DK202370242A1

DK202370242A1 - Method for recovery of coffee aroma from a gas stream

Info

Publication number: DK202370242A1
Application number: DKPA202370242A
Authority: DK
Inventors: Kryger Sørensen Jakob
Original assignee: Gea Process Eng A/S
Priority date: 2023-05-22
Filing date: 2023-05-22
Publication date: 2023-06-23

Abstract

In the method for recovering volatile coffee aroma compounds from a gas stream, the method comprises the steps of - providing a gas stream comprising volatile coffee aroma compounds; - providing a scrubbing column operating with a scrubbing liquid; - contacting said gas stream with said scrubbing liquid, thereby allowing the scrubbing liquid to absorb at least a part of said coffee aromas; - recovering scrubbing liquid with absorbed coffee aroma compounds.

Description

DK 2023 70242 A1 1

Title of Invention

Method for recovery of coffee aroma from a gas stream.

Technical Field

The present invention relates to the recovery of coffee aroma com- pounds from a gas stream.

Background Art

Soluble coffee products are used to prepare coffee beverages and are enjoyed all over the world. Soluble coffee is also known as instant coffee.

The production of soluble coffee products starts with green coffee beans which are roasted to provide both flavour and aroma. Subsequently the roast- ed coffee beans are milled and extracted with water to produce coffee extract.

The coffee extract is then processed into soluble coffee products typically by freeze drying or spray drying, typically following a concentration of the coffee extract by evaporation. The coffee flavour and aroma are important parts of the final soluble coffee product and a lack thereof adversely affects the com- mercial viability of the product. Coffee aroma is a complex collection of sever- al organic compounds which provide the aroma of coffee. However, a number of these compounds are both volatile and fragile, i.e. may be decomposed or otherwise lost when exposed to high temperatures. Therefore, a number of steps in the production process can lead to loss of aroma compounds, such as evaporation steps where elevated temperatures and/or vacuum conditions are typically used. Hence, it is common to recover aroma during production to subsequently reincorporate the recovered aroma into the product at latter production steps or into the final soluble coffee product. A number of strate- gies for recovering coffee aroma or maintaining aroma during production ex- ist, such as producing coffee extracts with a high solid content by e.g. coun- ter-current extraction techniques, reducing the need for concentration by evaporation; cut-back techniques, where a small amount of high concentra- tion aroma extract is added to the extract after concentration by evaporation; steam stripping of coffee aroma from the coffee beans and adding the con-

DK 2023 70242 A1 2 densate thereof to the soluble coffee product; and recovering aroma by strip- ping it from liquid coffee extract before evaporation and adding it to the evap- orator concentrate or final soluble coffee product.

In a known method, designed by the applicant, a coffee extract is heated to a temperature of about 100 to 140 °C and then flashed at ambient pressure, generating a vapor fraction and a stripped liquid fraction. In the flash step, the volatile aroma compounds evaporate into the vapor phase whereby the content of volatile aroma compounds in the stripped liquid frac- tion is less than in the influent coffee extract. Subsequently the vapor fraction is condensed and distilled to refine and further concentrate the volatile aroma compounds, which are withdrawn in the distillate. While this has proven to work well, the amount of vapor generated is determined by the temperature of the coffee extract, and as high temperatures adversely affect the aroma com- pounds, the vapor generation and aroma compounds are limited by the tem- perature of the coffee extract.

Hence, there is still a desire to provide further or improved methods for recovery of coffee aroma which are simple, inexpensive and improves or increases the amount of aroma compounds recovered from the coffee extract.

It is therefore an object of the invention to provide further and im- proved methods for recovering aroma compounds from coffee extracts which improves on any of the above problems.

Summary of the invention

These and further objects are met by a method for recovering volatile coffee aroma compounds from a gas stream, said method comprising the steps of - providing a gas stream comprising volatile coffee aroma com- pounds; - providing a scrubbing column operating with a scrubbing liquid; - contacting said gas stream with said scrubbing liquid, thereby allow- ing the scrubbing liquid to absorb at least a part of said coffee aromas; - recovering scrubbing liquid with absorbed coffee aroma com-

DK 2023 70242 A1 3 pounds.

The scrubbing liquid is suitably introduced into the scrubbing column at a temperature in the range of 2 °C to 60 °C, preferably 5 °C to 10 °C, most preferred 6 to 7 °C. The method according to claim 1 or 2, wherein the scrubbing liquid is recirculated from the bottom of the scrubber to the top of the scrubber.

