CA1084330A - Method of making a coffee extract - Google Patents

Abstract

A METHOD OF MAKING A COFFEE EXTRACT
Abstract of the Disclosure An improved coffee extract is prepared by subjecting roast and finely ground coffee particles of 5-800 microns to a slurry extraction operation which employs moderate temperatures and low shear gentle agitation to negotiate the extraction of high quality soluble coffee solids there-from without forming emulsions caused by released coffee oils and excessive agitation. The extract is separated from slurry insolubles to yield 18% - 27% soluble coffee solids based on the dry weight of the roast and ground coffee charge. This extract provides the basis for an improved instant coffee.

Description

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Background of_the Invention This invention relates to a slurry extraction pro-cess for preparing a coffee product.
Many methods have been described for the production of coffee extracts. For the most part, these methods have been aimed toward the provision of coffee products capable of duplica-ting the desired flavor qualities of freshly brewed roast and ground coffee. Illustrative of such methods are those described in U.S. Patents Ponzoni, 3,261,689, July 1966; Gianturco et al.~ 3,164,474, January 5, 1965; Cascione, 3,532,507l October 1970; McSwiggin, -3,697,288l October 1972; Mahlmann, 3,244,532, April 1966;
and Pitchon et al., 3,653,910 and 3,655,399, April 4 and 11, 1~72.
While prior methods have utilized slurry extraction operationsl commercial processes for the most part have been based upon high temperature percolation methods and slurry extraction processes have been avoided because of poor yields, poor quality or processing problems. - -It is an object of the present invention to provide an improved slurry extraction process to produce a high quality coffee extract.
Summary of the Invention It has been discovered that a soluble coffee extract having preferred flavour attributes of freshly brewed roast and ground coffee without certain undesirable and character~
istic bitter flavors can be realized in practical yield by resort to a slurry extraction process. In its essential aspects, the process of the present invention comprises forming an aqueous slurry of roast and finely ground coffee and from about 2 parts to about 10 parts of water by dry r~ _"
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33~ -weight of coffee, said slurry having a temperature of from ~bout 80F. to about 200F., said coffee having a particle size of from about 5 -to about 800 microns; and gently agitating the slurry so as to provide a substantially uniform suspension and an extract having a soluble coffee solids content of about 4% to abo~t 15%, said slurry being substantially emulsion-free, said gentle agitation being ' provided by a low shear system; and separating the aqueous extract from released coffee oil and slurry insolubles.
10 Description of the Preferred Embodlments , The process of the invention involves subjecting roast and ground coffee to a unique combination of processing -conditions for slurry extraction.
A blend of roasted coffee is first ground to a desired particle size ranging from about 5 to abo,ut 800 ' - microns. This grind size is critical for the gentle slurry extraction operation in the practice of the present invention and, thus, for the success of the production of the improved coffee extract.
Gentle agitation is required to avoid emulsification in the coffee extract of bitter-tasting coffee oils which are released from the fine coffee particles by excessive agitation. By mlnimizing the formation of emulsified coffee oils, the separation of a substantially emulsion-free extract of coffee solubles from the,~lurry insolubles is facilitated.
In general, coarse grinds tend to require excessive ~ -agitation and elevated temperatures to obtain practical' yields and consequently desired flavor characteristics are impaired. It has been found that the release of bitter-tasting coffee oils increases with the fineness of grind, .

