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 Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting ...

. 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 An adulterant is caused by the act of adulteration, a practice of secretly mixing a substance with another. Typical substances that are adulterated include but are not limited to food, cosmetics, pharmaceuticals, fuel, or other chemicals, that ...

pure coffee.

Chemical composition

Used coffee grounds are rich in sugars, which comprise about half of their weight. A further 20% is made up of proteins, and a further 20% is lignins. 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). The quantity of caffeine remaining in used coffee grounds is around 48% of that in fresh coffee grounds. There are significantly less

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'', ...

s in used coffee grounds than fresh coffee grounds.

Production

On average, 1 tonne of green coffee produces approximately 650 kg of spent coffee grounds, and over 15 million tonnes of spent coffee grounds are generated annually. In keeping with a life cycle approach to sustainability, 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.

Usage

In gardens

In gardens, coffee grounds may be used for

compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical and biological properties. It is commonly prepared by decomposing plant, food waste, recycling organic materials and manure. The resulting m ...

ing or as a

mulch A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving fertility and health of the soil, reducing weed growth and enhancing the visual appeal of the area. A ...

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 Blueberries are a widely distributed and widespread group of perennial flowering plants with blue or purple berries. They are classified in the section ''Cyanococcus'' within the genus ''Vaccinium''. ''Vaccinium'' also includes cranberries, b ...

, although due to acids being leached from the grounds while in use, they typically have a neutral pH, and

red wiggler ''Eisenia fetida'', known under various common names such as manure worm, redworm, brandling worm, panfish worm, trout worm, tiger worm, red wiggler worm, etc., is a species of earthworm adapted to decaying organic material. These worms thrive i ...

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. Used coffee grounds are particularly noted as a

soil amendment A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...

. Spent coffee grounds have

phytotoxic Phytotoxins are substances that are poisonous or toxic to the growth of plants. Phytotoxic substances may result from human activity, as with herbicides, or they may be produced by plants, by microorganisms, or by naturally occurring chemical react ...

properties which can be reduced through composting. Gardeners have reported the use of used coffee grounds as a borer, slug and snail repellent, but this has not yet been scientifically tested. Some commercial coffee shops run initiatives to prevent the grounds from going to waste, including

Starbucks Starbucks Corporation is an American multinational chain of coffeehouses and roastery reserves headquartered in Seattle, Washington. It is the world's largest coffeehouse chain. As of November 2021, the company had 33,833 stores in 80 cou ...

' "Grounds for your Garden" project, and community sponsored initiatives exist, such as "Ground to Ground" or the 'Green Coffee Shop Scheme' in Cambridgeshire, UK. Restos de café para adivinar

Use in fortune telling

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

Other uses

Oyster mushroom (Pleurotus ostreatus) mycelium on coffee grounds

Initiatives have succeeded using coffee grounds as a substrate for the cultivation of mushrooms (including

oyster mushrooms ''Pleurotus'' is a genus of gilled mushrooms which includes one of the most widely eaten mushrooms, '' P. ostreatus''. Species of ''Pleurotus'' may be called oyster, abalone, or tree mushrooms, and are some of the most commonly cultivated edib ...

). 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. Used coffee grounds have other homemade uses in

wood staining Wood stain is a type of paint used to colour wood and consists of colourants dissolved and/or suspended in a 'vehicle' or solvent. Vehicle is the preferred term, as the contents of a stain may not be truly dissolved in the vehicle, but rather ...

air fresheners Air fresheners are consumer products that typically emit fragrance and are used in homes or commercial interiors such as restrooms, foyers, hallways, vestibules and other smaller indoor areas, as well as larger areas such as hotel lobbies, auto ...

, and body soap scrubs. They may also be used industrially in

biogas Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...

production or to treat wastewater.

Bioethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a h ...

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. 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. 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. Dried used coffee grounds were recommended to fill

pincushion A pincushion (or pin cushion) is a small, stuffed cushion, typically across, which is used in sewing to store pins or needles with their heads protruding to take hold of them easily, collect them, and keep them organized. Pincushions are typi ...

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

agrifood The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditional, ...

, cosmetic, nutraceutic or

pharmaceutic Pharmaceutics is the discipline of pharmacy that deals with the process of turning a new chemical entity (NCE) or old drugs into a medication to be used safely and effectively by patients. It is also called the science of dosage form design. The ...

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

crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...

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 A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock for ...

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.

References

{{Coffee Coffee derivatives Horticulture Composting Food waste