pour over." Essentially a
single serving of coffee brewed to order, a
pour over is the coffee worlds return
to basics.
Coffee trees grow primarily in a belt
around the equator in remote regions at
moderate altitudes with mild climates. The
beans themselves are actually the seeds
inside the fruit of the coffee tree, known as
the cherry. Unfortunately, coffee
cherries dont all ripen at the same
time between trees or even between branches.
They must be individually inspected and hand-picked.
The cherries are put then through one of two
processes, dry versus wet, to separate the
beans from the pulp of the fruit. Once dry,
the last protective layer around the bean,
the husk, is removed and the beans are sorted,
packaged, and shipped to commercial customers
around the world. Upon reaching local
distributors, the beans are then roasted and
delivered to retail clients such as coffee
bars and cafes where they are finally
transformed into your beverage of choice.
Coffee drinks generally take two forms:
espresso based or brewed. A shot of espresso
is pulled by forcing hot water
through coffee grounds at 135 pounds per
square inch. From beginning to end, water is
in contact with the grounds for all of 30
seconds. Contrast this with brewed coffee,
which requires upwards of five minutes
depending on the number of cups being brewed
at a time. The grounds are poured into a
filter and the requisite amount of water is
added. Then you wait. Drip by drip the water
makes its way through the grounds under the
force of gravity alone, dissolving the
grounds in its path. Cafes tend to brew up to
a dozen cups at a time in advance so they add
a large amount of water all at once to use
the weight of the water to speed the process.
However, neither of these methods allow the
barista full control over the extraction
process.
Extraction is the process of dissolving
the coffee grounds in water. When the water
hits the grounds, acids are the first
chemical components to be dissolved, then
sugars and finally, the bitter components.
The more grounds that dissolve, the higher
the extraction. But more is not
necessarily better. Too much and the bitter
flavor is overwhelming; too little and the
coffee is on the sour side. But in between 19%-22%
is the sweet spot
literally. Proper extraction brings out
complexities within a coffee that are
imparted during its production but often get
lost in more commercial consumption. The
percent extraction for a given cup of coffee
can vary based on several factors, the most
important of which are: the size of the
grounds, the time that the water is in
contact with the grounds, and the
distribution of the water among the grounds.
Brewed coffee is often characterized by
uneven extraction. The automated system of
passing water through a conical mound of
coffee grounds inhibits even extraction. The
grounds in the center get doused with the
most water and as a result, the coffee from
these grounds is over- extracted. Other
grounds around the perimeter barely interact
with the water at all producing coffee that
is under-extracted. And unfortunately the law
of averages is no help as the average
extraction is often dragged upwards towards
22% into borderline bitter territory.
Espresso, by contrast, is the product of
even extraction, but comes with its own
concessions. While not automated, the process
of pulling a shot of espresso is extremely
standardized with little room for variation.
In order to have repeatable success (i.e., a
consistent product), the grounds must be
finer and made up of a blend of beans. The
espresso grind size allows water to come into
contact with more of the grounds as it is
forced through them at high pressure. If the
grounds were larger, the water would pass
straight through without barely any
extraction. Smaller, and more pressure would
be required to extract anything at all. A
blend of beans is used to defend against
noticeable differences in an individual
coffee harvest from year to year.
With the pour over, the barista can now
control all aspects of the extraction process;
the precise timing and distribution of the
water can ensure that the grounds are evenly
extracted in both time and space. The set up
is roughly the same as any filter or drip
coffee machine; the difference lies in scale
and technique.
At the end of the bar, I watch as Richie
measures out 21 grams of coffee beans from a
Colombian roast. He puts the beans in the
grinder and adjusts the knob to set the grind
size. With the touch of a button, the machine
whirls to life and the beans are transformed
into a coarse powder. Richie transfers the
coffee to an inverted conical ceramic cup
that sits atop a glass receptacle on one of
the scales. The cup has a nickel-sized hole
in the bottom and is lined with custom-sized
filter, which Richie has dampened with water
so that the filter sticks to the wall of the
cup. He fills a small kettle with twelve
ounces of hot water and tilts it over the
coffee grounds.
