Used coffee grounds

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Used coffee grounds
Used coffee grounds in boxes.
Usage

Used coffee grounds is the result of brewing coffee, and are the final product after

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

See also: Composition of coffee beans

Most used coffee grounds are similar in chemical composition, although coffee grounds used to make instant coffee have fewer chemicals in them due to a more extensive extraction process.[2] Used coffee grounds are rich in sugars,[3] which comprise about half of their weight. A further 20% is made up of proteins, and a further 20% is lignins.[4] The dry coffee grounds contain significant amounts of potassium (11.7 g/kg), nitrogen (27.9 g/kg), magnesium (1.9 g/kg), and phosphorus (1.8 g/kg).[5] The quantity of caffeine remaining in used coffee grounds is around 48% of that in fresh coffee grounds.[6] There are significantly less tannins in used coffee grounds than fresh coffee grounds.[7]

Production

On average, 1 tonne of

green coffee produces approximately 650 kg of spent coffee grounds,[8] and over 15 million tonnes of spent coffee grounds are generated annually.[9] In keeping with a life cycle approach to sustainability,[10] 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.[6]

Usage

Precautions

It is not recommended to burn dried used coffee grounds, as they give off hazardous

nitrogen oxides when burnt.[4]

In gardens

Composting worms
moving about in used coffee grounds.

In gardens, coffee grounds may be used for

phytotoxic properties which can be reduced through composting.[15] Gardeners have reported the use of used coffee grounds as a borer,[16] slug and snail repellent,[11][17] but this has not yet been scientifically tested.[18] Some commercial coffee shops run initiatives to prevent the grounds from going to waste, including Starbucks' "Grounds for your Garden" project,[19] and community sponsored initiatives exist, such as "Ground to Ground" [20] or the 'Green Coffee Shop Scheme' in Cambridgeshire, UK.[21]

In fortune telling

Main article: Tasseography

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

In the home

Dried used coffee grounds were recommended to fill

air fresheners, and body soap scrubs.[11]

Agricultural uses

Oyster mushroom mycelium on coffee grounds.

Initiatives have succeeded using coffee grounds as a substrate for the cultivation of mushrooms (including oyster mushrooms).[23][24] 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.[6]

Application of 10 kg used coffee grounds per square metre has been suggested as part of a

horse manure at the same time as the coffee grounds has been shown to nearly eliminate negative effects of fresh used coffee grounds.[25]

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.[26]

Industrial uses

Coffee grounds may be used industrially in

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.[4]

Biodiesel may be produced from coffee grounds, either directly by extracting the oils using solvents,[27] by mixing the grounds with methane and a catalyst,[28] or by using the grounds to feed bio-producing algae.[29]

In concrete making, 10-15% of the sand used may be replaced with used coffee grounds.[30]

It has been suggested to recover caffeine from used coffee grounds for commercial applications in

pharmaceutic industries.[31]

In 2021, Gloucestershire-based football club Forest Green Rovers trialed a kit made from 35% used coffee grounds combined with recycled plastic.

See also

References

  1. ISBN 978-0-465-02404-9
  2. ISSN 2073-4395
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  3. hdl:1822/16744
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  4. ^
    S2CID 104298839
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  5. S2CID 38776511
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  6. ^
    doi:10.1016/j.tifs.2015.04.012
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  7. PMID 30263620
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  8. doi:10.1016/j.resconrec.2012.06.005
    .
  9. S2CID 135449537
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  10. S2CID 248138300
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  11. ^ a b c "Don't Throw Out Your Leftover Coffee Grounds!". Huffington Post. 4 August 2014. Retrieved 25 December 2014.
  12. ISBN 978-0-87857-991-4
    . Retrieved 5 January 2010.
  13. ^ a b "Coffee Grounds Perk up Compost Pile With Nitrogen". Life at OSU. 10 June 2009. Retrieved 1 April 2018.
  14. PMID 21704514
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  15. S2CID 44081836
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  16. ^ Southern Cultivator. J.W. & W.S. Jones. 1853.
  17. ^ "NORTH COAST GARDENING: Winter vegetable growing". Eureka Times-Standard. 24 December 2014. Retrieved 25 December 2014.
  18. ^ a b Chalker-Scott, Linda (2009). "Coffee grounds— will they perk up plants?" (PDF). Master Gardener. Puyallup Research and Extension Center, Washington State University. Retrieved 25 December 2014.
  19. ^ "Coffee for Your Plants? Starbucks Offers Free Coffee Grounds for Gardeners". Starbucks.com. Retrieved 13 December 2015.
  20. ^ "About Us | Coffee Grounds to Ground". Groundtoground.org. 24 May 2010. Retrieved 26 October 2011.
  21. ^ "Green Coffee Shop Scheme". Cambridge Food Hub. 8 May 2019. Retrieved 25 October 2019.
  22. ^ The Universal Household Assistant: A Cyclopedia of what Everyone Should Know... A.L. Burt. 1884. p. 347.
  23. ^ Dillen, Nina (18 June 2015). "Zelf oesterzwammen kweken op basis van ... koffiegruis? Zo doe je dat". Het Laatste Nieuws. Archived from the original on 21 April 2021. Retrieved 7 November 2023.
  24. ^ "PermaFungi |". 28 March 2014.
  25. S2CID 84273209
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  26. S2CID 27800545
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  27. ISSN 0021-8561
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  28. ^ Patel, Prachi (18 May 2017). "A simpler route to biodiesel from used coffee grounds". Anthropocene. Retrieved 9 October 2023.
  29. ^ Coxworth, Ben (2 November 2022). "Coffee grounds used to both feed and support biodiesel-producing algae". New Atlas. Retrieved 9 October 2023.
  30. ^ Christie, Damian (31 October 2019). "From coffee to concrete: Researchers offer a new solution". Quarry.
  31. doi:10.3390/cleantechnol3020019
    .
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