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increased agitation and higher temperatures. The process of the invention makes use of finely ground roast and ground coffee ex-tracted under relatively mild extractive temp-eratures with gentle agitation. The fineness of coffee grind size, 5-800 microns, is critical in the present invention because the coffee particles can be suspended and extracted in practical yield under the gentle agi~ation conditions which avoid emulsification of bitter oils. The fineness also increases extraction yields because of in-creased contact with the slurry water. It also improves the quality of extract because the fineness perm1ts the use of lower temperatures, 80 - 200F.
An ultra-fine grind size of from about 10 to about 400 microns is preferred. A preferred way to get this grind size is by embrittlement of the roasted coffee beans with liquid nitrogen or liquid CO2 and then grinding the cold embrittled beans in a coffee grinder. A grinder suitable for this operation is the Fitz ~ Mill Model U Granulator manufactured by the ~itzpatrick Co., Elmhurst, Ill. 60126.
It will be noted that ultra-fine grinding of coffee is accomplished in this fashion without reaching temperatures that tend to degrade or drive off essential coffee volatiles; thus, enhancing the quality of the final coffee product. Preferably, the roast and ground coffee is ground at a temperature of abou'c -110F to about -320F.
After the blend of coffee beans is roasted and ground, it may be suhjected to a steam-stripping or de-volatilization operation. However, care should be taken not to degrade the coffee flavors and aromas in the vola-tiles as well as those in the soluble coffee solids. This operation is, however, preferred. A suitable steam-stripping ~:1 .... . .

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process is described in Example 1 herein and more fully described in Gregg, co-pending Canadian application, Serial No. 270,673, filed January 28, 1977.

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~n aqueous slurry comprising the rclast and gro~nd coffee and f~om abo~ 2 parts to about 10 pa~ts of water by weight of the dry coffee is prepared. The slurry extraction is conducted at a temperature of from about 80E~ to about 200F for about 3 to about 120 minutes. Preferably, the slurry is heated by steam injections.
Preferably, the residence time of the coffee in the slurry operation is about 15 to 30 minutes, especially when the temperature of the slurry is about 90F to about 160F.
II coarser coffee particles of about 800 ~icrons are used, more time is required. The higher temperatures ~160-200F) can also be utilized to achieve the desired yields. However, what-ever the conditions are within the llmitations set out herein for the present slurry extraction operation, care must be taken lS to minimize the release of bitter-tasting coffee oil and the formation of emulsions while obtaining the aqueous c~ffee extract. When separated from the slurry insolubles, the aqueous coffee extract has a solids content of from about 4% to about 15%. It has been found that attempts to get aqueous extracts 2Q having original solids contents greater than about 15% seriously ..
compromise the quality of soluble coffee solids desired.
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That range, 4%-15%, represents extraction yields of about 18% to about 27% based on the dry weight of the coffee char~e.
It has been found in the practice of the present invention that excessive agitation will cause the release of excessive amour,ts of coffee oils from the S-800 - micron roast and ground coffee particles, and that this oil r ~ `' @~ i l l ~c cc~ u l s i i ~ ;e l ~ vc l ~; o ~ ~Ji ta tl on . Emu ~
sions in thc slurry cause separati.on pro~lems, e.g., by pl~lgging the ~ilter ~,~di~. The formation of thcse emulsions ~ust be avoicled. Accordi~ly, gentlc agitat:ion is employed, and as used herein, gentle agitation refers to a~itation sufficicntly high as to yermit the formation of a substantially ~niform slurry of cof~ee particles and an e~tract of coffee soluhles but sufficiently low as to provide an extract substantially free of emulsified coffee oils.
The aqueous extract is separated from the slurry insolubles by any appropriate method such as decantation, filtration or centrifugcltion. Preferred separation methods are those which assure that the separated coffee extract contains very little oil, e.g., no more than about 0.008 parts of cil per part o~
soluble coffee solids, and preferably no more than 0.004 parts of o11 per part o~ soluble coffee solids. A preferred method of -;~
separation is vacuum filtration. Vacuum filtration traps most of any re1eased coffee oil in the filter cake of coffee grounds formed on the filter media. Preferably, the cake o* coffee grounds is washed with water to rec~ver residual coffee solids and t~is wash water either recycled a~ slurry water or added to the coffee extract (filtrate). The filtrate, an aqueous cofFee extract having from about 4% to about 15% coffee solids, can be freeze-dried or spray-dried. Of course, the aqueous coffee extract

2~ is concentrated by conventional freeze concentration or evapo-ration techniques prior to drying. Where a soluble coffee ofthe instant type is desired, best results will be obtained by the employment of flavor add-back as a means of compensating for tbe loss of desirable volatiles incurred in drying. A
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preferred proccss for col.lecting desired volatiles for add- -back is described in E~ample I herein and in the afore~,enti.one~
co-pending appl ication oî Gregg.

