GB2117622A - Process for the preparation of soluble coffee - Google Patents

Abstract

To prevent the loss of desirable flavor and aroma volatiles during processing of an aqueous coffee extract obtained from roasted and ground coffee, the overall process of preparing soluble coffee by spray drying a concentrated aqueous extract is improved by employing cold coffee extract in an absorption column to absorb highly volatile coffee flavor and aroma compounds.

Description

SPECIFICATION Process for the preparation of soluble coffee This invention relates to a processforthe preparation of soluble coffee by spray drying a concentrated aqueous coffee extract obtained from roasted and ground coffee.

Work done by Huste et awl., U.S. Patent No.3,345,182, indicates that volatile retention across spray drying is improved with higher solids concentration of aqueous coffee extract. However, since it is economical to operate the percolators at high drawofffactors giving high yields, a low concentration extract is produced.

Therefore, a more effective method of concentrating extract is desirable. However, capturing and retaining volatile coffee flavor and aroma compounds is also essential.

The present invention may be used in an improved version ofthe process disclosed in Shrimpton, U.S.

Patent No.4,107,339. According to the process as described in the patent, a small percent evaporation is followed by a bulk evaporation to produce a high concentration extract. The condensate from the first evaporation is then added backto the concentrate and subsequently is spray dried.

The process as described in the patent is affected by three factors pertaining to the capture and retention of flavor and aroma. First is the small percentevaporation which favors removal of compounds with a high relative volatility (relative to water). Relative volatility (a) is defined as K,/K2 where K is the ratio of vapor concentration to liquid concentration; subscript 1 refers to theflavorand aroma compound being distilled and subscript 2 refers to water. Compounds with a's, i.e., relative volatilities, less than 40 are not removed well. Secondly, condensation favors compounds with low a's. Compounds with high or'sark lost.Thirdly, any compounds that were not removed by the small percent evaporation, are subsequently removed by the large percent evaporation and are discarded.

If one assumes that all flavor compounds are important, then the process as disclosed in the aforementioned U.S. Patent No.4,107,339 has two areas that need improvement The first area is the small percent evaporation. A larger percentevapora- tion could remove heaviervolatiles (low os's), however the increased water load would dilute the product.

Therefore, a means to separate and concentrate the volatiles before addback such as a distillation column is needed. Secondly, the condensercould beim- proved by providing a means of captu ring the highly volatile compounds that are normally lost.

This invention relates to the use of an absorption column for capturing and retaining volatile coffee flavor and aroma compounds by adsorption of the compounds into cold coffee extract. By "cold" is meant coffee extract at a temperature of about 1 00to 15and having a solids concentration of about 10% to 40%, preferably about 35%. As a processing step, the use of the adsorption column permits transfer of desirable coffee flavor and aroma compounds from a venting gaseous stream to a product liquid stream of coffee extract. These flavor and aroma volatiles can then be retained through further processing to the finished product obtained by spray drying the concentrated extract.The gaseous aroma stream can be from any source of volatile aromas, e.g., the vent from a condenser, percolator vent, grinder, etc. Preferably the volatile aromas are the non-condensed flavor and aroma compounds from the condenser. The adsorption column is designed for operation at or slightly above atmospheric pressure; but ifthe gaseous aromas are produced under a vacuum, a sealed gas compressorsuchas,forexample,adiaphragm pump is used to compress the aroma stream, uncontamin- ated, to atmospheric pressure prior to entering the absorption column.

The invention is based on the finding that highly volatile coffee flavor and aroma compounds have a strong affinity for cold coffee extract.

This invention is designed to prevent the loss of desirable flavor and aroma volatiles during processing. In particular, in processes such as,forexample, in Shrimpton U.S. Patent No.4,107,339, it solves the problem of flavour losses during extract evaporation due to poor condensation of highly volatile flavor and aroma compounds in the aroma condenser. It can also be used to solve the problem of losses due to poor condensation ofvolatilesteam aromas in processes such as steam stripping of roast and ground coffee, and forcollection of grinder gas aromasforjar or brew aroma.

Another advantage of thins invention is that it involves the use of relatively low-cost equipment whereas previous equipment for gaseous aroma collectors were high-cost items such as liquid nitrogen condensers or brine-cooled wiped film vapor-liquid contactorssuch as a Votator.Afurtheradvantage of this invention is its multiplicity of uses in processes where it is desirable to capture non-condensable gaseous flavor and aroma compounds for retention through to the finished product.

