APPARATUS AND METHODS FOR PROCESSING COFFEE GROUNDS

Abstract

A method of processing coffee grounds. The method includes drying coffee grounds to at least a predetermined dryness by using a rotatory drier to heat and agitate the grounds while measuring the dryness of the drying coffee. After the coffee grounds have been dried, they are mixed with supercritical CO.sub.2 to separate liquid components of the coffee grounds from solid components. This provides a simple, safe way of extracting coffee oil and producing coffee flour.

Claims

1. A method of processing coffee grounds, comprising: drying coffee grounds to at least a predetermined dryness by using a rotatory drier to heat and agitate the coffee grounds while measuring the dryness of the drying coffee grounds; and mixing the dried coffee grounds with supercritical CO.sub.2 to extract liquid components of the coffee grounds from solid components.

2. The method according to claim 1, wherein the dried coffee grounds contain 5% water or less by weight.

3. The method according to claim 1, wherein the dried coffee grounds contain between 2-5% water by weight.

4. The method according to claim 1, wherein the coffee grounds are dried at a temperature of between 145° F. and 175° F.

5. The method according to claim 1, wherein the rotary drier comprises a rotating drum to contain the coffee grounds.

6. The method according to claim 1, wherein the rotary drier comprises rotating agitators which rotate within a drum configured to contain the coffee grounds.

7. The method according to claim 1, wherein the rotary drier comprises rotating auger which rotate within a drum to agitate and more the drying coffee grounds.

8. The method according to claim 1, wherein the dryness is measured by a humidity sensor mounted in an extraction outlet of the drier.

9. The method according to claim 1, wherein the method comprises sifting the remaining solid coffee grounds to produce coffee grounds flour.

10. The method according to claim 1, wherein the fluid comprises oil, waxes and saponification fluids.

11. The method according to claim 1, wherein the temperature of the supercritical CO.sub.2 is between 31° C. and 160° C.

12. The method according to claim 1, wherein the pressure of the supercritical CO.sub.2 is between 280 and 320 atm.

13. The method according to claim 1, wherein the dryness is measured by measuring the water activity of the grounds.

14. The method according to claim 1, wherein the pressure and temperature of the supercritical CO.sub.2 is adjusted during extraction to extract different fractions of the liquid components at different times.

15. The method according to claim 1, dried coffee grounds are mixed with supercritical CO.sub.2 for between 1-10 hours.

16. The method according to claim 1, wherein the method is performed in batches of between 1-10 kg.

17. The method according to claim 1, wherein the method is performed in batches of between 10-150 kg.

18. The method according to claim 1, wherein the method comprises soaking the dried coffee grounds in liquid CO.sub.2.

19. The method according to claim 1, wherein the method comprises soaking the dried coffee grounds in liquid CO.sub.2 for at least 30 minutes prior to extraction.

20. An apparatus for processing coffee grounds, comprising: a rotary drier configured to receive coffee grounds, the rotatory drier comprising: a heater configured to heat the received coffee grounds; a rotary agitator configured to agitate the received coffee grounds; and a sensor configured to measure the dryness of the received coffee grounds during drying; wherein the rotary drier is configured to dry the received coffee grounds to at least a predetermined dryness; and a supercritical CO.sub.2 extraction assembly comprising: an extraction vessel configured to receive the dried coffee grounds from the rotary drier; a source of CO.sub.2; a heater and a pump configured to condition the CO.sub.2 received from the CO.sub.2 source to be in a supercritical state within the vessel; and an outlet for extracting liquid components of the coffee grounds from the n extraction vessel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Various objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the invention. Similar reference numerals indicate similar components.

[0054] FIG. 1 is a schematic diagram of the apparatus used to carry out the extraction of oil from coffee grounds.

[0055] FIG. 2 is a flow chart showing how coffee grounds are processed to extract liquid components and to produce coffee flour.

DETAILED DESCRIPTION

Introduction

[0056] Brewed coffee is made mixing water with ground coffee beans (typically at high temperature and pressure), then allowing to brew. There are several methods for doing this, including using a filter, a percolator, and a French press. Terms used for the resulting coffee often reflect the method used, such as drip brewed coffee, filtered coffee, pour-over coffee, immersion brewed coffee etc. Water seeps through the ground coffee, absorbing its constituent chemical compounds, and then passes through a filter. The used coffee grounds are retained in the filter, while the brewed coffee is collected in a vessel such as a carafe or pot.