In a particular embodiment the scrubbing liquid is cooled during recirculation.

Suitably the scrubbing liquid, apart from any aroma compounds absorbed from the gas stream during scrubbing, substantially consists of water only.

In a variation of the method the scrubbing liquid is subjected to pH adjustment and/or is provided with one or more antifoam agents, such as

KOH, and/or is provided with an emulsion of droplets of coffee oil, preferably ofan average diameter of 1-5 um.

In yet further embodiments the scrubbing liquid or part of the liquid is taken from an upstream process.

Suitably the scrubbing column comprises a packed bed of a porous material, preferably stainless steel. The scrubbing liquid is supplied to the packed bed at a flow rate of 1000 to 5000 L/h per m? of packed bed that is wetted during scrubbing. Suitably an initial total quantity of scrubbing liquid, prior to the contacting of the gas stream with the scrubbing liquid, amounts to 50 to 500 L per m? of packed bed that is wetted during scrubbing.

The gas stream is suitably contacted with the scrubbing liquid at substantially ambient pressure.

The gas stream is contacted with the scrubbing liquid at a pressure of 200 to 2000 mbara.

In a further variation the coffee aroma depleted gas stream is recirculated from the top of the scrubber to the bottom of the scrubber.

Preferably the gas stream originates from a process of aroma recovery from a coffee extract, from coffee roasting, or from coffee

DK 2023 70242 A1 4 prewetting. And even more preferred the scrubbing liquid also originates from such a process.

Suitably the recovered scrubbing liquid with absorbed aroma compounds is further processed by concentration, drying, freezing or freeze- drying, optionally for use in a soluble coffee product.

Alternatively the recovered scrubbing liquid with absorbed aroma compounds is applied directly to a soluble coffee product.

Suitably the coffee aroma depleted gas stream leaving the scrubber is subjected to one or more steps of condensation.

Brief Description of Drawings

In the following the invention will be described with reference to the exemplary embodiments shown in the figures, wherein

Fig. 1 shows a generic process for recovering aroma compounds ac- cording to the invention;

Fig. 2 shows another embodiment of the process for recovering aro- ma compounds, where the aroma rich gas is scrubbed according to the inven- tion.

Detailed Description

Fig. 1 shows a process scheme including the method of the inven- tion, wherein the aroma compounds are recovered from a coffee extract 1.

Not all the equipment and instrumentation which may be part of the process is shown. The coffee extract 1 is provided to a two-fluid nozzle 100 by way of pump 20. A heat exchanger 21 is provided to pre-heat the coffee extract 1, this pre-heating is optional but shown for illustration. The coffee extract 1 is supplied to a first channel 101 of the two-fluid nozzle and a steam flow 2 is provided to a second channel 102 of the two-fluid nozzle. The two-fluid nozzle 100 is here shown in a schematic manner and is in this embodiment an inter- nally mixing two-fluid nozzle, hence a mixing zone 103 is provided within the two-fluid nozzle. The coffee-extract 1 and steam flow 2 are contacted in the mixing zone 103 whereby the coffee extract is atomized to provide a spray 3

DK 2023 70242 A1 of coffee extract droplets in steam. The two-fluid nozzle 100 sprays directly into a gas-liquid separator 200, which is here shown as a flash chamber. Up- on atomization, aroma compounds are stripped from the coffee extract drop- lets into the gas phase, which forms the feed for the method of the invention. 5 In the gas-liquid separator 200, the flow velocity is such that the liquid drop- lets of the spray 3 are allowed to settle and a stripped coffee extract 4 is re- covered, i.e. withdrawn, from the bottom of the gas-liquid separator 200, e.g. by way of a pump (not shown). The gas phase of the gas-liquid separator 200 is recovered, i.e. withdrawn, as an aroma rich gas 5. In the conventional manner a demister (not shown) may be provided in or in conjunction with the gas-liquid separator 200 to catch small droplets entrained in the gas phase.

The stripped coffee extract 4 has a lower content of aroma compounds than the coffee extract 1. The aroma rich gas 5 is further processed according to the invention. The above is one way of providing the coffee aroma rich gas it is however contemplated that a coffee aroma rich gas may be supplied in any other way and the invention should not be limited to the above embodiment included for illustrative purpose only.

Fig. 2 shows an embodiment of the invention. The feed may follow from the method shown in figure 1 in which the feed for the coffee aroma con- taining gas is generated, but the feed 5 can be any coffee aroma rich gas.

