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Coffee: To Freeze or Not to Freeze
Does freezing preserve coffee used for espresso?
By Ken Fox
Ken Fox and Jim Schulman repeated the experiment described in this article in March of 2009,
with some modifications that extend the usefulness of the results to include lower dosing,
a longer interval of freezing, and the use of higher end grinders. They published their results in the forums under the title of
Freezing Espresso Coffee, Part Two.
Jim elaborated on how to correctly interpret the results of such
experiments in A note on comparison tests. —HB
Coffees stocked on grocery store shelves are frequently labeled with
"Best By" freshness dates that represent anything from days to months
after actual roasting. The coffees sold from open bins may turn over
quickly, but frequently are not fresh when stocked and regardless will
suffer from light exposure and oxidation. There are few choices for
coffee aficionados who prize freshness.
When coffee aficionados talk about freshness, what do they mean? What
are they looking for? It goes without saying that espresso made from
fresh coffee has more flavor, aromas, sweetness, and produces richer and
more voluminous crema. What's not obvious to all espresso lovers is the
fact that fresh coffee is easier to extract correctly. Telltale signs of
stale coffee are flat, monotonic flavors, bitterness, woody / cardboard
tastes, and little or no crema. Any experienced home espresso enthusiast
has experienced these things first hand— bleech! If you're serious
about exceptional espresso, it starts with exceptionally fresh coffee!
Stored at -20°F
Sourcing truly fresh coffee can be difficult. The options include:
Buy locally - if you are fortunate enough to have a good
local roaster who values freshness.
Order online - many roasters have enthusiastically embraced
the online espresso community. Their coffees are roast dated and there
are many choices. The drawbacks include the shipping cost and matching
your consumption patterns with roasting and delivery schedules.
Homeroasting - in an effort to have even fresher coffee, many
home consumers roast their own coffee from green beans, a practice that
went out of fashion around a century ago. Green coffees are also widely
available online. Many espresso enthusiasts embrace homeroasting as the
best solution to the problems of cost, variety, and most importantly,
Whether you roast coffee at home, purchase it locally, or buy it
online, proper storage is important. Storage for a few days is
straightforward for small quantities of coffee, but what about longer
term storage of larger quantities? Freezing slows the relentless
degradation of many perishable foods. This article attacks the question, "How well does it preserve the
precious characteristics of fresh coffee that espresso lovers adore?"
The freezing debate
Few topics in coffee have been debated as much as freezing. Coffee
has a limited shelf life, even shorter when it is used to make espresso.
Most serious enthusiasts feel that this shelf life is considerably less
than a month, and many agree the shelf life at room temperature is
limited to as little as 10 days after roasting. There is no evidence
that simple valve bag packaging at room temperature significantly
extends storage life for consumers who care about coffee freshness.
Given its perishable nature and the fact that many consumers have
limited access to good fresh coffee, it is only natural to want to
extend the shelf life long enough that a given batch can be considered
usable, near its peak of freshness.
Freezing and refrigeration of roasted coffee are hotly debated based
on anecdotal experience. Some academic research has been published, most notably by Sivetz,
however his methods, including the use of a vacuum and extreme cold
(~-40°F or C) are not available to most individuals, especially in
I prefer to make several batches in succession with my 500 gram
sample roaster because of the required heating and cooling time, which
makes small volume roasting impractical. As a result, I've adopted freezing
as a storage technique, and am constantly switching back and forth
between previously frozen and never frozen coffee. I have not noted an
obvious difference between these coffees prepared as espresso, however I
wanted to formally test my observations. This article presents the
structure and results of an experiment to demonstrate the effectiveness
(or lack thereof) of freezing very fresh coffee in a home environment to
extend the shelf life of this perishable product.
Key elements of a meaningful test
An ideal way to compare two different consumable items is to be
presented with both of them simultaneously. This is the very nature of
blind tasting experimentation. Fortunately I have two similar espresso
machines that can be adjusted to produce nearly identical espresso
extraction parameters. Since I have the good fortune to own this
equipment and the desire to get to the bottom of this freezing issue, I
decided it was high time to explore this subject in a more scientific
manner. Out of this curiosity was born this experiment, a definitive
blind tasting trial comparing espressos prepared from coffee that was
previously frozen for periods of four or eight weeks, to freshly roasted
coffee during its normal shelf life, in this case between 4 and 8 days
As in any study using the scientific method, one has various factors
that may confuse or confound the results. Failure to account for the
variables may result in false impressions of real differences when in
fact none exist, or may mask real differences. It is therefore important
to consider these variables in the design of the experiment from its
very conception. By doing so, one acknowledges their presence and sets
up the experiment in a way that these variables cancel themselves out.
Tasting station with
Consistency - espresso making by its nature has some
variance. Since it is difficult if not impossible to hold all factors
equal and hence to get identical shots each time, one has to consider
this normal variation. Important factors to
manage include the brew temperature, coffee dosage, extraction time,
and the shot volume produced. Becoming proficient in making espresso
can require years of practice.
Blind tasting - knowledge of differences in preparation
will subtly influence taste reports. If you've ever attended a coffee
cupping, you may have noticed how one word from a participant can
influence the comments of all present ("Nice chocolates!" followed by a
chorus of "cocoa", "Hersey's Kiss" etc.) Withholding knowledge of the
difference between samples from the taster reduces the possibility of
their observations being influenced by preconceived notions.
Experimental design and data analysis - constructing the
test such that the observations, when analyzed, can yield results that
prove to be genuine and unlikely the result of chance alone. This
requires specialized skills, most notably an understanding and facility
with the use of statistics.
Last but not least, the experiment itself must be designed in a way
to test the manipulated variable, to balance those factors that might
confuse the results, and to be practical.
We held four tasting sessions, each lasting approximately three
hours. They were composed of 16 paired double shots prepared
consistently and simultaneously on the two espresso machines and
presented to the taster in a blind fashion. The taster did not know
which coffees he was tasting or which pieces of equipment were used,
just that one espresso was made from previously frozen coffee and the
other was not. Each taster would have 8 paired shots to taste in a day's
session; 4 pairs of shots compared coffee previously frozen for 4-weeks
to never frozen, and the other 4 pairs of shots compared coffee
previously frozen for 8-weeks to never frozen. Grinder changes were
minimized as much as possible in the design to both avoid wasting coffee
and the need to constantly clean grinders. The shots were alternated to
the tasters so that the tasters did not have undue fatigue of their
ability to appreciate differences in espresso. This was important
because espresso is a very intense beverage, and too
many comparisons within a very short time can diminish the ability to
appreciate differences. A total of 64 paired shots of frozen versus
never frozen coffee were tasted and compared over the four day course of
When presented with the two espressos, the taster was required to
compare them according to three factors: the crema, the intensity of the
aroma and taste, and the overall preference. These tasters were
instructed to make these comparisons quickly but carefully, in keeping
with the way that such comparison taste studies are done in industry
where this method is very well established.
A few additional words about the shot preparation and the freezing
are warranted. Double espressos were prepared with approximately 18
grams of coffee lightly tamped and ground in a way to produce 1.25 to
1.50 ounce shots within a period of 20 to 30 seconds, occasionally as
long as 35 seconds, with very few shots at the shorter end of this
spectrum. The previously frozen coffee was frozen immediately after
roasting in a very cold chest freezer, at a temperature of around
-15°F (-26°C). Frozen coffee remained in the freezer for periods
of either four or eight weeks.