Process of extracting stimulants from coffee

A method of producing coffee low in undesired stimulants by removing coffee wax from unroasted coffee by the use of a supercritical fluid and absorbing the coffee wax in an absorbent precharged with pure caffeine.

Apart from the stimulating effect of caffeine on heart activity, other 
ingredients of roasted coffee beans can have a harmful physiological 
effect on the gastrointestinal system. 
These undesired stimulants are predominantly lipophile substances which 
appear in so-called coffee wax and coffee oil [cf. W. Kiekebusch et al, 
Arzneimittelforschung, vol. 14. (1964), p. 1249; G. Czok et al, 
Arzneimittelforschung, vol. 12 (1962), p. 1195; U. Harms et al, 
Zeitschrift fur Lebensmitteluntersuchung und -forschung, vol. 138 (1968), 
p. 75; U. Harms et al, KTM, vol. 19 (1969), No. 6, pp. 6-9, No. 7, pp. 
6-9] and are partially carried over into the coffee during ordinary 
brewing. 
It is known that the digestibility of coffee can be significantly improved 
by removing the coffee wax ingredients from raw coffee [S. Gal: 
Lebensmittel und Ernahrung 27, pp. 218-220, 235-237 (1974)]. 
Carboxylic acid-5-hydroxytryptamides (C-5-HT) found in coffee wax serve as 
indicators of successful removal of these substances which form so-called 
roasting stimulants after roasting [J. Wurziger, 5. ASIC Colloquium, 
Lisbon (1971) "Carboxylic Acid Hydroxytryptamides for Evaluation of Fresh 
and Processed Coffee"]. 
In 1973 the Federal Health Office in Berne decided to classify any coffee 
demonstrably having a C-5-HT content of less than 400 ppm as a weak 
stimulant. With the decrease of C-5-HT content, the digestibility of 
coffee increases. 
It is therefore the object of the present invention to produce a coffee low 
in undesired stimulants and to stay as far as possible below the 
aforementioned limit without altering the caffeine content of the raw 
coffee. 
German Pat. No. 576,515 discloses a refining process in which raw beans are 
treated with pressurized steam. This is intended to improve the flavor and 
digestibility. In the refining method of German Published Application No. 
1,692,284, stimulants are extracted from raw beans by a one minute 
treatment with liquid CO.sub.2. However, these processes hardly remove any 
of the coffee wax constituents. 
For this reason, later processes, e.g., those of German Published 
Applications Nos. 1,960,694 and 2,031,830, turned to treatment with 
organic solvents. The raw coffee beans are washed directly with methylene 
chloride, 1, 2-dichloroethane or trichloroethylene while being heated, 
without prior decomposition by water or steam. After evaporation of the 
solvent the beans are dried. By this process C-5-HT values between 90 to 
230 ppm are obtained. 
Most recently, the coffee industry has preferred processes which employ no 
liquid organic solvents, e.g., the quantitative extraction of caffeine 
from raw beans with the aid of moist supercritical CO.sub.2 (German Pat. 
No. 2,005,293). 
Surprisingly, it has now been discovered that coffee wax and the carboxylic 
acid-5-hydroxytryptamide contained therein can be successfully eliminated 
with the aid of supercritical gases, the coffee wax absorbed by the 
super-critical gas being continuously and selectively removed therefrom. 
An object of the invention is a process for producing coffee low in 
roasting stimulants by removal of coffee wax from unroasted coffee beans 
while retaining the original caffeine content, the coffee beans being 
treated with a harmless solvent comprising supercritical fluid. 
By "supercritical fluid" is meant a gas which is above its critical 
temperature and pressure. 
The water content of the raw coffee can be set at 2 to 60% by an 
appropriate method of drying, steaming or spraying the preheated coffee 
beans with liquid water before removal of the undesired stimulants. The 
preferred moisture content is from 20 to 35%. 
