HOW TO BE
COOL
Cooling Methods and Their
Impact From Roast to Cup
by Christopher Schooley
photos by Nolan Dutton of Ozo Coffee
T
he roasting process has many stages:
drying, browning reactions, caramelization,
first crack and cell expansion, to name
a few. Each stage plays an important part in the
development of the flavor profile of the coffee—the
whole roasting process is development. The stage
that begins with the first crack and includes the
beginning of caramelization is referred to as the
“development stage” by some roasters, but this can be
misleading as it diminishes the importance and the
impact of the other stages during roasting.
continued on page 40
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roast
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HOW TO BE COOL | Cooling Methods and Their Impact From Roast to Cup
(continued)
With that thought in mind, at the end of
food item continues to cook and adds
issue. If you cool it too slowly, the long
overlooked is the cooling stage. While it
the roast, the coffee has quite a bit of energy
as much as 10 to 15 degrees of internal
series chain polymers, sugars, fructose
doesn’t happen in the roaster itself, properly
and momentum itself, so much so that even
temperature after being removed
and glucose will find other constituents
cooling the roast has a dramatic impact on
when removed from the roasting chamber
from the heat. This may change the
to link up with in the coffee, and they
the cup.
it’s still changing, only now it’s doing that
development and degree of doneness
are not as soluble.”
in an uncontrolled environment—that is,
past the point desired.
One such stage that can be easily
The roasting process is an exchange
of momentum. Energy is built inside the
if the core temperature of the beans is not
roasting chamber and then transferred to
actively being brought down.
the coffee as it progresses through the roast.
In cooking, this is called carry-over. The
Without continuing to add energy
Staub is saying that if a coffee takes
Cooling
with Air
The most common cooling method used by
too long to cool, there’s not as much
small-craft coffee roasters is cooling with
soluble sweetness to draw from when
air. Although some fluid-bed roasters do
however, the longer it takes to cool to
brewed. Through extensive testing done
include a water quench as well as a cooling
room temperature, the more the coffee
by Staub, as documented in the lecture
will continue to change from when the
above, by me and by a number of other
roast was initially stopped. Delayed
roasters and roaster manufacturers
cooling may result in an undesirable
that I spoke with for this article, it has
baked or dried-out character, but
been duly noted that getting post-roast
generally, sweetness is the most
cooling times down to 4 minutes or less
notable difference. This is a common
provides a noticeable difference in the
roasting anecdote, but one that has
sweetness of the cup.
The difference in cooling from
through various trials conducted by
between 5 minutes and 4 minutes is so
roasters and roaster manufacturers.
dramatic that the panel that tasted the
cooling tray with a perforated bottom. This
is connected to a blower that pulls air from
the room through the just-roasted coffee as
a pivot arm stirs the coffee to create a more
to the coffee, it will eventually cool;
been demonstrated time and again
tray, most drum roasters purely use a
even cooling for the whole charge.
Most roasters view the blower (motordriven impeller to suck or blow large
continued on page 42
coffees in the experiments Staub created
The most common
cooling method
used by small-craft
coffee roasters is
cooling with air.
felt the sweetness had increased by at
least double by shortening the cooling to
less than 4 minutes.
Joseph A. Rivera, founder of
the online coffee science resource
coffeechemistry.com, says that because
the soluble/insoluble chemistry
described above happened during
roasting at temperatures greater than
400 degrees F, and not during cooling,
cooling itself might not be the cause of
this greater perception of sweetness.
He adds that if rapidly cooled
coffees do possess more sweetness, it
is more likely due to certain aromatics
being preserved by the quicker cooling
process. “Aromatics are temperature
In a lecture on cooling at the SCAA
are exposed to higher temperatures they
Carl Staub spoke about the impact of
will also release more aromatics, some
proper cooling on sugar development
of which may be sweet in character and
during the roasting and cooling
ultimately lost in the cup,” Rivera says.
process:
“The primary sugar in coffee is
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roast
dependent, meaning that when beans
Expo in 2002, Agtron managing partner
One concern about cooling
is fracturing the cells. According
sucrose. During the roasting process
to Stephan Diedrich of Diedrich
you fracture the sucrose, and you want
Manufacturing, in order to fracture
to caramelize it or polymerize it in the
the cells the coffee would have to be
scientific term. But, you also have to
cooled almost instantly, which would
maintain solubility. If it doesn’t come
take a great deal of resources to remove
out when you put water into it, it is
the energy in the beans and bring the
not going to be a sweet cup. Having the
temperature down at that required
sugar there is one issue, and being able
speed. So, the bigger issue is still cooling
to get it out with hot water is another
in time.
