CA1042706A - Grinder gas fixation high pressure with reflux - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Coffee grinder gas is fixed in a glyceride at relative-ly high levels by contacting the components at high pressure within a vessel which is vented and refluxed through an overhead packed column and a partial condenser located above the column.

Description

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This invent1on relates to a method of manufacturing coffee aroma materlals.
This invention is related to commonly-assigned Patent Appllcation, lB2062 wherein is disclosed a method for condensing the aromatic gases given off during the comminution of freshly roasted coffee in a vertically-mounted, scraped-wall heat exchanger which is cooled by means of liquid nitrogen. The condensed gases are collected at the bottom of the heat exchanger in the form of a frost or snow and this frost is mixed with a 1~ liquid glyceride and then combined with a coffee extract prior to drying the extract (e.g. freeze drying) or combined with a soluble coffee powder.
Grinder gas, that is the gas which is released from roasted whole coffee beans when their internal cell structure is disrupted, such as during grinding of the beans and which also continues to be evolved from the disrupted and/or fractured bean for a short period thereafter, has long been recognized in the art as a higly desirable natural coffee aroma. The collec-tion and stabilzation of this aroma has, however~ proven to be a difficult undertaking, especially when it is desired for use in a commercial -sized soluble coffee system.
The use of grinder gas as a means to enhance the jar aroma of a soluble coffee powder is disclosed in United States Patent No. 3,021,218 to Clinton, et al. which aromatizes the jar headspace and United States Patent No. 2,306,061 to Johnston which condenses grJnder gas aromatics onto chilled soluble coffee powder.
The use of grinder gas condensates which are added to a liquid extract and dried in order to produce an improved cup aroma when the powder is dissolved in hot water is disclosed in United States Patent No 3,244,533 to Clinton, et al. which homogenizes coffee oil in extract and then adds condensed grinder gas aromatics.
Condensed grinder gas frost can be mixed with a liquid glyceride whi~h mixture is then processed to remove excess water, such as ~o4~70~
be centrifugation, prior to being combined with soluble coffee solids (e.g. soluble powder).
The addition of the condensed aromatics to a glyceride carrier is a known method for attempting to stabilizing the aromatics. Such glycerides as coffee oil, bland-tasting vegetable oils and triacetin have proven especially useful for this purpose; however other oils and low melting point fats may also be used. It has, however, been desired to maximize the amount of aromatics that are fixed in the glyceride carrier, since this would minimize aroma loss and would reduce the amount of the glyceride which would be incorporated with the soluble coffee product to obtain a desired amount of aromatization.
According to the invention there is provided a method for aromatizing soluble coffee with an aromatized glyceride comprising the steps of:
a) condensing, as a frost, an aroma-containing gas which has a high carbon dioxide content;
b) placing the aroma-containing frost in a pressure vessel, the amount of frost being sufficient to provide a saturated carbon dioxide phase within the vessel, and the pressure vessel being directly connected with an overhead packed column and a condenser located above the column;
c) isolating the vessel from the atmosphere;
d) supplying heat to the contents of the vessel to produce an internal temperature which is above the congeal point of the glyceride;

