Used coffee grounds

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Used coffee grounds
Ground coffee in boxes.jpg
Used coffee grounds in boxes.
Usage

Used coffee grounds is the result of brewing coffee, and are the final product after preparation of coffee. Despite having several highly-desirable chemical components, used coffee grounds are generally regarded as waste, and they are usually thrown away or composted. As of 2019, it was estimated that over 15 million tonnes of spent coffee grounds are generated annually. Due to this quantity of waste and the chemical properties of used coffee grounds, potential uses for used coffee grounds are a hot topic of investigation as of the 2010s.

In the late 19th century, used coffee grounds were used to adulterate pure coffee.[1]

Chemical composition[edit]

Used coffee grounds are rich in sugars,[2] which comprise about half of their weight. A further 20% is made up of proteins, and a further 20% is lignins.[3] The dry coffee grounds contain significant amounts of potassium (11.7 g/kg), nitrogen (2.8 g/kg), magnesium (1.9 g/kg), and phosphorus (1.8 g/kg).[4] The quantity of caffeine remaining in used coffee grounds is around 48% of that in fresh coffee grounds.[5] There are significantly less tannins in used coffee grounds than fresh coffee grounds.[6]

Production[edit]

On average, 1 tonne of green coffee produces approximately 650 kg of spent coffee grounds,[7] and over 15 million tonnes of spent coffee grounds are generated annually.[8] In keeping with a life cycle approach to sustainability,[9] this large quantity of waste requires waste management plans. Due to the amount of spent coffee grounds generated and the chemical properties of spent coffee grounds, the usage of spent coffee grounds is avidly investigated.[5]

Usage[edit]

In gardens[edit]

Composting worms moving about in used coffee grounds.

In gardens, coffee grounds may be used for composting or as a mulch[10] as they are known to slowly release nitrogen into the soil. They are said to be especially appreciated by worms and acid-loving plants such as blueberries,[11] although due to acids being leached from the grounds while in use, they typically have a neutral pH,[12] and red wiggler growth and survival has been experimentally tested and found to be reduced in treatments using used coffee grounds as the primary feedstock for the worms.[13] Used coffee grounds are particularly noted as a soil amendment.[12] Spent coffee grounds have phytotoxic properties which can be reduced through composting.[14] Gardeners have reported the use of used coffee grounds as a borer,[15] slug and snail repellent,[10][16] but this has not yet been scientifically tested.[17] Some commercial coffee shops run initiatives to prevent the grounds from going to waste, including Starbucks' "Grounds for your Garden" project,[18] and community sponsored initiatives exist, such as "Ground to Ground" [19] or the 'Green Coffee Shop Scheme' in Cambridgeshire, UK.[20]

Coffee grounds ready for divination

Use in fortune telling[edit]

In divination and fortune-telling the patterns of coffee grounds are used for predictions.

Other uses[edit]

Oyster mushroom mycelium on coffee grounds.

Initiatives have succeeded using coffee grounds as a substrate for the cultivation of mushrooms (including oyster mushrooms).[21][22] The use of spent coffee grounds in this application has the advantage of the used coffee grounds needing no pre-treatment to be usable as a mushroom substrate.[5] Used coffee grounds have other homemade uses in wood staining, air fresheners, and body soap scrubs.[10] They may also be used industrially in biogas production or to treat wastewater.[17] Bioethanol may also be produced from the sugar content of spent coffee grounds, after it is defatted as a pre-treatment, it is typically hydrolysed by dilute acid.[3] In 2021, Gloucestershire-based football club Forest Green Rovers trialled a kit made from 35% used coffee grounds combined with recycled plastic.

It is not recommended to burn dried used coffee grounds, as they give off hazardous nitrogen oxides when burnt.[3]

It has been proposed to use spent coffee grounds to feed ruminants, pigs, chickens and rabbits, but the high lignin content makes this an undesirable use.[23]

Dried used coffee grounds were recommended to fill pincushions.[24]

It has been suggested to recover caffeine from used coffee grounds for commercial applications in agrifood, cosmetic, nutraceutic or pharmaceutic industries.[25]

Application of 10 kg used coffee grounds per square metre has been suggested as part of a crop rotation system, where for the first six months, the field is allowed to lie fallow with a layer of coffee grounds on it suppressing weed growth, then the coffee grounds are plowed in and legumes are grown, which fix their own nitrogen. Application of an equal amount of horse manure at the same time as the coffee grounds has been shown to nearly eliminate negative effects of fresh used coffee grounds.[26]

See also[edit]

References[edit]

