Extraction method

A process for extraction of a soluble component from a dried food material, which process includes: PA1 providing: PA2 a dried food material to be extracted, PA2 an extracting liquid, and PA2 an enriching liquid consisting essentially of a solution of the soluble component to be extracted; PA1 forming a pool of the enriching liquid at a lower end of a counter current extractor including a rotary screw conveyor mounted within an inclined or vertical housing; PA1 feeding the dried food material into the lower end of the counter current extractor to contact the pool of enriching liquid wherein enriching liquid is absorbed by the dried food material to form a hydrated, enriched food material; PA1 conveying the hydrated, enriched food material upwardly toward an upper end of the counter current extractor by means of the rotary screw conveyor whilst contacting the hydrated, enriched food material with the extracting liquid which is fed into the other end of the counter current extractor and flows downwardly under gravity to join the pool of enriching liquid; PA1 wherein the residence time of the food material in the pool enriching liquid is essentially no longer than the time taken to hydrate the dried food material.

The present invention relates to an improved method of counter current 
extraction of soluble components from a solid. 
U.S. Ser. No. 08/185,794, ("the parent specification") reveals an improved 
method of counter current extraction in which there is provided a process 
for extraction of a soluble component from a food material which process 
includes: 
providing: 
a food material to be extracted, 
an extracting liquid, and 
an enriching solution of the soluble component to be extracted; 
contacting the food material and enriching solution to obtain an enriched 
food material; and 
contacting the enriched food material with the extracting liquid in 
counter-current flow. 
In that invention, the counter current extraction takes place in a counter 
current extractor including a rotary screw conveyor mounted within an 
inclined or vertical elongate housing having an upper end and a lower end 
such that food material is fed into a lower end of the housing to contact 
the enriching solution which forms a pool at the lower end of the housing, 
the food material then being carried upward by the rotating screw in 
counter-current to the extracting liquid which is fed into an upper end of 
the housing and flows downward under gravity. 
It has now been found that a further step in the process leads to an 
improvement in the end product of the extraction process when extracting a 
dried food material according to this embodiment of the parent 
specification. 
According to a first aspect of the present invention, there is provided a 
process for extraction of a soluble component from a dried food material, 
which process includes; 
providing: 
a dried food material to be extracted, 
an extracting liquid, and 
an enriching liquid consisting essentially of a solution of the soluble 
component to be extracted; 
forming a pool of enriching liquid at a lower end of a counter current 
extractor including a rotary screw conveyor mounted within an inclined or 
vertical housing; 
feeding the dried food material into the lower end of the counter current 
extractor to contact the pool of enriching liquid wherein enriching liquid 
is absorbed by the dried food material to form a hydrated, enriched food 
material; 
conveying the hydrated, enriched food material upwardly toward an upper end 
of the counter current extractor by means of the rotary screw conveyor 
whilst contacting the hydrated, enriched food material with the extracting 
liquid which is fed into the upper end of the counter current extractor 
and flows downwardly under gravity to join the pool of enriching liquid; 
wherein the residence time of the food material in the pool of enriching 
liquid is essentially no longer than the time taken to hydrate the dried 
food material. 
The dried food material is preferably one in which cell walls are no longer 
intact or organised. The food material may be subjected to a crushing or 
grinding step. Particularly preferred food materials are coffee, tea, 
tobacco, almond hulls, vanilla and other dried flavour and fragrance 
materials. By "dried", it is meant that the liquid content of the food 
material has been reduced, either by heating, pressing, vaccuum drying or 
any other means. 
The extracting liquid is preferably water. 
The concentration of said soluble component in the enriching solution is 
preferably greater than that which can be achieved in the extracting 
liquid when extraction with the extracting liquid is carried out without 
first contacting the food material with the enriching solution. 
It is particularly preferred that the concentration of said soluble 
material in the enriching solution is greater than the concentration of 
the soluble component in the unextracted food material. Thus the enriching 
solution may be an aqueous solution in which the soluble component is at a 
greater concentration than it is in the unextracted food material. 
The counter current extractor used in accordance with the invention may be 
of the type described in Australian Patent No. 543184. Preferably the 
reversal of the screw conveyor occurs less than every 20 seconds and 
preferably less than every 15 seconds. 
The liquid extract discharged from a counter current extractor may be 
diverted through an independent heat exchanger and recirculated. 
Preferably the recycle is taken from a pool of concentrated solution. 
It is particularly preferred that the concentration of the pool is greater 
than the discharge soluble component concentration which may be achieved 
by operating the extractor under the same conditions without enrichment. 