Gases or gas mixtures whose critical temperature is in the area of up to 
ca. 100.degree. C., e.g., CO.sub.2, SF.sub.6, N.sub.2 O and, optionally, 
halogen-containing hydrocarbons with 1 to 4 carbon atoms, e.g., CHF.sub.3, 
CHF.sub.2 Cl, CF.sub.3 Cl, CF.sub.2 =CH.sub.2, C.sub.3 F.sub.8, C.sub.2 
H.sub.6, C.sub.3 H.sub.8, C.sub.2 H.sub.4, and C.sub.3 H.sub.6 can be used 
for producing the supercritical fluid. 
According to a further feature of the invention, an entrainer can be added. 
Since the solubility of the wax in the supercritical fluid is relatively 
low, its solubility in the circulating supercritical fluid can be enhanced 
by the addition of an entrainer. Entrainers alter the steam pressure and 
consequently the dispersion conditions of low volatility substances in the 
circulating fluid phases by increasing the separation factor in a 
favorable way (German Published Application No. 2,340,566), so that under 
the existing steam pressure conditions the coffee wax is removed more 
rapidly from the raw coffee. 
According to the invention the entrainer or entrainer mixture must be so 
chosen that the selectivity of the circulating supercritical fluid for the 
coffee wax is increased as much as possible and is dependent on the 
selected separation pressure and the temperature. Its concentration 
depends on its miscibility. 
If the mutual miscibility with the circulating supercritical fluid phase is 
incomplete, the concentration corresponds maximally to the saturation; if 
it is complete, the concentration amounts to 0.001 to 10% by weight. The 
entrainer can be introduced into the cycle at any desired point, with the 
aid of a dosing pump (6 in FIG. 1), or by impregnating the adsorbent with 
the entrainer or by bubbling the supercritical fluid through an entrainer 
supply. 
Natural constituents of raw and roasted coffee are especially suitable as 
entrainers, e.g., alcohols (methanol, ethanol), ethers (diethyl ether), 
ketones (acetone, butanone-2), esters (ethyl acetate and ethyl formate), 
as well as halocarbons (methylene chloride, trichloromonofluoromethane), 
aromatics (toluene) and aliphatic compounds (n-hexane). 
A particular advantage of this process is the fact that the entrainer 
residues are already removed during removal of the coffee from the 
supercritical fluid to such an extent that subsequent evaporation of the 
dewaxed raw coffee beans can be either omitted or, as opposed to prior 
processes, significantly abridged. Drying can be carried out in the 
customary manner in a drum dryer or other drying apparatus. 
The working temperature of the process is above the critical temperature of 
the gas or gas mixture used, e.g., up to 150.degree. C. above the critical 
temperature, preferably between 40.degree. to 100.degree. C. above the 
critical value. 
The working pressure of the process depends on the desired processing time 
and can be between the extremes of 20 to 800 bar, these limits being 
chosen for practical reasons. 
The speed of flow, and with it the circulating volume of the supercritical 
fluid, depends on other parameters of the process, such as pressure, 
temperature, kind of supercritical fluid, entrainer and adsorbent as well 
as processing time, which can run from 0.5 to 50 hours. 
The carboxylic acid-5-hydroxytryptamide and the coffee wax can be removed 
from the circulating supercritical fluid with the help of an adsorbent 
pre-charged with caffeine (see FIG. 1). All known sorption agents, 
especially active carbon, can be considered for the adsorption of 
separated wax particles from the circulating supercritical fluid. 
Pre-charging of the sorption agent with caffeine is preferably attained by 
contacting the sorption agent with an aqueous pure caffeine solution at a 
temperature of 20 to 150.degree. C. and a pressure of 1 to 10 bar. The 
contact can occur, e.g., in a stirrer or by passing the aqueous pure 
caffeine solution through an amount of sorption agent. Finally, the 
sorption agent is dried by a known drying process until the desired final 
water content is obtained. 