~ -2-1~)4Z7~6 e) contacting within said heated vessel the frost aromas and a liquid glyceride phase, said glyceride being present in the vessel at a level of about one gram of glyceride to 0.5 to 6 grams of the frost; thereafter, f) slowly releasing pressure from the vessel so that the glyceride is maintained in a liquid state;
g) refluxing the pressurized gas exiting the vessel by -2a-means of the condenser and then h~ combining the aromatized glyceride with coffee solids.
Thus this invention is directed to fixing in a glyceride carrier aromatics contained in an aroma-bearing gas which has a high (e.g., above 80% by weight) carbon dioxide content, and which gas has been condensed as an aroma-bearing frost. This invention is particularly described in terms of coffee grinder gas, which is in excess of 90% by weight CO2; however, it is to be understood that other aroma-bearing gases which have a high carbon dioxide content such as coffee percolator vent gas and coffee roaster gas, may likewise be employed and are con-sidered to be within the scope of this invention.
The process of this invention employs high pressure together with reflux as a means to increase absorption of the volatile compounds present in an aroma-bearing carbon dioxide frost by a glyceride carrier. The process, which may be conduct-ed as a simple batch operation in a suitable pressure vessel, or as a semi-continuous, countercurrent operation in a battery of pressure vessels, eliminates the need for laborious mixing of the frost and the glyceride. This mixing operation has proven to be troublesome in commercial operation, since contact between the condensed frost and the glyceride quickly congeals the gly-ceride thus making uniform mixing of the two components quite difficult.
Contacting the gaseous frost and a liquid glyceride phase within an isolated pressure vessel has proven to be a desi-rable method to increase the level of aromatics fixed in the glyceride; however, the end temperatures and pressures (e.g., ~ _ 3 _ 7(~;
70F. and 855 psig.) permit the presence of liquid carbon dioxide. Conditions which permit the presence of liquid CO2 within the pressure vessel also allows some of the - 3(a) -~ 7~)~
aromatics to be dissolved in the liquid CO2 phase accordin~ to equilibrium partition conditions based on complex relationships between vapor pressures, solubilities, and chemical potential.
When a pressure vessel containing an aroma-bearing liquid C02 phase is vented, nearly all of the desirable organic materials dissolved in the liquid CO2 will co-distill and be lost in the vent gas.
The invention describes a process wherein the pressure vessel is directly connected, such as through an open vent, with an overhead packed column and a partial condenser located above the column. A pressure or gas flow regulator will be located upstream from the condenser and will usually serve as the means for isolating the pressure vessel from the atmosphere. Thus, instead of venting the pressure vessel directly into the atmosphere where the aromatics will be lost, the boiling CO2 passes through a packed column in which liquid C2 is refluxing from the partial condenser. Contact in the column between the gaseous C02 and the refluxing liquid CO2 enriches the liquid phase in aromatics. As the concentration of aromatics increases in the liquid CO2 phase within the pressure vessel, at least a portion of these aromatics will pass into the liquid glyceride phase. Thus, by this technique, a higher level of aromatics can be fixed within the glyceride.
According to the invention, a quantity of an aroma-bearing carbon dioxide frost, which may be obtained from a liquid nitrogen-cooled, scraped-surface heat exchanger, is contacted in a pressure vessel with a liquid glyceride phase at ~ 0 4'~7 ~ 6 a ratio of grams of frost to grams of glyceride of about 0.5:1 to 6:1. The vessel is isolated from the atmosphere and the vessel contents are continuously supplied with heat by such means as a water jacket. Heat is supplied in sufficient quantities to raise or maintain the temperature of the gly-ceride above its congeal point, preferably the contents of the pressure vessel will reach at least room temperature. As the temperature of the frost increases, a gaseous phase on increasing pressure is developed and as the temperature increases above about -69.9F, the remaining condensed carbon dioxide is converted from a solid phase to a liquid phase. As the temperature of the vessel contents exceeds the congeal point of the glyceride, the aromatics will readily dissolve in the liquid glyceride phase. It may be desirable to hold the vessel contents at a particular temperature above the congeal point of the glyceride in order to lengthen by an hour or more the contact time between the liquid glyceride and the aromatics.
Agitation of the vessel contents, such as by means of an internal stirrer, may also be desirable in order to increase absorption of aromatics by the liquid glyceride phase.
The frost and the glyceride may be placed in the vessel at the same time (i.e. before any heat is supplied to the vessel), or the frost may be permitted to warm within the vessel, say to a temperature above the congeal point of the glyceride, before the glyceride i5 placed within the vessel.
After the frost and glyceride within the vessel reach the desired temperature, preferably about room temperature, and possibly after a hold-up period, the pressure within the vessel ~ 042706 is slowly, preferably isothermally, released. Slow pressure release is desirable in order to prevent the temperature of the vessel contents from dropping below ~he congeal point of the glyceride. This would hinder absorption of aromatics by the glyceride. During pressure release, the condenser liquefies and refluxes a portion of the aroma-containing gases (mostly CO2) escaping from the pressure vessel and returns the condensate to the vessel through the packed column.
The glyceride resulting from the above described process is found to contain more than twice the amount of aromatics obtained from manual mixing of the two components at atmospheric pressure. The aromatized glyceride should then be processed to remove excess water such as by centrifugation.
The aromatized glyceride may be combined with coffee solids either in the fo~m of dry soluble coffeeJ such as by conventional spray plating or any of the techniques disclosed in United States Patent No. 3,769,032 or with a liquid coffee or coffee-like extract, prior to drying the extract. The aromatized glyceride may be solidified, such as by freezing, and comminuted, such as by grinding, prior to being mixed with the soluble coffee powderJ or prior to being combined with a liquid coffee extract, a slushed coffee extract, or a partially frozen slab of coffee extractJ such as disclosed in - commonly-assigned United Stated Patent No. 3J809J766.
The invention will be better understood from the accompanying illustration which shows in cross-section a pressure vessel equipped with means for high pressure reflux and also depicting the multiple phases which can exist within the vessel.