A process for the preparation of soluble coffee by spray drying a concentrated aqueous coffee extract obtained from roasted and ground coffee has now been discovered in which the improvements which comprise the following steps result in capturing and retaining volatile coffee flavor and aroma compounds: : (a) evaporating an aqueous coffee extractto produce an aqueousflavorand aroma solution; (b) steam stripping the aqueous coffee flavor and aroma solution in a distillation column art a pressure of from 100 to 500 mm Hg absolute to strip flavor and aroma compounds and to obtain a concentrated flavor and aroma solution; (c) condensing the steam strippings in a condenser; (d) compressing the gaseous non-condensed flavor and aroma compounds from steps (a) and (c); (e) passing the compressed gaseous non-condensed flavor and aroma compounds to an absorption column; (f) taking a portion ofthe concentrated stripped extract of (a); (g) passing the concentrated extract of step (f) to said adsorption column countercurrent so asto absorb the compounds of step (e);; (h) combining the steam strippings of step (c), the remainder of concentrated stripped extract of step (a) and the portion of concentrated extract containing the flavor and aroma compounds of step (g); and (i) spray drying the combined strippings and extracts of step (h).

Preferably,theextractofstep (f) is maintained ata temperature of about 1 00to 1 5"C, a concentration of 10% to 40% solids, typically 35%, and a viscosity of 70 to 150 cps. when passed to the absorption column.

The evaporative concentration of step (a) may be carried out in a single effect evaporator such as a Centritherm or a multiple effect evaporator.

The solids concentration of the combined strippings and extracts of step (h) fed to the spray dryer is about 35% to 60%, preferably 40% to 45%.

This invention thus involves the use of a moderately viscous liquid (70 to 150 cps), typically 35% solids concentration, at a temperature of 1 00to 1 50C as the absorbing medium in a gas absorption column.

Generally, absorption columns are not operated with viscous liquids. Previous attempts to absorb gaseous aromas into a viscous liquid, such as concentrated coffee extract were not too successful due to poor operation and foaming, or were deemed economically not feasible. A unique aspect ofthis invention is the use of both gas and liquid streams as continuous phases in the column, thus preventing foam formation and yet providing enough contact area between gas and liquid so as to effect masstransfer ofthe volatiles from the gas to the liquid.

The overall process allows coffee extract to be concentrated from 10% to 20% initial upwards to 35% to 60% solids with minimal flavor and aroma loss.

The overall process involves an initial evaporation step, carried out in a single effect evaporator, followed by two recovery systems. The condensate stream from the single effect evaporator is sentto a distiila tion column where the volatiles are separated and concentrated. The non-condensible streams are recovered in an absorption column by contacting with aroma lean concentrated extract having a viscosity of 70 to 150 cps. and a temperature of about 10 to 1 50C.

The concentrated volatile streams are combined with the concentrated extract stream before spray drying.

The step of steam stripping the aqueous flavor and aroma solution resulting from the concentration/ condensation of extract may be carried out in a distillation column. Volatiles are removed in the lower section of the distillation column called the stripping or exhausting section.

in this section a large amount ofthe liquid is evaporated, and several stages are provided so that volatiles can be removed. In the upper portion ofthe distillation column, called the enriching or rectifying section, the volatiles are concentrated by refluxing liquid back into the column and providing a sufficient number of stages to achieve a desired concentration.

Approximately 75% of the extract feed to an evaporator may be evaporated. In this step, most, perhaps as high as 90%, ofthe volatiles are removed from the concentrate. The extract leaving the evaporator is at a concentration of approximately 52% solids.

Staging of evaporators may be necessary to achieve this concentration. A more efficient evaporator, such as a multiple effect, can be used to perform the bulk of the evaporation.

The distillation column has been designed to recover compounds with a lower limit of relative volatility of 3to 15. The number of actual trays can be determined using standard design method. An advantage in using distillation, as a separating and concentrating device is its flexibility. By altering design and/or operating parameters, compounds with other relative volatilities can be recovered, thus altering the flavorofthefinal product.

Non-condensable vapors from both the evaporator and the distillation column were analyzed and found to contain a quantity of volatiles to impact flavor.