[0057] The coffee grounds are typically then discarded, or used directly, for example, as garden mulch. However, the coffee grounds typically retain valuable products which may be extracted and used. These include the liquid components of the grounds which were not extracted by the brewing process (e.g. oil, waxes and saponification fluids) and the remaining solid materials.

[0058] Spent coffee grounds contain approximately 10-15% by weight of oil. The main fatty acid constituents are palmitic, linoleic, oleic, stearic and arachidic1. Spent coffee grounds also contain phenolic compounds including chlorogenic acid, caffeoylquinic acid, dicaffeylquinic acid, feruloylquininc acid and p-coumarolyquinic acid.

[0059] Typically, the extraction process used to extract liquid components from coffee grounds involve the use of hexane (a non-polar liquid hydrocarbon solvent).

[0060] The inventors have realized that by combining drying a rotary drier with super-critical CO.sub.2 extraction, improved extraction results may be obtained. Advantages of the present invention may include: [0061] the products have fewer pathogens: the rotary drier ensures that the grounds are dried evenly to kill off pathogens. Remaining pathogens would be killed by the super-critical CO.sub.2. [0062] The products have fewer dangerous chemicals present: Because CO.sub.2 is a gas at room temperature it automatically is evaporated from the products (unlike, for example, hexane or toluene). [0063] The extraction fluid can be easily recycled: Again, because CO.sub.2 is a gas at room temperature it can easily be removed, captured and recycled for further extractions. [0064] The CO.sub.2 extraction stage is more effective when the grounds are dried in a rotary drier: By agitating and mixing the grounds as they dry, clumps or crusts of coffee grounds do not form (e.g. as may be the case using oven drying in trays). This helps ensure that the humidity measurements are more accurate, and that the super-critical CO.sub.2 is able to access the liquids within the grounds more easily. [0065] The remaining solids are produced in a useful flour form: the super-critical CO.sub.2 extraction step aids in forming the coffee grounds to form into a flour, which can then be used directly after sifting without further milling. [0066] Utilizing our technology, we eliminate a specific waste stream from the coffee industry, spent coffee grounds.

[0067] Various aspects of the invention will now be described with reference to the figures. For the purposes of illustration, components depicted in the figures are not necessarily drawn to scale. Instead, emphasis is placed on highlighting the various contributions of the components to the functionality of various aspects of the invention. A number of possible alternative features are introduced during the course of this description. It is to be understood that, according to the knowledge and judgment of persons skilled in the art, such alternative features may be substituted in various combinations to arrive at different embodiments of the present invention.

Apparatus

[0068] FIG. 1 shows a schematic of an apparatus 100 for extracting liquid components from coffee grounds. The apparatus is configured to take used coffee grounds and first dry them using a rotary drier, and then extract liquid components using super-critical CO.sub.2. In some embodiments, the dried grounds are milled or further ground before the extraction phase

Drying

[0069] As shown in FIG. 1, the dryer 101 comprises a drum 106 and a rotating agitator 102. The rotating agitator rotates within the drum to mix the coffee grounds to prevent them forming clumps or a crust, and to ensure that they are evenly dried. The rotating agitator sweeps out substantially the entire volume of the cylindrical drum to ensure that all the grounds contained in the drum are moved during a rotation cycle. Evenly drying the coffee grounds also ensures that the humidity measurements are more accurate. That is, they are representative of all the grounds within the dryer, rather than just the portions closest to the humidity meter. In this case the rotation axis of the rotary drier is aligned with the horizontal.

[0070] In this case, the drier utilizes heat and agitation to keep the grounds moving. This movement also creates airflow. Airflow in this case, is also provided by cycling air into the drier through air inlet 103a and out of the drier (along with evaporated water) through air outlet 103b. This ensures proper drying as well as eliminating pathogens. Using heat and agitation allows the grounds to be dried and pasteurized in one step. The drier is configured to ensure a moisture content below 11% which helps ensure that there are no pathogens in the dried grounds. In this case, the humidity of the grounds can be measured by measuring the humidity of the air passing through the air outlet 103b using a humidity sensor 104. In other embodiments, the dryness of the grounds is measured in terms of the water activity, and the drier is configured to ensure a water activity of less than a predetermined threshold (e.g. 0.3).

[0071] Commercial dehydrators are unable to dehydrate and pasteurize in one step, requiring a second step and an increase in power usage and cost. Dehydrating alone can leave bacterial compounds behind, leading to salmonella poisoning. The temperatures used in the present technology enable pasteurization.

