Note: Descriptions are shown in the official language in which they were submitted.
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Case 2918
DESCRIPTION
FREEZE-DRIED COFFEE WITH A ROAST AND
GROUND_APPEARAN~E AND A METHOD THEREFOR
05 TECHNICAL FIELD
The present invention relates to a method of
producing a freeze-dried coffee having the appearance
of roast and ground coffee. Specifically, this
invention involves a process of instantly freezing a
portion of substantially frozen coffee e~tract by
spraying a cryogenic fluid thereon. The aqueous
coffee extract frozen in this manner is ground and
freeze-dried according to a method well known in the
art.
BACKGROUND ART
Methods of producing the desired color freeze-
dried coffee, either light or dark-colored, are
known in the art. It is recognized that rapid
freezing of a water-bearing substance promotes the
distribution of a great number of small ice crystals
and slow freezing produces a lesser number of larger
ice crystals. With respect to freeze-dried coffee,
it is estab'ished that a rapidly frozen coffee
extract containing smaller ice crystals yields a
light-colored soluble coffee whereas a slowly frozen
extract containing larger ice crystals provides a
darker coffee.
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A dark-colored freeze dried coffee has generally
been preferred and much effort has been directed
towards producing such a coffee, usually by controlling
the manner of freezing the coffee extract. For
05 example, U.S. Patent No. 3,253,420 to ~eGeorge
discloses a method of freezing coffee extract on a
chilled metal belt over an approximately 15 minute
period. A method of freezing whereby coffee extract
is agitated while being chilled from its ice point
to a temperature below its eutectic point over a
period of between 15 minutes and 30 minutes is
disclosed in U.S. Patent No. 3,399,061 to Lutz.
More rapid methods of freezing coffee extracts which
also darken product color are known, such as the
disclosure of U.S. Patent No. 3,443,963 to Simon et
al. wherein coffee extract is first chilled to about
minus 5C and held at that temperature for nearly 20
minutes prior to rapid freez'ing. Another disclosure,
U.S. Patent No. 3,966,g79 to Katz et al., describes
a layered freezing process wherein the upper portion
of a fast frozen extract layer is melted by having a
layer of warm coffee extract placed on top and both
layers are then frozen prior to the addition of the
next layer.
Although the dark-colored freeze-dried coffee
is generally considered as more nearly resembling
the appearance of roast and ground coffee in comparison
to a light-colored freeze-dried coffee, inspection
of roast and ground coffee reveals that it is actually
composed of particles of many different shades,
ranging from light to dark coffee color. A freeze-
dried coffee of only one color, even though it is
dark, cannot resemble the appearance of roast and
ground coffee as nearly as a freeze-dried coffee
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comprised of light- and dark-colored freeze-dried
coffee particles.
It is an object of the present invention to
provide a method of producing a freeze-dried coffee
05 having the appearance of roast and ground coffee
which freeze-dried coffee is comprised of light- and
dark-colored freeze-dried coffee particles.
DISCLOSURE OF THE INVENTION
A method of producing a freeze-dried coffee
having the appearance of roast and ground coffee has
now been discovered. The method involves instantly
freezing a portion of substantially frozen coffee
extract by spraying a cryogenic fluid thereon. The
coffee extract so frozen is ground and subse~uently
freeze-dried.
The initial step in the method of the present
invention is freezing a portion of an aqueous coffee
extract layer while leaving the remaining portion
substantially but not completely frozen solid. The
term "substantially frozen" is intended to mean that
state of the coffee extract wherein there is virtually
no free water present but said extract is not yet
frozen solid to the point of being brittle. Said
freezing may conveniently be carried out by placing
the coffee extract layer in a pan and chilling the
underside of the pan. In this way, the lower portion
of the extract layer is frozen solid before the
upper portion of the extract layer is completely
frozen solid. Most preferably, the freezing is
carried out on a continuous, moving metal belt as
described in U.S. Patent No. 3,253,~20 to De&eorge.
The continuous metal belt is chilled underneath by a
sexies of brine pans maintained at progressively
lower temperatures along the length of said belt.
Here again, the lower portion of the coffee extract
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layer may be frozen while the upper portion of the
layer is substantially but not completely :Erozen
solid. The cryogenic fluid is conveniently sprayed
or poured on the surface of the coffee extract at
05 that point along the length of the belt where the
preferred extent of freezing is attained.