As he pours the water, he explains that he
is pre-wetting the grounds, "The point
of the pre-wet is to get the coffee ready to
receive the water. Theres a lot of
carbon dioxide trapped in the grounds so we
have to de-gas them first." As the hot
water hits the grounds, it forms a layer on
the surface before it starts to drop and seep
through them. He gives the grounds a stir to
wet them evenly and the water begins to
bubble and foam as more and more carbon
dioxide is released.
When the water level drops to just about
level with the grounds, Richie picks up the
kettle again and starts his stopwatch. This
time he adds a couple of ounces of water to
soak the coffee again and then he begins his
pour.
"I'm going to work in a circular
motion, starting from the center and making
bigger and bigger circles around it. By doing
this, I'm controlling a few different things.
One, I'm controlling the time of the
extraction [the time that the water is in
contact with the grinds]. And two, Im
controlling the distribution of the water. If
I fill the water all the way up, I can speed
it [the extraction process] up. If I only put
a little bit [of water in], I can slow it
down. What I don't want is for the water to
drop below the coffee because any coffee that's
not touching water is not extracting."
Richie adds two ounces at a time, each one
in an expanding spiral pattern. Gravity draws
the water down through the grounds,
dissolving them along the way, and drawing
their rich flavor out and into the glass
below. After the third spiral pour, he puts
the kettle down and picks up a teaspoon. He
gives the mixture a stir, creating a small
vortex. "This little whirlpool here is
going to keep the coffee grounds in the
center and off of the side of the walls. The
most important part about the brewing process
is that all the grounds be in contact with
the water," he explains.
The stopwatch is still running,
approaching two minutes and thirty seconds,
Richies target time for the water to
have completely filtered through the grounds
and into the cup below. At only 1.48 seconds
past his mark, the last of the water flows
down into the glass below leaving behind a
small, porous dome of dissolved grounds.
Richie can tell when hes between 19-20%
extraction now by taste alone, but when he
was learning he had to rely on data
scientific data. He bought a refractometer to
measure the total amount of dissolved solids
in the resulting cup of coffee and he has a
program that can translate this number into
the percent extraction. He spent well over
fifty hours perfecting his technique, but
through research, conversations with other
baristas, and experimentation, he began
hitting the sweet spot again and again. As
Richie says, "When you're converting
coffee beans into a cup of coffee, you can
play a major role in what that ends up
tasting like."
As a novice with a sweet tooth, Ive
never strayed from my preferred mocha,
fearing the bitter taste I associate with
straight coffee. I admit that impression is
at least a decade old and I cant recall
the last time I gave coffee a chance. So
after witnessing my first pour over, I was
eager to taste coffee again for the first
time. The sweetness hit me immediately and
the subtle layers of caramel were immediately
apparent. It was so smooth and rich and
complex. As clichéd as it sounds, Id
never experienced anything like it. The pour
over is a drink that tells a story. It
captures all that the beans have seen and
reveals how each part of the process has left
its fingerprint. After tasting my first pour-over,
my mocha tasted like a chocolate milkshake.
Image:
Coffee Pour Over, by Kate.moon at Wikia
Coffe Wiki
About
the Author: Summer Ash is currently
a postdoc at Columbia University in the
Astronomy & Astrophysics Department and
an instructor for Frontiers of Science in the
Core Curriculum. Her doctoral research was on
the evolution of radio galaxies and active
galactic nuclei. She values the power of the
scientific method, the history of science and
the necessity of skeptical inquiry. As a self-professed
space cadet, Summer grew up dragging friends
and family out at all hours of the day or
night to look up at the sky. In her previous
life she was a rocket scientist, but now
enjoys getting paid to spread her love of
space with anyone who will listen. She
attempts to blog at Newtonianism
for the Ladies, tweets as @Summer_Ash,
and is the in-house Astrophysicist for The
Rachel Maddow Show.
The views expressed are those of the
author and are not necessarily those of
Scientific American.
© 2011 Scientific American,
a Division of Nature America, Inc