  1. ^ Pendergrast, Mark "Uncommon grounds : the history of coffee and how it transformed our world" 2010 Basic Books. ISBN 978-0-465-02404-9
  2. ^ Mussatto, Solange I.; Carneiro, Livia M.; Silva, João P.A.; Roberto, Inês C.; Teixeira, José A. (January 2011). "A study on chemical constituents and sugars extraction from spent coffee grounds". Carbohydrate Polymers. 83 (2): 368–374. doi:10.1016/j.carbpol.2010.07.063. hdl:1822/16744.
  3. ^ a b c McNutt, Josiah; He, Quan (Sophia) (March 2019). "Spent coffee grounds: A review on current utilization". Journal of Industrial and Engineering Chemistry. 71: 78–88. doi:10.1016/j.jiec.2018.11.054. S2CID 104298839.
  4. ^ Ballesteros, Lina F.; Teixeira, José A.; Mussatto, Solange I. (December 2014). "Chemical, Functional, and Structural Properties of Spent Coffee Grounds and Coffee Silverskin". Food and Bioprocess Technology. 7 (12): 3493–3503. doi:10.1007/s11947-014-1349-z. hdl:1822/31900. S2CID 38776511.
  5. ^ a b c Campos-Vega, Rocio; Loarca-Piña, Guadalupe; Vergara-Castañeda, Haydé A.; Oomah, B. Dave (September 2015). "Spent coffee grounds: A review on current research and future prospects". Trends in Food Science & Technology. 45 (1): 24–36. doi:10.1016/j.tifs.2015.04.012.
  6. ^ Choi, Bogyoung; Koh, Eunmi (August 2017). "Spent coffee as a rich source of antioxidative compounds". Food Science and Biotechnology. 26 (4): 921–927. doi:10.1007/s10068-017-0144-9. PMC 6049539. PMID 30263620.
  7. ^ Murthy, Pushpa S.; Madhava Naidu, M. (September 2012). "Sustainable management of coffee industry by-products and value addition—A review". Resources, Conservation and Recycling. 66: 45–58. doi:10.1016/j.resconrec.2012.06.005.
  8. ^ Kamil, Mohammed; Ramadan, Khalid Mustafa; Awad, Omar I.; Ibrahim, Thamir K.; Inayat, Abrar; Ma, Xiao (July 2019). "Environmental impacts of biodiesel production from waste spent coffee grounds and its implementation in a compression ignition engine". Science of the Total Environment. 675: 13–30. doi:10.1016/j.scitotenv.2019.04.156. PMID 31026637. S2CID 135449537.
  9. ^ Gebreeyessus, Getachew Dagnew (August 2022). "Towards the sustainable and circular bioeconomy: Insights on spent coffee grounds valorization". Science of the Total Environment. 833: 155113. doi:10.1016/j.scitotenv.2022.155113. PMID 35427619. S2CID 248138300.
  10. ^ a b c "Don't Throw Out Your Leftover Coffee Grounds!". Huffington Post. 4 August 2014. Retrieved 25 December 2014.
  11. ^ Martin, Deborah L; Gershuny, Grace, eds. (1992). "Coffee wastes". The Rodale book of composting. Emmaus, PA: Rodale Press. p. 86. ISBN 978-0-87857-991-4. Retrieved 5 January 2010.
  12. ^ a b "Coffee Grounds Perk up Compost Pile With Nitrogen". Life at OSU. 10 June 2009. Retrieved 1 April 2018.
  13. ^ Liu, K.; Price, G.W. (September 2011). "Evaluation of three composting systems for the management of spent coffee grounds". Bioresource Technology. 102 (17): 7966–7974. doi:10.1016/j.biortech.2011.05.073. PMID 21704514.
  14. ^ Stylianou, Marinos; Agapiou, Agapios; Omirou, Michalis; Vyrides, Ioannis; Ioannides, Ioannis M.; Maratheftis, Grivas; Fasoula, Dionysia (December 2018). "Converting environmental risks to benefits by using spent coffee grounds (SCG) as a valuable resource". Environmental Science and Pollution Research. 25 (36): 35776–35790. doi:10.1007/s11356-018-2359-6. PMID 29860699. S2CID 44081836.
  15. ^ Southern Cultivator. J.W. & W.S. Jones. 1853.
  16. ^ "NORTH COAST GARDENING: Winter vegetable growing". Eureka Times-Standard. 24 December 2014. Retrieved 25 December 2014.
  17. ^ a b Chalker-Scott, Ph.D, Linda (2009). "Coffee grounds— will they perk up plants?" (PDF). Master Gardener. Puyallup Research and Extension Center, Washington State University. Retrieved 25 December 2014.{{cite web}}: CS1 maint: multiple names: authors list (link)
  18. ^ "Coffee for Your Plants? Starbucks Offers Free Coffee Grounds for Gardeners". Starbucks.com. Retrieved 13 December 2015.
  19. ^ "About Us | Coffee Grounds to Ground". Groundtoground.org. Retrieved 26 October 2011.
  20. ^ "Green Coffee Shop Scheme". Cambridge Food Hub. 8 May 2019. Retrieved 25 October 2019.
  21. ^ "DPG Media Privacy Gate". myprivacy.dpgmedia.be.[failed verification]
  22. ^ "PermaFungi |".
  23. ^ Mussatto, Solange I.; Machado, Ercília M. S.; Martins, Silvia; Teixeira, José A. (July 2011). "Production, Composition, and Application of Coffee and Its Industrial Residues". Food and Bioprocess Technology. 4 (5): 661–672. doi:10.1007/s11947-011-0565-z.
  24. ^ The Universal Household Assistant: A Cyclopedia of what Everyone Should Know... A.L. Burt. 1884. p. 347.
  25. ^ Vandeponseele, Alexandre; Draye, Micheline; Piot, Christine; Chatel, Gregory (2 April 2021). "Study of Influential Parameters of the Caffeine Extraction from Spent Coffee Grounds: From Brewing Coffee Method to the Waste Treatment Conditions". Clean Technologies. 3 (2): 335–350. doi:10.3390/cleantechnol3020019.
  26. ^ Yamane, Koji; Kono, Mitsuaki; Fukunaga, Taiji; Iwai, Kazuya; Sekine, Rie; Watanabe, Yoshinori; Iijima, Morio (January 2014). "Field Evaluation of Coffee Grounds Application for Crop Growth Enhancement, Weed Control, and Soil Improvement". Plant Production Science. 17 (1): 93–102. doi:10.1626/pps.17.93. S2CID 84273209.