[0072] Agitating the grounds as they dry ensure that the grounds dry evenly and do not form clumps or aggregates of coffee grounds stuck together. It is important that the granular structure of the grounds is maintained so that, in the extraction step, the supercritical CO.sub.2 can access the liquid components of the grounds. Extraction is a diffusion-based process, in which the solvent is required to diffuse into the matrix and the extracted material to diffuse out of the matrix into the solvent. Reducing the distance by maintaining the granular structure of the grounds may significantly speed up the time required to extract the liquid components from the grounds. In contrast, if the grains of coffee grounds form a solid superstructure (e.g. clumps or a crust), the supercritical CO.sub.2 extraction step may be much slower.

[0073] Experiments by the inventors have established that the technology can dry the coffee grounds to a moisture content of less than 11% and be pathogen free.

[0074] Once the coffee grounds are dried and pasteurized, they are placed in an extraction vessel for supercritical CO.sub.2 extraction. In some embodiments, the dried grounds are directly transmitted to the extraction vessel. Limiting exposure to the atmosphere may help prevent the coffee grounds reabsorbing water from the atmosphere and or capturing new pathogens.

Extraction

[0075] Once the spent coffee grounds are dry, supercritical CO.sub.2 extraction is used to remove the oil, waxes and saponification fluids (triglycerides) from the cellular walls of the coffee grounds. This process also helps pulverize the solid components of the coffee grounds into particles that have the consistency of flour. This means that the solids only need to be mechanically sifted to separate a saleable flour product. That is, the remaining solids may be sifted directly after the supercritical CO.sub.2 extraction to form the flour (e.g. without an intermediate grinding step).

[0076] To perform an extraction, the dried coffee grounds are placed into an extraction vessel 114a and/or 114b. In this case, the system has multiple extraction vessels which allow the system to operate continuously, while each vessel operates as a batch process.

[0077] In this case, CO.sub.2 gas is introduced into the extraction vessel 114a, 114b from a CO.sub.2 source vessel 111. In this case, the gas from the source vessel is first cooled using a cooler 112, then pumped into the vessel 114a,b using a pump 113. The temperature within the vessel 114a,b is controlled by placing the vessels within an oven 115 which can be heated and cooled as required. The conditions of temperature and pressure within the extraction vessels are controlled by controlling the pressure of the pump 113 and the temperature of the oven 115. These conditions are controlled to force supercritical CO.sub.2 into the extraction vessel where it interacts with the coffee grounds, where it dissolves part of the coffee grounds. These dissolved components are the extracted liquid components 121. When the pressure is reduced on the extracted liquid components 121, the CO.sub.2 turns to gas and can be recycled.

[0078] By changing the temperature and pressure as well as flow rate, certain molecules will bond to CO.sub.2, allowing them to be separated from the coffee grounds. Circulating CO.sub.2 at pressures of around 4300 psi (e.g. between 3900 psi to 4400 psi, or between 26.5 MPa to 28.5 MPa) and temperatures of around 55° C. (e.g. between 40-65° C.) extracts the oils, waxes, and saponification of fatty acids. For example, the extraction may take place at 4350 psi and 120° F. (50° C.). As the CO.sub.2 travels through the coffee grounds it liberates these components from the cell walls of the spent coffee grounds.

[0079] This process also reduces the grain size of the spent coffee grounds to a consistency common with flour. This reduces the need to mill the flour, reducing both costs and power usage.

[0080] In this embodiment, once the CO.sub.2 is released from the solute, it is recycled back into the tank to be used during the next batch.

[0081] By using supercritical CO.sub.2, the user has control over the procedure, CO.sub.2 can be recycled, making this method more environmentally friendly compared to others. Further, regulatory authorities, such as the U.S. Federal Drug Administration (FDA), consider CO.sub.2 safe for industrial extractions. Although the drying process in this embodiment provides a pathogen-free starting product for the extraction, the CO.sub.2 may also act as a cleaning agent by removing remaining microbial bacteria, molds, and mildews. The yield using supercritical CO.sub.2 is typically higher than other extraction methods; however, the yield and quality of product is sensitive to changes in the physical properties of the starting material. The inventors have found that using a rotary drier to agitate the raw grounds while drying provides a more consistent starting material for the extraction process.

[0082] Extracts obtained from supercritical CO.sub.2 extraction are appealing to the food and beverage and medical industries, because no residual solvent will remain on the product at room temperature and pressure (because CO.sub.2 is a gas under these conditions). Because there is no residual solvent on the product, the extract will be purer than many solvent-based extraction methods. For example, because the most-commonly used solvent, hexane, is a liquid at room temperature, The grounds need to be dried prior to the extraction process and need to be dried again to be utilized for anything else. The system uses a lot of energy and also uses a hydrocarbon to create the oil. The typical drying process is also not enough to kill all pathogens, meaning there is a chance you still have bacteria in the grounds which may lead to salmonella poisoning. In addition, recycling of hexane is limited because typically only 60% of the hexane can be recaptured in a cooling tower.