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HOW TO BE COOL | Cooling Methods and Their Impact From Roast to Cup
(continued)
volumes of air) as the key component in this cooling setup, and in
Many of these roaster models are capable of cooling the coffee
amounts of coffee in certain areas while
many ways, it is. As much air as possible has to be moved through a
to room temperature in less than 4 minutes, but one of the
also creating areas where the bed is much
cooling tray full of coffee freshly released from the roasting drum at
most commonly cited issues, if cooling times are not below the
shallower—where more air will move
more than 400 degrees F. There are a number of roaster models which
4-minute mark, is whether or not the roaster has a cooling-
through faster. Air always wants to take
use a single blower for both the roasting drum and the cooling tray,
specific blower.
the path of least resistance.
and include a damper for switching the function between the two.
Truly the biggest impact
on cooling performance is
maintenance, and the health and
condition of the airflow systems.
Beyond the blower, though, there could be a number
Roast says his company designs its
temperature. The ambient temperature in a non-climate-
cooling trays to cool coffee faster by using
controlled warehouse may vary by as much as 30 degrees
a relatively smaller-diameter cooling
between summer and winter. The pivot arm stirring the roasted
tray with a strong blower. He says, “In
coffee in the cooling bin can also be considered. If this arm is
the smaller tray the air velocity is much
spinning too fast, it could actually slow down cooling times.
higher for better wind chill factor. It
Diedrich sometimes recommends stopping the stirring arms
travels through a deeper bed of beans, so
after the coffee has been evenly distributed, about a minute, in
there’s more exposure, and there are no
order to pull more air more quickly through more coffee.
open screen areas behind the sweeps on
In Staub’s 2002 SCAA lecture, he talks about using a
the stirring arms where the air can take a
frequency drive on the stirring arm and adjusting the speed
shortcut. It works very well; cooling times
of the armature throughout the cooling process for optimal
can actually be under 3 minutes.” (He cites
results, starting faster and slowing down as the coffee cools.
a 450-degree-F start point on a 65-degree-F
The most important consideration in this regard is the even
day in low humidity.)
distribution of the batch. This is one of the reasons a more
rapidly spinning arm slows down cooling; it collects greater
42
roast
Mark Loring Ludwig of Loring Smart
of other impacts on cooling times, such as ambient air
continued on page 44
Blower unit for a Diedrich IR12 after regular cleaning and maintenance.
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HOW TO BE COOL | Cooling Methods and Their Impact From Roast to Cup
Truly the biggest impact on cooling performance is maintenance,
and the health and condition of the airflow systems. Diedrich stresses
the idea that the entirety of the roaster is all one system, and regular
maintenance throughout that system is the key to proper cooling
times. At each step of the cooling process there is the opportunity for
particulate buildup from the smoke, steam and broken bits of coffee.
Loring mentions that his cooling tray design also played into
(continued)
exhaust cap isn’t too restrictive, which could lead to greater
buildup.
cycle in a cooling tray. The purpose of the quench, usually in the
Water Quenching
his desire for ease of maintenance. The smaller diameter and design
adjustments to the paddle assembly allow the screen of the cooling
tray to be easily lifted out for direct access and quick cleaning.
Daily, weekly and monthly maintenance on a cooling system is
vital for performance. The perforated bottom of the tray can easily
become blocked as those perforations fill with bits of coffee or oil.
Scrubbing and wiping down the tray regularly will go a long way to
maintaining cooling performance, and cleaning under the tray each
time it’s brushed, scrubbed or wiped down is important to make sure
any particulate freed during the process doesn’t travel further down
along the system.
Removing any residual oil should be part of safety procedures,
as well as quality control to prevent oil from turning rancid and
contaminating other batches. Cleaning the impeller on the blower
and every point in the exhaust is key. Diedrich says it’s important
to clean the exhaust up to the roof regularly and to check that the
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roast
To clarify, water quenching is really just a step in the cooling
process, and a water-quenched coffee generally finishes its cooling
In many specialty roasting circles, water quenching, the other
common cooling method, is looked down upon and generally
completely disregarded. Its dismissal has become one of those
specialty coffee tales that gets passed on from roaster to roaster
without any exposure to, or understanding of, the actual practice.
