Note: Descriptions are shown in the official language in which they were submitted.
194~
DESCRIPTION
PROCESS FOR PREPARING MICROPOROUS
DRY SOLUBI.,E COFFEE PRODUCT
Technical Field
05 The present invention relates to soluble coffee.
More particularly~ it relates to a process for
preparing a dry soluble coffee product in the form
of particles or granules which have a unique micro-
porosity capable of sorbing and retaining volatile
aromatic compounds and releasing these volatile
aromatic compounds in a controlled manner.
Back~round Art
Many commercial soluble coffee products are
enhanced wi~h volatile aromatic compounds by combining
the soluble coffee product with pure coffee oil or
aroma-enriched coffee oil so as to provide the
soluble coffee product with an aromatic quality more
like that of roasted and ground coffee. However,
aromatizing a soluble coffee product with coffee oil
presents plant processing problems in recovery of
--2--
the oil from the roasted coffee beans in handling
the resulting presscake, and in storage of the oil.
Generally, headspace aromatization of soluble
coffee products without the use of coffee oil as an
05 aroma source or aroma carrier has not met with
marked commercial success. It is known that con-
ventionally produced soluble coffee solids lack the
capacity or property of sorbing, retaining and
releasing volatile aromatic compounds such as are
contained in, or added to, coffee oil.
The prior art also discloses porous soluble
coffee particles having the capacity to sorb large
quantities of volatile aromatics, to retain the
aromatics for extended periods o~ time, and subse-
quently, to release the aromatics under repeatedin-use conditions such as may be encountered in
opening and closing a container in which the particles
are packaged are described and claimed. The aromatized
soluble coffee particles may be added in small
amounts and uniformly admixed with unaromatized
soluble coffee solids to provide a soluble coffee
product with a desirable coffee aroma such as the
aroma of freshly roasted and ground coffee.
The porous soluble coffee particles are charac-
terized by having an average diameter of less than200 microns and a microporous structure wherein the
most probable radius of the pores is 150 A or less
and the pore volume per gram of dry soluble coffee
solids is from 3 to 30 microliters per gram. These
microporous structured soluble coffee particles are
prepared by instantaneously freezing an aqueous
extract or solution of coffee solids as by spraying
--3--
the extract solution into a cryogenic fluid and
subsequently freeze-drying the frozen particles,
spheres or granules.
While ~he methods described and claimed in the
05 hereinbefore mentioned patent applications are
capable of producing microporous structured soluble
coffee, there would be advantages to a method or
process whereby microporosity, pore volume and
surface area might be increased.
Disclosure of the Invention
It has now been discovered that a microporous
dry soluble coffee product may be obtained by -
(a) spraying an aqueous extract or solution of
autoclave coffee solids into an anhydrous
organic solvent so as to dehydrate the
extract and form microporous particles or
granules of soluble coffee solids;
(b) recovering the dehydrated extract in the
form of microporous particles from the
solvent; and
(c) removing residual solvent, under vacuum,
from microporous particles.
The resulting dry soluble coffee particles are
found to have a microporous structure which makes
them suitable for sorbing, retaining and releasing
aromatic volatile compounds.
Soluble coffee particles prepared by the process
are found to possess a micropore volume (radii of
~150 A) of from about 5 to 560 microliters per gram
and a surface area of from about 7 to 210 m2/g.
--4--
The invention offers an improved me~hod for the
preparation of discrete microporous structured particles
in that expensive and costly freeze-drying equipment is
not required.
05 By spraying an extract or solution of autoclave
coffee solids into an anhydrous organic solvent 9 a
specific microporous structure of extremely high
surface area may be formed which structure may also
be further controlled by modifications of spraying
pressures, extract makeup, extract concentration,
solvent type and solvent temperature and the like.
The resulting microporous dry product exhibits
the ability to "fix" various aromas.
Best Mode for Carrying Out the Invention
The starting extract may be a water solution of
autoclave cofee solids at lO to 60% soluble solids,`
formed by any one or a combination of various tech-
niques including percolation/extraction of roasted
and ground coffees, followed by autoclave steaming
of the columns, usually at 180C, dissolving previously
dried soluble autoclave coffee solids in water, and
the like. Evaporation may be used to achieve desired
concentration with any of the foregoing. Generally,
the extract temperature is maintained between about
32 to 30C.
Any anhydrous organic solvent such as ethanol,
methanol, isopropyl alcohol acetone and the like may
be employed provided it serves as a dehydrating
medium and it is a solvent in which coffee is
relatively insoluble. Preferably, ethanol is employed.
Aqueous solutions of soluble autoclave coffee
solids (25 to 35%) are sprayed into a vessel con-
taining pure alcohol (ethanol or methanol) preferably
using high pressure nozzles (600 to llO0 psig). The
.1 ~t.J~9
--5--
alcohol is maintained at ambient temperature but
preferably it is cooled with addition of li~uid
nitrogen to drop its temperature down to about
-100C. The ratio of aqueous extract to alcohol is
05 kept around or below 1:20 to obtain a fairly dry
solid. At the end of the spraying period, usually a
few minutes, the alcoholic suspension is allowed to
settle for about one hour (and to bring the temperature
to above 0C if it was lowered before spraying).