The aroma in the aroma rich gas 5 is processed according to the invention by capturing the coffee aroma in a scrubbing liquid in scrubbing column 400. The aroma rich gas 5 is fed to scrubbing column 400 at a position in the lower part of the column 402. A bottom fraction 9 is withdrawn from the scrubbing col- umn consisting of scrubbing liquid, water, or substantially of water, and the captured coffee aroma. The off gas 10 contains the coffee aroma depleted gas.

The scrubbing liquid, 6, is fed to the top portion, 401, of the scrubbing column preferably through a cooler 403 to provide a cool scrubbing liquid (through a cooler is shown as a dashed line in figure 2). The scrubbing liquid, optionally or preferably cooled, drizzles down through the packed bed in countercurrent flow with the aroma rich gas whereby a substantial part of the

DK 2023 70242 A1 6 coffee aroma is captured by the cool water.

The coffee aroma enriched scrubbing liquid is then treated by any of the methods (for example condensation, evaporation freeze concentration, or distillation) that may be suitable to recover the aroma and pure water. The water may be reused as the scrubbing liquid. It is also contemplated that the aroma depleted off gas, 10, is recirculated to the bottom of the scrubbing col- umn and is reintroduced in order to recover further coffee aroma.

Claims

DK 2023 70242 A1 7 Claims

1. A method for recovering volatile coffee aroma compounds from a gas stream, said method comprising the steps of - providing a gas stream comprising volatile coffee aroma com- pounds; - providing a scrubbing column operating with a scrubbing liquid; - contacting said gas stream with said scrubbing liquid, thereby allow- ing the scrubbing liquid to absorb at least a part of said coffee aromas; - recovering scrubbing liquid with absorbed coffee aroma com- pounds.

2. The method according to claim 1, wherein the scrubbing liquid is introduced into the scrubber at a temperature in the range of 2 °C to 60 °C, preferably 5 °C to 10 °C, most preferred 6 to 7 °C.

3. The method according to claim 1 or 2, wherein the scrubbing liquid is recirculated from the bottom of the scrubber to the top of the scrubber.

4. The method according to claim 3, wherein the scrubbing liquid is cooled during recirculation.

5. The method according to any of the previous claims, wherein the scrubbing liquid, apart from any aroma compounds absorbed from the gas stream during scrubbing, substantially consists of water only.

6. The method according to any one of claims 1 to 4, wherein the scrubbing liquid is subjected to pH adjustment and/or is provided with one or more antifoam agents, such as KOH, and/or is provided with an emulsion of droplets of coffee oil, preferably of an average diameter of 1 to 5 um.

7. The method according to any one of claims 1 to 4, wherein the scrubber liquid is a coffee extract.

8. The method according to any one of the previous claims, wherein the scrubbing column comprises a packed bed of a porous material, prefera- bly stainless steel.

9. The method according to any one of claims 6 to 7, wherein the scrubbing liquid is supplied to the packed bed at a flow rate of 1000 to 5000 L/h per m? of packed bed that is wetted during scrubbing.

DK 2023 70242 A1 8

10. The method according to any one of claims 3 to 8, wherein an ini- tial total quantity of scrubbing liquid, prior to the contacting of the gas stream with the scrubbing liquid, amounts to 50 to 500 L per m? of packed bed that is wetted during scrubbing.

11. The method according to any one of the previous claims, wherein the gas stream is contacted with the scrubbing liquid at substantially ambient pressure.

12. The method according to any one of claims 1 to 11, wherein the gas stream is contacted with the scrubbing liquid at a pressure of 200 to 2000 mbara.

13. The method according to any one of the previous claims, wherein the gas stream is recirculated from the top of the scrubber to the bottom of the scrubber.

14. The method according to any one of the previous claims, wherein the gas stream originates from a process of aroma recovery from a coffee extract, from coffee roasting, or from coffee prewetting.

15. The method according to any one of the previous claims, wherein the recovered scrubbing liquid with absorbed aroma compounds is further processed by concentration, drying, freezing or freeze-drying, optionally for use in a soluble coffee product.

16. The method according to any one of claims 1 to13, wherein the recovered scrubbing liquid with absorbed aroma compounds is applied direct- ly to a soluble coffee product.

17. The method according to any one of the previous claims, wherein a gas stream leaving the scrubber is subjected to one or more steps of con- densation.