Time, temperature, level of agitation and coffee-to-water ratio selected for the slurry extraction operation will depend to a large extent upon the grind size of the coffee particles treated. Tlle required time, heat and a~itation generally increases with grlnd size.
The agitation system used in the present inventi.on ~! 10 for the slurry extraction operation can be characterized as a low shear system. An example of such a system is a slow r.o~7ing i . (5-25 rpm) large leaf-shaped paddle, contoured to the veriical shape of a l.S ft. di~meter slurry extraction tank and clearin~
the`shell of the tank by about 1 to 2 centimeters. The speed, number of revolutions per minute, o~ the paddle is preferakly .
~ept to a minimurn, ~hat is,- a number high enough to main~ain a substantially uniform suspension of the coffee particles ~ut low enough as to not to cause emulsions in the slurry.
: . In the preferred process of the present invention, a slarry of devolatilized roast and ground cof~ee and water is fed into a continuous slurry tank and uniformly suspended therein. There i9 uniformity o~ slurry composition with time - and/or temperature. (Uniform as used herein means substantially uniform. ? A steady state of conditions are maintained so that the properties throughout the system do not vary with time.
The slurry flows continuously into t.he slurry extraction tank and the extract flows continuously out.

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It has been found in the practice of the present invention, that the water coffee ratio in the slurry extraction , ~-~8f~33~
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proces~ is preferab]y from abo~t 2:1 to ~bo~t 5:1 par~s by weight of said co~r~e and most pref~xabl~ f~om abo~t 2.25:1 to abou~ 3.0:1 parts by weis3ht of the said co~fee.
~ The coffee extract produced by ~he process of the present invention, ~hen diluted to beverage strensth, has been found to have a superior flavor, a ~lavor that is characteri~ed ~y mildness and unusual absence of harshness or bitterness.
The process of this invention will be furthcr u~der- 3 - stood by reference to the following E~amples:
EXAMPLE I
Six hundre~ pounds of a blend of green coffee beans were roasted in a Thermolo Roaster~ for 17.3 minutes at a ma~i-mum temperature of 420F. The roasted coffee had a photovolt ;~
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color of 72. The roaster was first preheated to 400F and the .
15 beans added thereto. ~ ~
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About 500 pounds (226.8 kg) of this roasted coffee ~ ~
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were cooled to embrittlement with liquid nitrogen and ~oLd fine ground coffee at a temperature of about -310F (-190Cj with a hammermill grinder to a particle size ranging from : .
20 about lO to about 75 microns. ~he~grinder used in this opera-~ion was a Fitæ Mill Model y Granulator/Comminutor, manufactured by the Fitzpatrick Co., Elmhurst~ Ill. 60126, and described in its Bulletin No. 202. ~ 33 mil screen and DS-675 blades were used, both of which are Fitz Mill products. The ground coffee 25 was held overnight in a cold room at -40F ~-40C~

, DEVOLATILIZATION STEP
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The next day, these roast and ground coffee particles were fed into a mechanically fluidized bed ~provided b~ a 10.3 cubic foot continuous Littleford Mi~er, Model KM 300D, .

_~_ -manufactured by the Littleford sros. Inc., Cincinnati, ohio) at a flo-~ rate of 80 po~nds (36.29 kg) per hour.

Plo~-shaped mi~ing tools rotating at hi~h spe~ds insi~e the horizontal mixing shell lmparted rapid but gentle S` motion to the coffee paxti_~es, turnir.g them into a turb~lPrt fluidized state. The plows ~ere designed to lift the materi~ls from the drum ~alls so that rapid mixi~g takes place wJthout adverse effect on the ~ragile coffee particles.
The fluidized cofee paxticles ~-ere ~niformly wet 10 with about ~132 parts water per part of the coffee. The :
temperature of the water was about 65F (lg.33~ The water ~as di~persed into the mixing cha~ber ~drum) or the mlxer by spraying water onto choppers to obtain unlform wetting.
Independently dri~en rotating choppers arranged between the .
15 ~aths of the plows atomized the watex as we]l as bro~e up -~
-agglomerates or lumps which existed in the coffee bed :-hat - ~ may have formed during the operation. The water was sprayed ~
on the~coffee particles in the mixin~ chamber at a flow rate-of ~`