The caffeine content of the pre-charged sorption agent is to be so selected 
that a dynamic equilibrium of caffeine concentrations results between raw 
coffee, supercritical phase and sorption agent, so that the caffeine 
content of the raw coffee remains unchanged. 
The water content of the pre-charged sorption agent is to be so selected 
that the water content of the moist raw coffee does not go below a 
predetermined minimum during processing, so that there is no change in the 
bulk weight of the coffee beans during removal of the raw coffee from the 
supercritical phase. The preferred minimum water content is above 15% by 
weight. 
According to the invention, the mass ratio of the raw coffee and the 
sorption agent must be so selected that all the removed stimulants are 
completely adsorbed. 
The separation of the wax constituents and the C-5-HT contained therein 
from the sorption agent can be carried out according to well-known methods 
of sorption agent regeneration, preferably with an organic solvent, with 
subsequent removal of the residual solvent by evaporation and drying. 
Instead of adsorption of the wax particles and contained C-5-HT dissolved 
in the supercritical fluid, these substances can also be separated by 
altering the pressure and/or temperature. This variant process (see FIG. 
2) requires a supercritical fluid with a particularly high degree of 
selectivity for coffee waxes in order to avoid a concurrent drop in the 
caffeine and water contents of the raw coffee beans. 
As an alternative, balance in caffeine content can also be achieved by 
introducing a caffeine solution into the circulating supercritical fluid, 
e.g., with a dosing pump (6 in FIG. 2), thereby avoiding any change in the 
caffeine content of the raw coffee beans. 
The process according to the invention produces a coffee low in undesired 
stimulants whose C-5-HT content can be diminished to below 200 ppm while 
the initial caffeine content remains unchanged. The process can be so 
carried out that the raw coffee beans, low in stimulants, contain no 
traces of solvent and, without subsequent steaming, can immediately be 
dried in the drum in the customary way. Subsequently, the beans can be 
roasted in the usual way. The result is a roasted coffee whose appearance 
and taste are indistinguishable from the finest natural mild blends. 
FIG. 1 shows an apparatus for continuous removal of undesired stimulants 
from raw coffee by means of a supercritical fluid. Extractor 1 contains an 
amount of raw coffee beans whose water content is brought to a 
predetermined value before they enter the extractor. The fluid is passed 
from storage vessel 8 into the extraction cycle. Circulating pump 3 
maintains circulation of the fluid in the extraction cycle, which 
comprises the extractor 1, an adsorber 2 and a heater 5. The adsorber 
contains an adsorbent pre-charged with pure caffeine and/or entrainer. The 
heater 5 heats the circulating fluid to the processing temperature which 
is above the critical temperature of the fluid. 
Dosing pump 6 serves for introducing the entrainer and/or caffeine solution 
into the cycle. After heating, the supercritical fluid continuously flow 
through extractor 1 where it becomes charged with the coffee wax and 
C-5-HT contained therein. In turn, these substances are removed from the 
circulating fluid in adsorber 2. By suitable pre-charging of the adsorbent 
with pure caffeine, or by dosing of a sufficient amount of caffeine 
solution through dosing pump 6, the caffeine and water contents of the 
supercritical fluid flowing to extractor 1 are always set in such a way 
that the extractor removes no caffeine or water, but only coffee wax, from 
the raw coffee beans. 
Another possible way of separating coffee wax from the circulating 
supercritical fluid is shown in FIG. 2. This method is characterized by 
cooling the supercritical fluid below its critical temperature in cooler 7 
after it leaves extractor 1. This alters its dissolving characteristics so 
that a separate phase comprising a mixture of coffee wax, caffeine and 
water forms in the subcritical fluid and can be separated therefrom in a 
separator 4. If an entrainer is used, this also will be removed in 
separator 4. After reheating the fluid to supercritical temperature in the 
heater 5, enough caffeine solution is injected into the fluid by dosing 
pump 6 to ensure the same caffeine, water and entrainer contents of the 
fluid flowing to extractor 1 as before separation of the coffee wax. 