For example, where coffee is being extracted the pool of concentrated 
solution may be established by the addition of a concentrate which may for 
example be a dried and ground coffee beans, more preferably a freeze dried 
coffee, or other coffee product commonly referred to as instant coffee, 
which may be in the form of a concentrated solution. By a single addition 
of instant coffee to achieve a concentration in the pool of at least 
25.degree. Brix and preferably at least 30.degree. Brix further extraction 
occurs enabling liquid having a concentration over 20.degree. Brix to be 
continuously achieved. Under conventional techniques it is generally not 
possible to achieve a concentration of over about 15.degree. Brix by 
extracting with water. The limit for counter current extraction without 
enrichment is about 20.degree. Brix. 
It is generally preferred that the extractor is provided with means for 
ensuring a predetermined extracting liquid level in the lower region of 
the housing. Preferably the recycled extracting liquid is taken 
continuously from a pool of liquid established at the bottom of the 
machine. 
In a preferred embodiment said soluble component is added to said pool of 
enriching liquid and fresh extraction liquid is continuously introduced. 
Preferably the concentration of said soluble component in the pool of 
enriching liquid is greater than the concentration which may be achieved 
using the extracting liquid under the same conditions. 
The time necessary to hydrate the dried food material, and hence the 
residence time in the pool of enriching liquid is dependant upon many 
factors, including the type of food material, the extent to which the food 
material has been crushed or ground and the degree of drying which has 
occurred. For some food materials, such as coffee, the type or blend of 
coffee can also be a factor. Whilst some dried food materials require 
considerably longer hydration periods, generally it has been found that 30 
minutes is sufficient time to hydrate the dried food material. Preferably, 
the hydration time is 15 minutes. 
It is preferred that the temperature of the extracting liquid is in the 
range of from approximately 50.degree. C. to 80.degree. C. although higher 
or lower temperatures may be used if desired. 
We have found that there is a significant improvement in the efficiency of 
extraction, particularly for coffee, when using the method of the 
invention at a temperature of at least approximately 50.degree. C. 
The efficiency of extraction is also determined to some extent by the ratio 
of the inputs of fresh extracting liquid feed and solid fees. Preferably 
the ratio of liquid feed to solid feed is in the range of from 
approximately 1:10 to 10:1. 
A more preferred ratio, particularly when the solid hydrates to some extent 
such as in the use of coffee, is in the range of from approximately 1:1 to 
5:1. A ratio of about 3:1 has been found to be particularly suitable for 
coffee. 
Generally it is preferred where liquid is recycled that the recycle rate is 
greater than half the liquid feed rate and preferably at least the same as 
the feed rate. Most preferably the recycle is at least twice the liquid 
feed rate. The product produced by the process of the present invention is 
an enriched feed. 
Whilst not wishing to be bound to a particular theory of operation, it is 
believed that simultaneously with the uptake of liquid, soluble coffee is 
being released into the pool liquid. (Because the coffee is both dried and 
ground then at the point of entry it is to be expected that some coffee 
will be extracted). 
Provided that the residence time of the ground coffee in the pool is not 
substantially larger than the time during which liquid is being absorbed 
(the wetting time) then there will be no tendency for the concentration of 
solubles in the bean and in the coffee extract entering the pool to 
equilibrate. Because they have not equilibrated, the difference in 
concentration between the solubles in the extraction liquid and the 
solubles in the bean provide the driving force for mass transfer in the 
section above the pool where the 2 phases are truly flowing counter 
current. 
If ground coffee is extracted using water as a solvent then the dried 
coffee beans will absorb twice their own weight of water so that each 100 
gms of beans containing 25 gms of soluble coffee will absorb 200 gms of 
water. Therefore, at start up the concentration of soluble coffee in the 
liquid phase of the hydrated bean will be 12.5%. 
As the extraction process proceeds, dried coffee entering the CCE will 
absorb extract of increasing concentration and hence will in turn provide 
an extract of increasing concentration until an equilibrium is 
established. This equilibrium would be expected to be around 
12.degree.-15.degree. Brix (12-15%) and this is borne out by commercial 
experience when using both the continuous screw conveyor and batch-type. 
If a pool of concentrated coffee extract, say at 25.degree. Brix, is 
established at the lower end of a continuous screw conveyor extractor at 
start up and the same operating conditions are maintained in terms of 
coffee feed rate and extraction water feed rate then it would reasonably 
be expected that at start up the extract would be at 25.degree. Brix and 
this concentration would fall to 12.5% over time. Surprisingly this is not 
the case. 
The very high concentration of the extract from the present extraction 
process allows the elimination of a preconcentrations step using 
evaporators (12.degree. Brix to 40.degree. Brix) before spray drying or 
freeze drying. Thus, a dried product with a significantly higher content 
of aroma compounds normally lost during evaporation may be produced.