Sifting

[0083] As noted above, supercritical CO.sub.2 extraction causes the solid components of the grounds to break up into a material with the consistency of flour. This flour can be separated using a simple mechanical sifter to produce a saleable flour product (e.g. using 200 or 212 micron mesh). That is, no further mechanical milling is required. This may significantly reduce operation costs. The flour component may be greater than 70% of total solids by weight.

Method

[0084] FIG. 2 is a flow chart showing how coffee grounds are processed to extract liquid components and to produce coffee flour (e.g. using the apparatus of FIG. 1).

[0085] The method comprises drying 181 coffee grounds to at least a predetermined dryness by using a rotatory drier to heat and agitate the grounds while measuring the dryness of the drying coffee.

[0086] Then, the dried coffee grounds are mixed 182 with supercritical CO.sub.2 to separate liquid components 121 of the coffee grounds from solid components.

[0087] The separated solid coffee grounds are then sifted to produce coffee grounds flour 122 and a coarser-grained solids 123.

End Products

[0088] The end products are safe for consumption. For example, the coffee oil can be used in the pharmaceutical, cosmetic, food industry and textile industry.

[0089] Coffee oil may be used as a high quality and cost-effective feedstock for biodiesel production compared to other waste sources. It is less expensive, has higher stability (due to its high antioxidant content), and has a pleasant smell.

[0090] The sifted coffee flour may be used in baking as a substitute or partial replacement for wheat flour. Coffee flour does not contain gluten, and so can be safely consumed by gluten-intolerant individuals. Coffee flour may also be a source of fiber, minerals (e.g. magnesium) and/or antioxidants.

Experimental Results

[0091] A 3-day trial of 3 extractions at varied pressures and temperatures utilizing a total of 120 L of spent coffee grounds was conducted. Extraction #1 was conducted at 200 bar (197 atm) and 50° C., extraction #2 was performed at 300 bar (296 atm) and 50° C., and extraction #3 was conducted at a pressure of 350 bar (345 atm) and 58° C. All three tests gave different results, extraction #1 provided a slightly higher ratio of extracted material. However, extraction #2 gave a greater portion of the more valuable dark coffee oil fraction. This illustrates that the reaction conditions can be tailored to control the materials extracted.

[0092] A Vitalis™ Q90H was used for all three extractions. One extraction chamber was filled with spent coffee grounds dried to less than 10% moisture content and ground to approximately <1 mm. Both cyclone and separator series were used for collection to maximize flow rate. For each extraction, total percent mass extracted was calculated using the following formula:

Total percent mass extracted=Total mass extracted×100/Total feedstock input mass

[0093] The average extraction results for each run are shown in Table 1. How the extraction proceeds over time is shown in Table 2. These values were obtained using the batch data from the HMI recorded during the runs. Extraction 1 and its associated parameters produced an extraction yield of 15.79% after 7 hours. Extraction 2 yielded significantly more in the first hour than the other two extractions. This may be due in part to the 1-hour soaking time before starting the run. Extraction 3 with the highest pressure and temperature yielded the lowest of the three runs.

[0094] Andrade et al. states that the effect of temperature, at constant pressure, occurs by two mechanisms. Firstly, the increase in temperature increases the solubility due to increased vapor pressure of the solute. Conversely, it reduces the solubility due to the decrease in density of the solvent. These two opposite effects result in the crossover of the isotherms and decrease the strength of the solvent. This helps explain the lower extraction yield shown in Extraction 3. The extract separated into layers with different amounts being extracted at different times depending on the parameters for that extraction run.

[0095] Visual inspection of the extracted material indicates that there are multiple distinct layers. The ratio of the size of the layers is different for different extraction conditions. Analytic results of one of the extractions showing the variety of compounds extracted are shown in Table 3.