Subsequently, the extractor removes only coffee wax from the raw beans, 
not caffeine and water.

The process is illustrated by means of the following examples and 
accompanying drawings. 
EXAMPLE 1 
In an apparatus according to FIG. 1, 30 kg raw coffee having a moisture 
content of 33% by weight was processed for 4 hours at 80.degree. C. and 
under 250 bar pressure with moist supercritical CO.sub.2, the moist raw 
coffee being present as a solid mass in extractor 1. Active carbon, 
charged with aqueous, saturated caffeine solution, was used as adsorbent 
and was brought to a water content of 16% by weight by subsequent drying. 
The adsorbent was present in adsorber 2 as a solid mass. After filling the 
system with CO.sub.2 from the storage vessel 8, the CO.sub.2 was 
circulated by circulating pump 3 and heated to the desired supercritical 
temperature in heater 5. The filling amount of CO.sub.2 was so chosen as 
to ensure the desired pressure after heating of the CO.sub.2. The 
circulating mass stream of supercritical CO.sub.2 weighed 150 times as 
much as the raw coffee. The processed raw coffee was dried in a vacuum 
drum dryer at 75.degree. C. and 0.2 bar pressure. Finally, the coffee was 
roasted in a conventional drum roaster. 
The analytical results after drying and roasting are shown in Table 1. 
TABLE 1 
______________________________________ 
Analytical Results for Example 1 
Roasted Coffee 
Material Unprocessed Processed 
______________________________________ 
C-5-HT, ppm 580 160 
caffeine, % 1.11 1.18 
water soluble 
substances, % 26.4 26.7 
______________________________________ 
EXAMPLE 2 
In an apparatus according to FIG. 1, 30 kg raw coffee with moisture content 
of 10.5% was processed for 6 hours at 70.degree. C. and under 300 bar 
pressure with dry supercritical CO.sub.2. The raw coffee was present in 
extractor 1, and active carbon, previously impregnated with 2.4% by weight 
acetone, was used as adsorbent in adsorber 2. After filling the apparatus 
with CO.sub.2, the gas was circulated and brought to the aforementioned 
supercritical conditions. After processing, the CO.sub.2 was removed from 
the system in such manner that no change occurred in the bulk weight of 
the raw coffee. The coffee was roasted immediately after removal. 
TABLE 2 
______________________________________ 
Analytical Results for Example 2 
Roasted Coffee 
Material Unprocessed Processed 
______________________________________ 
C-5-HT, ppm 640 130 
caffeine, % 1.14 1.16 
water soluble 
substances, % 26.3 26.7 
______________________________________ 
EXAMPLE 3 
In an apparatus according to FIG. 2, 30 kg raw coffee with a moisture 
content of 45% by weight was processed for 8 hours at 90.degree. C. and 
under 200 bar pressure with moist supercritical CO.sub.2, the moist raw 
coffee being present in extractor 1. The circulating CO.sub.2 was cooled 
from 90.degree. C. to 25.degree. C. in cooler 7 and thereby liquefied. A 
mixture of coffee wax, caffeine, and water was continuously obtained as a 
separate phase in separator 4 from the liquid CO.sub.2 and withdrawn from 
the separator. An aqueous caffeine solution, whose amount and caffeine 
content corresponded to the water and caffeine amount removed in separator 
4, was continuously added by means of dosing pump 6 to the supercritical 
fluid heated in heater 5 to the supercritical temperature 90.degree. C. 
Drying and roasting followed as in Example 1. The analytical results 
obtained after roasting are shown in Table 3. 
TABLE 3 
______________________________________ 
Analytical Results for Example 3 
Roasted Coffee 
Material Unprocessed Processed 
______________________________________ 
C-5-HT, ppm 620 175 
caffeine, % 1.42 1.45 
water soluble 
substances, % 26.5 26.1 
______________________________________