What is meant by "cryogenic fluid" is a fluid
which results from the condensation of the typically
inert gases, which gases liquify at extremely low
temperatures. For instance, liquid nitrogen which
condenses at minus 196C, is particularly well
suited for use in the present invention. Cryogenic
fluids are useful because of the extremely low
temperature at which they evaporate, which in effect
instantly freezes the subs-tantially frozen coffee
extract when sprayed thereon. Said fluids rapidly
evaporate from the surface of the instantly frozen
coffee extract, leaving no residual trace in either
the frozen or finished coffee product. Even if
residual traces of the cryogenic fluid were to
remain in the frozen coffee extract (though, as
noted, no such traces do in fact remain), the
preferred use of liquified inert gases prevents any
possible contamination of the freeze-dried coffee
product.
The cryogenic fluid is applied to the sub-
stantially frozen portion of the coffee extract
surface in the form of a spray. Such a spray is
effective in instantly freezing only the upper
portion of the extract layer, which upper portion is
substantially yet not completely frozen solid prior
to application of the fluid. The net effect of
spraying the cryogenic fluid on the surface is to
create a light-colored instantly frozen coffee
extract layer on top of the darker colored conventionally
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frozen coffee extract layer. A spray of cryogenic
fluid is convenient for controlling the ~uantity of
said fluid applied, as well as providing for the
even distribution of the fluid to the surface of the
05 coffee extract layer. Proper control of the amount
of cryogenic fluid applied is important in conserving
the valuable cryogenic fluid.
After the cryogenic fluid has been applied to
the coffee extract, the completely frozen coffee
extract layers are removed or discharged from the
apparatus-in which it is frozen and subse~uently
ground. The purpose of grinding the frozen extract
is to both facilitate the freeze drying operation
and provide a homogenous mixture of instantly frozen
and more slowly frozen coffee extract particles. An
ob~ect of the invention is to provide a method of
producing a freeze-dried coffee comprised of light
and dark-colored freeze-dried coffee pa:rticles.
Grinding of the frozen extract provides for the
random disperson of the light-colored and dark-colored
particles by the mixing action that takes place
during the size reduction of said frozen coffee
extract. The actual method of grinding is not
particularly important; a hammer mill such as is
known in the art is particularly convenient for
grinding the frozen extract.
The ground, frozen coffee extract is then
freeze-dried according to methods well-known in the
art. Freeze drying is basically the removal of
water from a frozen article by subliming the water
directly from the frozen into the vapor state. Such
drying is typically carried out in a vessel maintained
at a sufficien-tly low pressure as to permit sublimation.
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The method is disclosed, for example, in U.S. Patent
No. 3,365,806 to Pfluger et al. After drying, the
product is removed from the freeze drying vessel and
the freeze-dried coffee having the appearance of
05 roast and ground coffee is obtained.
As an alternative, the frozen coffee extract
layer may be freeze-dried in whole form and sub-
sequently dried. Such an embodiment is not preferred
because of the relative inefficiency of freeze
drying a whole frozen slab. The grinding operation
is not particularly efficient after freeze drying,
with the resulting generation of a considerable
amount of coffee fines. It is, however, possible to
operate the process according to this embodiment if
sufficient control of the coffee fines is provided.
Freeze-dried coffee particles of at least three
different colorations are seen to result from the
method of the present invent;on. As hereinabove
described, the frozen coffee extract is comprised of
two layers, a light and a dark-colored layer, after
the application of the cryogenic fluid. So, on
grinding, particles are formed at least frcm the
dark-colored layer and the light-colored layer,
giving two distinct particle colorations. A third
coloration is provided from that portion of the
frozen extract comprising the boundary of the light
and dark colored layers. Particles produced therefrom
will be dark-colored on certain faces and light-colored
on others. The particles of three colorations are
mixed homogeneously during grinding so that upon
drying, a freeze-dried coffee having the appearance
roast and ground coffee is produced.
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BEST MODE FOR CARRYING OUT THE INVENTION
, . _ . .... . _ . .
The following example is meant to demonstrate
certain aspects of the present invention. The
exarnple is not intended to limit this invention5 beyond what is claimed below.
EXAMPLE
1. A l9mm deep layer of aqueous coffee extract
(25% by weight soluble solids) was placed in a
stainless steel tray maintained at minus 30C. The
extract was maintained at minus 30C until the
bottom of-the layer was frozen solid but the upper
portion was still tacky.
2. Liquified nitrogen was poured on top of
the extract layer so as to cover the whole surface
of said layer, instantly freezing the tacky upper
portion. The liquified nitrogen was subsequently
allowed to evaporate.
3. The frozen coffee extract was reduced in
size by forcing the slab through an 8 mesh (U.S.
Standard Sieve Screen). The frozen particles were
shaken so as to distribute the different colored
particles uniformly throughout.
4. The frozen coffee particles were then
freeze-dried in a laboratory freeze dryer maintained
at a pressure of about 250 microns and a platen
temperature of 42C for a period of 16 hours.
The resulting freeze-dried coffee had different
colored particles and was characterized as having
the appearance of roast and ground coffee.