As seen in FIG. 1 the counter current extractor 10 comprises an elongate 
trough shaped housing 11 in which is disposed a screw conveyor 12 which is 
arranged to be rotated about its longitudinal axis by drive means 13. The 
housing 11 is provided with an inlet hopper 14 for the introduction of 
material to be extracted. The hopper 14 is disposed above the lower end of 
the screw which is inclined slightly upwardly towards an outlet spout 15 
for the solid material which has been treated. A discharge line 16 is 
provided for the discharge of the extracting liquid which is charged into 
the housing 11 through charging line 17. A heat exchanger 18 is provided 
on a bypass line 19 to heat discharged liquid and to return it through 
nozzle 21 to the lower end of the housing 11 to heat the material being 
treated. 
Under operating conditions disclosed in Australian Patent No. 543 184 food 
material is introduced to the hopper 14 and passes into the lower end of 
the extractor 10 and is carried by a single screw 12 toward outlet spout 
15 where extracted material is deposited. Extracting liquid is introduced 
through the charging line 17 and flows under gravity toward the end 
adjacent the hopper 14. 
A pool of extracting liquid 23 containing extracted soluble material is 
maintained at a constant level 23 by drawing off liquid extract. A portion 
of the liquid extract is recycled via recycle line 19, a heat exchanger 18 
and reintroduced through nozzle 21. 
When operating using coffee as the food material the extractor may be 
provided with a heated jacket at about 90.degree. C. to provide an 
extracting liquid temperature of about 50.degree. C. 
Under such conditions a steady-state is achieved where a pool concentration 
of about 12.degree.-15.degree. Brix is provided. 
In a counter current solid-liquid extractor the concentration of solubles 
in both the solid and liquid phases will reach a steady-state. 
At steady-state the concentration of solubles in the solid phase will 
exceed the concentration in the liquid phase. This concentration 
difference provides the driving force to transfer the solubles from the 
solid to the liquid. 
Typical concentration profiles for the solid and liquid phases are shown in 
FIG. 2 where C.sub.s represents a typical concentration profile of solute 
in the solid phase, C.sub.l represents a typical concentration of solute 
in the liquid phase, and C.sub.l ' represents a changed concentration 
profile in the liquid phase brought about by artificially lifting C.sub.s 
by enrichment at the point of entry of the solid phase of the machine in 
accordance with the method of the invention. These concentration profiles 
reflect the laws governing diffusion and mass transfer. For diffusion the 
material diffused (dm) is determined by the relationship 
EQU dm=qDAdt(dc/d.sub.x), 
the mass transfer ds is provided by the relationship 
EQU ds=kAdt(C.sub.s -C.sub.l). 
It is to be expected that if a concentration of solubles in the liquid 
phase 4 was induced to exceed the concentration of solubles in the solid 
phase, then a condition is established whereby solubles will transfer from 
the liquid phase back into the solid phase. 
In the present invention however when the concentration of solubles in the 
liquid phase at point A in FIG. 1 is raised above the proportion of 
solubles in the solid phase as a percentage of total weight (for example 
by addition of a concentrate to the lower end of the machine) surprisingly 
then that induced high concentration can be maintained or increased even 
though fresh extracting solvent is introduced. 
The waste therefore remains low and dilution is reduced as shown in FIG. 2 
by comparison of C.sub.l and C.sub.l ' profiles. 
In FIG. 3, the net effect of the pool only is to concentrate the extract 
entering the pool from 33% soluble solids to the extract leaving the pool 
at 40% and to enrich the soluble solids content of the dried coffee from 
25% to 52% of total dried weight and add 120% of water, (ie. 120 g water 
to 100 g dried coffee). As the hydrated bean emerges from the pool, the 
entrained liquid contains 40% soluble solids. The bean then enters the 
portion of the extractor providing true counterflow at this enriched level 
of soluble solids and the soluble solids are then extracted in accordance 
with normal diffusion principals, resulting in an extract at significantly 
higher concentration than from a bean which has not been enriched. In FIG. 
4, the effect of the pool only is to concentrate the extract entering the 
pool from 13% to extract leaving the pool at 20% and to enrich the soluble 
solids content of the dried coffee from 25% to 35% of total dried weight 
and add 160% of water, (ie. 160 g water to 100 g dried coffee). Again the 
bean is enriched upon leaving the pool, resulting in higher concentration 
extracts. 
To achieve these results, the residence time of the ground coffee in the 
pool is kept to less than the hydration time. This is done by controlling 
the level of the pool, as well as conveyor screw speed, time of forward 
motion and time of reverse motion of the screw. The use of a rotary screw 
conveyor counter current extractor is an integral part of this process, as 
it allows the necessary degree of control over the hydration time in the 
pool. A further advantage of the process is that it allows simple control 
of the concentration of the end product extract simply by changing the 
concentration of the enriching liquid in the pool at start up. 
It is to be understood that various other modifications and/or alterations 
may be made without departing from the spirit of the present invention as 
outlined above.