This is followed by a quick filtering of the de-
hydrated solid and finally an overnight vacuum
solvent drying in a vacuum oven. The temperature of
the oven is kept between ambient temperature and
90C .
The microporosity of the soluble coffee product
is characterized by determining the nitrogen ad-
sorption isotherm at liquid nitrogen temperature.
From the isotherm the following parameters are
calculated:
i) Surface area (m2/g);
ii) pore volume (~l/g);
iii) pore volume distribution (aV/ar, in ~l/A);
and
iv) pore surface area distribu~ions (m2/g for
a given pore-range).
All the above parameters are printed out by a
Micromeritic 2500 Digisorb*, available from Micromeritics
Instrument Corporation. However, the pore volume
distribution may be recalculated to be aV/ar rather
than av as given by the Digisorb.
Details of the pore size analysis are given in
applicant's Canadian Application S.~. 339,558,filed
Nov . 9/79 . The pore surface area distribution (~Sp)
is related to pore volume distribution ~Vp of that
* Trade Mark
--6--
particular group of pores) by the following equation
QSp = ~
rc
where rc is the average pore radius of that group of
05 pores.
Upon analysis the microporous structured products
are found to have pore volumes of from about 5 to
560 microliters pèr gram and micropores whose radius
is S150 A and surface areas of from about 7 to
0 210 m2/g.
The volatile aromatic compounds associated with
coffee, whether natural or synthetic, to be sorbed
on the microporous structured product may be derived
from many sources well-known to those skilled in the
art. Depending on the method of contact to be
employed, the compounds may be present as a component
of a gas, a liquid condensate or a condensed frost.
The method of contacting the microporous particles
with the volatile aromatic compounds for the purpose
of sorbing aroma within the particles can also be
many and varied. The use of high pressure and/or
low particle temperatures may be employed in order
to maximize the quantity of aroma sorbed or to
shorten the period of time required to achieve a
desired level of aromatization.
The microporous structured soluble coffee
product prepared by the process of the invention has
the capability of sorbing as much as 2% by weight of
volatile aromatic compounds. This is, in general,
in excess of that which is required and, depending
on how the aromatized soluble coffee solids are
utilized, the aromatized particles will contain
volatile aromatic compounds at a level of from 0.05
to 20 milligrams per gram of solids, 0.2 to 0.5% by
weight.
-7-
Example 1
One hundred milliliters of a coffee extract
containing 33% by weight soluble autoclave coffee
solids is sprayed by means of a glass chromatographic
05 nozzle into a large vessel containing 3.8 liters of
pure ethanol. The ethanol was at room temperature
and was stirred during the spraying operation.
Thereafter particles of soluble coffee were filtered
from the ethanol and these particles were put in a
vacuum oven (25 inches Hg. vacuum and about 90C)
overnight to remove residual ethanol. The resulting
particles were found to have a microporous structure,
a pore volume of 66.2 microliters per gram (rS150 A) and
a surface area of 42.2 m2/g. The particles were kept
lS out of contact with moisture and contacted with
grinder gas frost at a level by weight of 2 parts
frost to 1 part of particles in a Parr bomb heated
to about 20C. The resulting aromatized particles
were combined and packaged with unplated and un-
aromatized spray dried coffee agglomerate at a level
of about 0.5% by weight. The jar aroma possessed by
this sample after one week storage at room temperature
was found to be comparable to week-old, grinder
gas-enriched, oil-plated agglomerate.
Example 2
In this Example only high purity autoclave
coffee solids are used. This material is practically
insoluble in pure ethanol. The process is thus
essentially a dehydration process with no or very
little etching (since caffeine and chlorogenic acid
are relatively soluble in ethanol).
Using a high pressure (600 to 1100 psig) a 33%
coffee autoclave solids solution is sprayed into
ethanol at ambient temperature. Microporous particles
having a surface area of 40 m2/g are produced.
~1C~9~1
Significantly higher surface areas (over 200 m~/g)
are obtained by spraying these autoclave coffee
solids into cold ethanol (about -80C).
The dry particles were found to have a microporous
05 structure pore volume ranging from 5 to 560 micro-
liters per ~ram (rS150 A) and a surface area ranging
from 7 to 210 m2/g.
The solvent-free dry particles were subsequently
chilled in dry ice under a dry atmosphere and mixed
with coffee grinder gas frost. The chilled particles,
were then pac~aged in glass jars with unplated~
agglomerated spray-dried coffee solids at the level
of 0.75% by weight of spray-dried solids. Upon
storage initial opening and during a standard seven-day,
in-use cycle, a pleasing headspace aroma was noted.
Industrial Applicability
The microporous structured soluble coffee
product prepared by the process of this invention is
utilized as a sorbent for volatile aromatic compounds.
The process offers an improved method for the
preparation of discrete particles of the microporous
structured soluble coffee product.