TABLE-US-00001 TABLE 1 Extraction Results Extraction 1 Extraction 2 Extraction 3 Average Extraction 2901.14 4302.99 4508.68 Pressure (psi) Average Extraction 118.98 121.25 131.11 Temperature (F) Average Cyclone 55.77 55.13 56.26 Temperature (F) Average Flow Rate (kg/min) 3.01 2.95 2.45 Total CO.sub.2 Mass (kg) 1264.20 1062.00 882.00

TABLE-US-00002 TABLE 2 Cumulative Extracted Mass Extraction 1 Extraction 2 Extraction 3 Feedstock Input Mass 18432.2 g 18141.4 g 17980.4 g 1 hr  469.7 g  966.0 g  609.2 g 2 hr  889.9 g  1454.2 g  1113.2 g 3 hr  1561.1 g  1925.8 g  1597.0 g 4 hr  2082.3 g  2329.4 g  1931.4 g 5 hr  2477.3 g  2621.0 g  2131.8 g 6 hr  2743.7 g  2751.4 g  2385.8 g 7 hr  2910.5 g — — Total Percent Mass   15.79%   15.17%   13.27% Extracted

TABLE-US-00003 TABLE 3 Analytical Testing Results for 300 bar and 50° C. Component Heavy Medium Light C10:0 Capric 0.3 <0.03 n/a C12:0 Lauric 0.41 <0.03 <0.03 C14:0 Myristic 0.27 0.09 0.1 C15:0 Pentadecanoic n/a 0.03 0.04 C16:0 Palmitic 32.5 36.1 37.2 C16:1Tn7 Trans n/a 0.33 3.15 Palmitelaidic C16:1n7 Palmitoleic 0.18 0.03 0.04 C17:0 Heptadecanoic n/a 0.33 0.14 (Margaric) C18:0 Stearic 8.7 7.97 7.19 C18:1n9 Oleic 7.52 7.38 6.84 C18:1Tn9 Trans n/a 0.07 0.63 Elaidate C18:1n7 Vaccenate 0.43 0.5 0.51 C18:2n6 Linoleic 40 39.2 35.3 C18:2Tn6 Trans n/a 0.06 0.56 Linoelaidate C18:3n3 Aplha- 1.45 1.35 1.22 Linolenic C18:4n3 n/a 0.09 0.07 Octadecateraenoic C19:0 Nonadecanoic n/a 0.09 0.07 C19:1Tn12 Trans 0.16 0.22 2.05 Nonadecanoate 7 C20:0 Arachidic 3.8 3.5 2.88 C20:1n9 Eicosenoic 0.34 0.38 0.4 11 C20:1Tn9 Trans n/a 0.05 0.25 Eicosenoate 11′ C20:2n6 <0.03 0.07 0.06 Eicosadienoic 11, 14 C20:5n3 n/a n/a <0.03 Eicosapentaenoic C22:0 Behenic 2.16 1.48 0.74 C22:1n9 Erucic n/a <0.03 0.06 C22:2n6 n/a n/a <0.03 Docasadienoic C22:4n6 n/a n/a <0.03 Docosatetraenoic C22:5n3 n/a n/a 0.04 Docosapentaenoic C22:6n3 n/a 0.06 0.03 Docosahexaenoic C24:0 Lignoceric 0.73 0.47 0.27 Others 1.09 0.25 0.13 Saturates 48.8 50 48.8 Monounsaturates 8.47 8.3 7.85 Polyunsaturates 41.4 40.9 36.7 Trans 0.16 0.72 6.64 Omega 3 1.45 1.51 1.36 Omega 6 40 39.4 35.4 Omega 9 7.86 7.78 7.31

[0096] The most abundant acids are Palmitic acid, Stearic acid, Oleic acid and Linoleic acid. Palmitic acid trends upward from heavy to light while Stearic acid, Oleic acid and Linoleic acid trend downward from heavy to light. The heavy fraction has the least number of fatty acids at 17 and the light has the greatest number of fatty acids at 30. The medium fraction has 27.

[0097] Although the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof, it is not to be so limited since modifications and changes can be made therein which are within the full, intended scope of the invention as understood by those skilled in the art.

BIBLIOGRAPHY

[0098] 1. Muangrat, Rattana & Pongsirikul, Israpong. (2019). Recovery of spent coffee grounds oil using supercritical CO2: extraction optimization and physicochemical properties of oil. CyTA-Journal of Food. 17. 334-346. 10.1080/19476337.2019.1580771. [0099] 2. Andrade, Kátia & Gonçalvez, Ricardo & Maraschin, Marcelo & Ribeiro-do-Valle, Rosa & Martinez, Julian & Ferreira, Sandra. (2012). Supercritical fluid extraction from spent coffee grounds and coffee husks: Antioxidant activity and effect of operational variables on extract composition. Talanta. 88. 544-52. 10.1016/j.talanta.2011.11.031.