10~'~706 The most readily available source of grinder gas may be obtained by enclosing or hooding coffee grinding equipment, such as the commercial grinders. The gases liberated from the ground coffee may be removed by a pump or rotary blower;
additionally, when desired, a stream of inert, preferably moisture free, gas may be used to sweep gas from the coffee and to have the grinding operation take place in a substantially inert atmosphere. Such a process is described in United States Patent No. 2,156,212 which describes a method of collecting gases evolved during roasting, but which can be equally applied to the collection of gases evolved during the grinding or cellular disruption of whole freshly roasted coffee beans. If pumping is employed, it may be desirable to cool the gas ahead of the pump so that the heat added by pumping will not deteriorate the aromatics contained in the gas.
The chemical composition of the evolved gas is largeiy carbon dioxide together with water vapor and the characteristic aromatic constituents of roasted coffee. The amount of moisture in the gas may be lowered by the use of dry roasting conditions and low-moisture quenches or quenching mediums. The evolved gas is preferably passed through a first condenser where it is cooled to between 35 and 50F and where substantial quantities of water are removed. The relatively low-moisture gas is then fed to a condenser, such as a jacketed, vertically-mounted, scraped-wall heat exchanger, which is cooled by means of a liquid gas refrigerant.
Preferably the condenser is cooled by means of liquid nitrogen and the gas flow into the exchanger is maintained 1a)4~7~
within the range of about 1 to 5 cubic feet per minute per sguare foot of heat exchange surface. The nitrogen gas that evolves from the cooling system is useful as an inert gas stream which might be used elsewhere in the soluble coffee process, such as sweeping grinder gas from the grinder or inert gas packaging of the soluble coffee product.
Ihe aroma bearing gas is condensed into the form of a frost as it comes into contact with the heat transfer wall of the condenser. The frost is removed from the condenser wall and collected for combination with a glyceride carrier. The frost may be held for a short period at low, such as liquid nitrogen, temperatures without deteriorating; however, it is preferred to immediately combine the frost with a glyceride carrier in accordance with this invention. The glyceride, which preferably is coffee oil or a bland-tasting vegetable oil, such as cottonseed, corn or coconut oil, is combined with the frost at a level of about O.S to 6 grams of frost per gram of glyceride, preferably at about 1 to 4 gms. of frost per gm.
of glyceride.
According to this invention, contact between the grinder gas frost and the liquid glyceride phase occurs in a pressure vessel which is equipped for high pressure reflux. A
sufficient amount of the grinder gas frost is added to avoid the pres~nce of an unsaturated CO2 vapor phase. Heat is added to the contents of the vessel, such as by means of a 70F to 85F water jacket, to sublime the grinder gas frost and form a headspace pressure. Rapid heating of the vessel contents to above the congeal point of the glyceride may be desirable in ~ 70 ~
order to increase the period of time during which a liquid glyceride phase is present. At approximately 75 p.s.i.a. solid C2 changes phase to liquid. The temperature corresponding to this phase change is -70F. At this condition, water and any glyceride present, as well as some of the organic aromatics, are in the solid state. The temperatllre of the vessel contents is raised to a point above the congeal point of the glyceride, and preferably to about room temperature, at which condition the grinder gas aromatics will diffuse and establish an equilibrium among the gaseous C02, liquid C02, glyceride and water phases which may be present within the pressure vessel.
Temperatures in excess of about 85F should be avoided as degradation of the coffee aromatics may result. After the frost and glyceride within the vessel have reached the desired temperature, and possibly after an equilibration period of up to several hours, pressure is slowly released, with the use of high pressure reflux.
Slow release of the pressure from within the vessel is desirable in order to maintain the glyceride in a liquid state. Frozen glyceride, which would result from rapid drops in pressure, would not as readily accept transfer of aromatics from the liquid C02 phase with which it is in contact.
According to this invention isothermal venting is thought to be most preferred.
Referring to the drawing, the figure depicts apparatus suitable for batch operation of this invention, the figure showing the state that would exist at equilbrium with the contents of the pressure vessel 1 at about 70F and a 1~4'~70~
pressure of about 855 p.s.i.a. The pressure vessel 1 is surrounded by a water jacket 2 and the vessel is provided with an outlet which directly communicates with ~ packed Column 3.
The partial condenser 4 is preferably adapted for counter-current flow of a liquid heat transfer medium such as 30 to 40F brine or water. A pressure regulator 5 controls the exit of gas from the system and may consist of a single on-off valve and a capillary or small diameter tube which will provide a sufficient pressure drop to prevent a rapid drop of pressure within the vessel.
The vessel contents are shown in four distinct phases including a bottom water phase 6, a liquid glyceride phase 7, a liquid CO2 phase 8, and a saturated gaseous CO2 phase 9.
After the pressure within the vessel is reduced, the aromatized glyceride phase is removed from the vessel. If liquid, this can be done by simply decanting or by draining the liquid through a valve (not shown) in the bottom of the vessel.
It would also be possible to permit residual pressure within the vessel to force the liquid out of a vertical withdrawal tube (not shown) which protrudes through the upper portion of the vessel. The glyceride is then preferably processed so as to remove excess water. If the glyceride is removed from a pressurized vessel, any residual gas present in the vessel may be retained for use in a subsequent pressure fixation cycle.
The aromatized glyceride phase and any water phase which may be present in the vessel may be separated during removal from the vessel. Alternatively, since water will be the heaviest material within the vessel, it would be possible 104'~ 'Cs~
to remove the bottom liquid water phase at any point in the pressure fixation cycle.
Removing water from the aromatized glyceride, prefer-ably down to a level of 0.5% by weight or less, appears to further stabilæe the grinder gas aromatics. Centrifugation, ultracentrifugation, molecular fractionation, drying agents, and like method have proven to be successful techniques for removing water from the aromatized glyceride. As a further refinement of this water removal process, it is possible to separate any aromas from the removed water such as by vacuum distillation and to add these separated aromatics back to the aromatized glyceride.
The aromatized glyceride may be combined with soluble coffee powder or with coffee extract prior to drying the extract in accordance with any of the known prior art techniques. Typical levels of addition for the aromatized glyceride are 0.1 to 2% by weight glyceride based on the weight of soluble solids in the final product. The aromatized powder of this invention may constitute all or only a portion of the powder in the final product, as will be apparent to those skilled in the art.
The terms "coffee powder" and "coffee extract" used in the description of this invention is meant to include material containing in whole or in part coffee substitutes such as powders or extracts obtained in whole or in part from roasted cereals such as wheat, rye, barley and the like. One such item is the water extract and resulting dried powder of wheat, barley and molasses known as "Instan~ Postum."
(Registered trademark) 1~4'Z7Vtj This invention is further described but not limited by the following Example:
Example Coffee grinder gas which was evolved during grinding of freshly roasted coffee beans was passed through a water cooled condenser where 1.25 pounds of water per cubic foot of gas was removed. The gas was then passed to a liquid nitrogen-cooled, scraped-wall heat exchanger where it was condensed and collected as a frost.
80 lbs. of the frost are placed in a 4 cubic foot pressure vessel (as shown in the drawing) together with 40 lbs.
of expressed coffee oil. The pressure vessel is immersed in a water bath maintained at about 70F. After 3 hours, the con-tents of the vessel attain a temperature of about 70F and a pressure of about 850 p.s.i.g. Water at 35F is then counter-currently circulated through the condenser and the pressure regulator valve is then opened slightly to slowly release pressure over the course of 3 hours, care being taken to pre-vent such rapid drops in pressure as would cause the oil to solidify. During the venting process, reflux of CO2 was observed, the liquid condensate returning to the vessel through the packed column filled with ceramic Rasching rings. The vessel contents are centrifuged and about 2 lbs. of water per gallon of liquid is removed. This aromatized "dry" oil, when frozen at -20F, is found to remain stable for at least 3 days and to possess a pleasant coffee aroma which can be transferred to a soluble coffee product by such means as spray plating.