`about 10.5 pounds (4.76 kg) per hour.
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- A stream of cool steam was introduced into the bed or chamber counter-ourrent to the flow of the wet fluidized -- coffee particles, at a flow rate of about 2.3 pounds `(1.04 kg) - per hour. When the steam entered the vacuum chamber (the bed) its temperature fe:Ll to about 71F (21.67C~. Inside the mix-ing chamber was held under an absolute pressure of about 27 mm of mercury. The 1uidized bed temperature was about 71F.

Thes~ conditions were maintained throughout the operation with r little variation. The steam made intimate contact ~lith the : :

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3~33C3 coffee particles for about 1.2 minut:es and thereby stripped th~m of their volatiles. The prod~c:ts of this operation are called herein volatiies-laden steam and ~;et ~evolatilized coffee.
The volatiles-laden steam passed out of the mixing chamber through a gravity solids se~)arator to remove any carry--over o~ roast and ground coffee particles, and then collected and cond~nsed on the walls of a four-liter glass vacuum flask in the form of a frost. The vacuu~ flask was held under an abs~lute pressure of about 15 mm of mercury and at a temperature of about -320F (-195.56C) with a liquid nitrogen jacket and a vacuum pump.
~ boat 3.5 pounds (1.59 ~g) of ~he volatile laden-frost were recovered and the fxost ~as melted by contacting it with a~out 31.6 pounds (1~.33 ~g) of a 300/O solids, aqueous coffee e~ract.
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~ This volatile-laden extract was vacuum free~e-dried and yielded 6.6 pounds of substantiall~ d~y volatile-laden cof~ee granules ~hich were later mixed with a dry coffee ; ' extract (described below) to yield a final instant coffee -product. The fines obtained were recycled to the freeze-dryin~
operation.

, SLURRY EXTRACTION ST~P
~ The devolatilized coffee particles were conveyed out of the mixing chamber (of the ~ittleford Mixer) and mixed in a mixing tanX with an average of about ~.3 pounds (1.04 ~g).
of water per pound o~ coffee on a dry coffee weight basis. The resulting slurry was fed into a slurry e~traction tank at a r ~ j .

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flow rate o~ a~out 26~ pounds (119.75 kg) per ho~r. As the slurry w~s bein~ pump~d ~nto the slurry ~traction tank, it was heated to llO~F by steam injectio~
The slurry extraction tank used in this example ~/as s a 1.5 foot diameter stainless steel jacketed cone-bottom slurry tank equipped wiCh a large cone-tipped leaf paddle contoured to the cone bottom and shape of the slurry extracting tank and cleared the tanX shell by a~out 1 centimeter. The~large leaf shaped paddle provided thorough low~speed ~15 rpm) gentle 10 agitation for the slurry extraction operation.
- The gentle action o the leaf shaped paddle produced a substantially uniform suspension of finely ground coffee particles which extracted the coffee soLubles without releas-in~ an excessive amo~nt of bitter tasting coffee oils frorn the ` 15 coffee partic1e~s. ~o emu]sions wer~ observed in he slurry - itself on the filter media described helow.
` The volume of the slurry in the extraction tank was maintained at a constant by regulation of the slurry feed and output rates and the rates were such as to provide a residence 20 time for the average roast and ground coffee particle of about 20 minutes.
The slurry output was fed onto a rotating 10.5 sq. ft.
horizontal vacuum filter belt called the EIMC0-Extractor, manufactured by EIMC0, a subsidiary of the Ogden Corporation, ~5 Salt Lake City, Utah 84110. The eed flowed by gravity and was spread rapidly over the filtration deck by a full width arran~ement.