One of the reasons for this dismissal of water quenching is the
misconception that it adds moisture back into the coffee. While
some roasters may have, or currently do, use quenching to add
weight back to the roasted coffee, properly water quenching coffee
for cooling purposes may not involve any absorption. One roaster
who uses water quenching in cooling (and who chooses to remain
anonymous for proprietary reasons) says he noticed when using
a quench with darker roasts where the coffee did absorb some
measurable moisture, the harsher flavors of the darker roast were
reduced while the sweetness was more pronounced.
roasting chamber or just at the door at the drop, is simply to halt the
increase in internal temperature. It takes further cooling with air to
actually bring coffee down to the prescribed (room) temperature.
In water quenching, the coffee is not soaking to bring the
temperature down. Most commonly, the water is sprayed toward
the charge as a mist for 30 to 90 seconds. This generally evaporates
immediately, given the high temperature of the beans and the
environment.
Water quenching is much more of an issue with larger roasters
and darker roasts, yet Diedrich recommends it in any machine with
more than a 25-kilo capacity.
Water quenching is really just
a step in the cooling process, and a
water-quenched coffee generally
finishes its cooling cycle
in a cooling tray.
Another roaster I spoke to who declined to give his name for
proprietary reasons says he began experimenting with water
quenching in order to control his darker roasts at the final stage.
Following success with the darker roasts, he started looking at his
others and was impressed with the cup results at all roast levels after
using water quenching to lower cooling times across the board.
Quenching is carefully monitored and compared to nonquenched batches to ensure there is no moisture being absorbed in
the process. This roaster found all of his roasts sweeter while water
quenching helped to shorten cooling times. He also noted there was
no noticeable impact on the shelf life of the coffee—another of the oftcited concerns with quenching.
Another question that has come up in trials and in a 2007 study
by the Institute of Food Science and Nutrition at the Swiss Federal
Institute of Technology (ETH) in Zurich, Switzerland (titled, Influence
continued on page 46
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HOW TO BE COOL | Cooling Methods and Their Impact From Roast to Cup
(continued)
of Water Quench Cooling on Degassing and Aroma Stability of Roasted Coffee), is the impact of water
quenching on degassing and shelf life. While quenching seems to perhaps lead to quicker
degassing, it may not be directly linked to shelf life of roasted beans. Even so, the roaster
who spoke to me about water quenching lessening the harshness of darker-roasted coffee
said his research had shown that degassing was longer with water-quenched coffees.
He says, “Higher moisture slows degassing times as water inhibits the flow gasses
in coffee beans. If quenching results in higher moisture in coffee, then it does indeed
shorten shelf life. Water is a medium for reactions, and if there is more water in coffee
then it will encourage those reactions.”
That said, proper and timely cooling does have a noticeable impact on shelf life,
as longer cooling times lead to more rapid oil expression, which then leads to quicker
Cool Out
Like almost everything in coffee roasting, the true quality impact of cooling is ripe for
further research. Though the 4-minute magic number seems to be consistent with all of
the roasters I spoke with for this article, there are other matters to regard. Everything
from the age and density of the green coffee to differences in roast profiles could have a
dramatic impact on whether or not that cooling time is truly ideal.
That said, experientially, a quicker cooling time results in a sweeter cup. We’ve been
unfairly dismissive of water quenching, and it warrants further consideration. It could
be cooler than we thought.
degradation. There are a number of other factors at play here, including the moisture
content of the green coffee to begin with, as well as the actual roast profile.
Diedrich says another positive impact of water quenching is that air-quality
developing resources and online content and offers roaster support. He also works for the SCAA as the coffee
thermal oxidizer (afterburner), along with gas consumption. Remembering that the air
design and experience coordinator, and is working to open Troubadour Malting and Malt Roasting in Fort
and any smoke from the cooling tray also has to go through the exhaust and afterburner,
Collins, Colorado. He can be reached at [email protected].
in some cases, a water quench system can help reduce smoke present in the cooling tray.
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roast
CHRISTOPHER SCHOOLEY thinks he is a cool dude. He works for Coffee Shrub/Sweet Maria’s
restrictions become more stringent. Water quenching can help reduce the workload of the
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