Recoveries on the absorberwere above 95% for carbon compounds.

Spray drying is performed using high concentration extract (43% solids), high spray nozzle pressure (70.3 kg/cm2, 100 psi) and low temperature drying conditions (205in 105"C out, 400"F in, 220"F out).

The spray dried products produced in accordance with this invention have been described as being simiiarto freeze dried. Flavor comments on the products are: winey, buttery, aromatic, groundsy, smooth and well rounded.

This invention is adapted to efficiently recover non-condensablegaseousflavorand aromacom- pounds venting from condensers on an evaporator and distillation column.

1. Feed extract(15% solids) from the percolator scale tank is evaporated undervacuum (125to 150 mm Hg, absolute) in a single stage evaporatorto 55% concentration.

2. The vapors are condensed in a tower water condenser.

3. The non-condensed gaseous aromas arethen compressed to atmospheric pressure and fed to the bottom of the absorption column.

4. The flavor and aroma condensate from step 2 is concentrated in a distillation column 20 fold under vacuum (360 mm Hg, absolute).

5. Non-condensed gaseous aromas from the vacuum distillation column are compressed to atmospheric pressure and fed to the bottom ofthe absorption column.

6. A portion ofthe concentrated extract (10% by solids' weightfrom step 1) is diluted backto 35% solids concentration and fed into the top of the absorber.

Operation is continuous, counter-current.

5. The aroma-rich absorber product is then combined with the liquid aroma from the distillation column and the remainder ofthe concentrated extract.

6. The combined distillate and extracts are then spray dried.

Gas chromatograph analyses of the gas streams were performed. Taste comparisons of absorber feed and absorber product showed the product to contain significantly higher levels of coffee flavor notes predominantly described aswiney, buttery, aromatic, and rich. Gas chromatograms further showed that essentially all the gaseous aromas were recovered from the gaseous stream fed to the absorber.

A study ofthe following products was then run for product evaluation purposes.

1. Commercial freeze-dried coffee product.

2. Spray-dried coffee product according to process of invention (high Colombian blend) 3. Spray-dried coffee product according to process of invention (moderate Colombian blend) 4. Commercial freeze-dried coffee product Atotal of 576 judgements were conducted among respondents who used either non-decaffeinated freeze dried coffee or ground and freeze dried coffee.

Nodifferenceswerefound between thetwo user groups (freeze dried and ground and freeze dried, Dual Users). Results from this test indicated equal preference between products made according to the process of this invention and the commercial freeze-dried coffee products.

Claims (7)

1. A processforthe preparation of soluble coffee by spray drying a concentrated aqueous coffee extract obtained from roasted and ground coffee, in which (a) an aqueous coffee extract is evaporated to produce an aqueous flavor and aroma solution; (b) the aqueous coffee flavor and aroma solution is steam stripped in a distillation column at a pressure of from 100 to 500 mm Hg absolute to stripflavorand aroma compounds and to obtain a concentrated flavor and aroma solution; (c) the steam strippings are condensed in a condenser; (d) the gaseous non-condensed flavor and aroma compounds from steps (a) and (c) are compressed; (e) the compressed gaseous non-condensed flavor and aroma compounds are passed to an absorption column; (f) a portion ofthe concentrated stripped extract of step (a) is taken;; (g) the concentrated extract of step (f) is passed to said adsorption column countercurrent so as to absorb the compoundsofstep (e); (h) the steam strippings of step (c), the remainder of concentrated stripped extract of step (a) and the portion of concentrated extract containing the flavor and aroma compounds of step (g) are combined; and (i) the combined strippings and extracts of step (h) are spray dried.

2. A process as in claim 1 inwhichtheextractof step (f) is maintained at a temperature of 1 00to 15"C and a viscosity of 70to 150 cps. when passed to the absorption column.

3. A process as in either of claims 1 and 2 in which the evaporative concentration step (a) is carried out in a single-effect evaporator.

4. A process as in either of claims 1 and 2 in which the evaporative concentration step (a) is carried out in a multiple effect evaporator.

5. A process as in any one of claims 1 to 4 in which the solids concentration ofthe combined strippings and extracts of step (h) is 40 to 45%.

6. A process forthe preparation of soluble coffee substantially as hereinbefore described.

7. Soluble coffee when produced by a process according to any one of claims 1 to 6.