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The filtration cleck consisted of ~ synthctic fi]ter media, No. 887, and a traveling drainage belt. Vacuum ~fas a~7ied continuouslv through ports in the deck.
As the feed aispersed over the media, the combined forces of gravity and vacuum effected an almost immediate separation of the aqueous coffee e~tract from the feed and the coffee ground cake formed rapidly. It was observed that sorne coffee oil released during the sl~rry extraction operation was retained on the filter media and in the coffee ground cake.
No emulsion was observed. It is estimated that less than 0.00 parts of oil per part of soluble coffee solids passed into ~he I - separated aqueous extract. The aqueous ex~ract ~ lS drawm off through ~acuum ports to a holding tank.
The cake of coffee grounds was washed to remove lS residual coffee solubles and traveled to discharye. The wash water was recycled to a holding tank as slurry water and -~ixed with fresh devolatilized coffee. As the cake of coffee -- grounds rolle~d over a small diameter discharge roller the abrupt change in axiS broke the ca~ce loose and it fell away from the media. The media was washed clean before receiving fresh feed and this was discharged~
About 775 pounds (351.54 ~cg~ of extract were col-I lected, having a solids concentration of about 12.7 percent - ; and~an extraction yield of 98.75 pounds (44-79 kcJ) of solubles, about 19.75 percent based on the weight of the dry roast~and ground coffee charge. The aqueous extract was freeze-concentrated to about 39/O solids and vacuum free~e-dried into a ' .. : . . .
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soluble e~tract coff~e powder. The volatiles-la~len coffee granules of this example were blended with this extract coffee powder at an add-back level of about 19.2 percent to provide an excel].ent instant coffee.
When diluted to beverage strength, cup color was very clear and the flavor and taste superior to that obtained from a ~resh brew of vacuum coffee as judged by large panels of fresh brewed vacuum coffee users.
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, l~ Another coffee e~tract was obtained by the slurry I extraction procedure set out in Example I except that about 500 lbs. of fresh (undevolatilized) roast and ground coffee - of comparable particle size were used instead of devo].atilized roast a~d ground coffee.
- 15 ~ he aqueo~s coffee extra~t of this Exzmple, when diluted to beverage strength, was comparable to the flavor and taste;of the product of Example I.
When diluted to beverage strength~ cup color was very clear a~d the flavor and taste superior to that obtained from . ~
: 20 a fresh brew of vacuum coffee as judged by l.arge panels of fresh brewed vacuum coffee users.
¦ . h~lAT IS CLP~IMED IS:

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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for preparing a coffee extract from roast and ground coffee comprising the steps of:
(a) forming an aqueous slurry of roast and finely ground coffee and from about 2 parts to about 10 parts of water by dry weight of coffee, said slurry having a temperature of from about 80°F. to about 200°F., said coffee having a particle size of from about 5 to about 800 microns; and gently agitating the slurry so as to provide a substantially uniform sus-pension and an extract having a soluble coffee solids content of about 4% to about 15%, said slurry being substantially emulsion-free, said gentle agitation being provided by a low-shear system; and (b) separating the aqueous extract from released coffee oil and slurry insolubles.

2. The method of Claim 1 wherein said roast and ground coffee was ground at a temperature of about -110°F.
to about -320°F.

3. The method of Claim 1 wherein said roast and ground coffee has a slurry extraction residence time of about 3 to about 120 minutes.

4. The method of Claim 1 wherein said method is a continuous process.

5. The method of Claim 4 wherein said roast and ground coffee has an average particle size of from about 10 to about 400 microns.

6. The method of Claim 4 wherein said roast and ground coffee is devolatilized prior to said slurry extraction process.

7. The method of Claim 4 wherein the temprature of said slurry is between 90°F. and 160°F., and said roast and ground coffee has a slurry extraction residence time of about 15 to 30 minutes.

8. The method of Claim 4 wherein said slurry has a water : coffee ratio of from about 2:1 to about 5:1 parts by weight.

9. The method of Claim 8 wherein said coffee:water ratio is from about 2.25:1 to 3.0:1.

10. The method of Claim 1 wherein said separated aqueous extract has a coffee oil content of less than 0.008 parts per part of soluble solids.

11. The method of Claim 1 wherein said low shear agitation is provided by a paddle.