Claims (9)

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

1. A method for aromatizing soluble coffe with an aroma-tized glyceride comprising the steps of:
a) condensing, as a frost, an aroma-containing gas which is obtained by disrupting the cellular structure of freshly roasted coffee and which has a high carbon dioxide content;
b) placing the aroma-containing frost in a pressure vessel, the amount of frost being sufficient to provide a satu-rated carbon dioxide phase within the vessel, and the pressure vessel being directly connected with an overhead packed column and a condenser located above the column;
c) isolating the vessel from the atmosphere;
d) supplying heat to the contents of the vessel to produce a pressure of about 75 psia and an internal temperature of 70°F to 85°F which is above the congeal point of the glyceride;
e) contacting within said heated vessel the frost aromas and a liquid glyceride phase, said glyceride being present in the vessel at a level of about one gram of glyceride to 0.5 to 6 grams of the frost; thereafter, f) slowly releasing pressure from the vessel so that the glyceride is maintained in a liquid state;
g) refluxing the pressurized gas exiting the vessel by means of the condenser; and then h) combining the aromatized glyceride with coffee solids.

2. The method of claim 1, wherein the aromatized glyceride is added to soluble coffee powder.

3. The method of claim 1, wherein the aroma-bearing gas is condensed in a jacketed, vertically-mounted, scraped-wall heat exchanger.

4. The method of claim 3, wherein heat is supplied to the sealed pressure vessel by means of a water bath at 70°F. to 85°F.

5. The method of claim 1, wherein the internal temperature of the vessel is raised to about room temperature.

6. The method of claim 1, wherein the aroma-bearing gas is passed through a condenser where water is removed, prior to being passed into the scraped-wall heat exchanger.

7. The method of claim 1, wherein the pressure within the vessel is released isothermally.

8. The method of claim 1, wherein the vessel contents are maintained above the congeal point of the glyceride in excess of one hour.

9. The method of claim 1, wherein the frost and the glyceride are placed in the vessel before any heat is supplied to the vessel.