The hidden value of Spent Coffee Ground

Beyond the espresso – The hidden value of spent coffee ground

If you are like me what drives you to get up in the morning is the thought of the cold breakfast pizza, wisely saved from the previous dinner. Only to discover that your sister’s boyfriend finished it when they come home the night before.

Then if you are again like me or like one of the billions of coffee consumer around the world (an estimate of 151.3 million 60 kg bags of coffee was consumed from Oct. 2015 to Sep. 2016, and the figures are increasing [14]) you turn, disappointed, but not yet defeated, to the espresso machine to get an energizing cup of creamy coffee, with a drop of cold milk (that’s how I like it and I don’t care if it’s not the best way to taste it) to start the day.

Most people would say that they wake up to the smell of freshly brewed coffee (which has apparently some truth to it[29]), but the first smell I personally notice is the earthy smell of exhausted coffee grind of the previous brews from the handle. It is still appealing with its warm smell and appereance.

Spent Coffee Grounds
You can smell the earthy perfume of coffee grounds, just by looking at this, can’t you?

So every morning it felt a little bit bad throwing it away. therefore I searched for alternative ways of using this that are technically called “Spent Coffee Grounds” or SCG, so I found some useful tips around the web, like, for example, this recipe for a coffee body scrubs.

But even if I want a sexy smooth skin for the summer, with an average of 4 cups of espresso a day (here is my math if you are interested), a reserve of ~1.5kg of scrubs per month seems a little too much. I will arrive at the beach as just a sexy shiny skeleton!

Many home-friendly solutions can be found online such numerous applications in the garden as compost and fertilizer and other cosmetic uses, but since the sheer quantity of coffee used every day (coffee is notoriously the second commodity exchanged [20] and one of the most drank beverage in the world) these solutions fell a lot short in tackling the issue of coffee waste.

So I turned to the scientific community to discover what are the latest news on the matter.

Coffee production and waste.

I focused this article on product-specific waste, generated in the process of creating this black stuff that allows us to wake in the morning and more specifically on SGC. There are different kinds of waste created in the production of roasted coffee, all of them with some valuable properties for a profitable reuse:

  1. Coffee Pulp & Coffee Husk:

    The by-product generated to obtaining the green (unroasted) coffee bean represents around 45-50% of the whole coffee fruit dry matter[27], most of which is produced during post-harvesting operations. The results of these operations are called Pulp or Husk, depending on the method used to retrieve the green beans, respectively wet (which involve various phase including fermentation. It is used mainly for the arabica cultivar and is deemed a more refined process and influence taste and price[2]) and dry (a simpler and cheaper method).

    This Coffee pulp is essentially rich in carbohydrates, proteins and minerals (especially potassium) and it also contains appreciable amounts of tannins, polyphenols and caffeine[8], which can be extracted and then purified using superficial CO2  fluid extraction or superheated water extraction[20].

  2. Silverskin:

    It is the layer that covers the actual coffee bean and it is collected during the roasting process [27,3] and, even if it is a smaller portion of the waste produced (the ratio between the mass of silverskin produced and the mass of the saleable substance goes from 0.02 to 0.04[27]) this could still present a hazard to environment and a missed  opportunity if not recovered, because silverskin could find a similar useful industrial application as SGC[2], which are analysed below.

  3. Spent ground Coffee:

    It is quite complex to quantify the actual volume of the SCG actually wasted between homemade coffee, coffee shops and bars daily consumption, thus is difficult collecting and retrieving data about the actual amount that goes wasted every day. It is estimated, however, that around 50% of the entire coffee production is used by the dried coffee industry, which in turn generates 6 million tonnes of SGC annually![2], thus making this specific sector the focus of most research. This is relevant also because the SGC made available could remain inside the industrial process without being dispersed

    Spent Coffee Ground Composition
    Different coffee cultivars (arabica vs robusta), as well as different methods of production and preparation, yields different composition of the SCG.

Spent Ground Coffee

The reuse of a such widely accessible resources has sparked an increasing interest in researchers to find viable ways to reinsert the SCG in the production cycle with added value.

Without going into too much detail SCG chemical composition yields great potential for various application. SCG are composed mainly of carbohydrates (mostly sugars)[2, 22,30]. Other significant components present are protein and minerals [2, 22]. SCG are also an important source of insoluble dietary fibre, antioxidants and essential amino acids [19]

Dired Spent Ground Coffee
The dried coffee industry uses 50% if the entire coffee production and it generates 6 million tonnes of SGC annually!!

In the relevant literature, several applications have been described for SCG, specifically:

1. As Biofuels

This is the main field of research when we talk about SCG reprocess.

The chemical composition of SCG reveals that they are a viable candidate for the production of bioethanol and biodiesel.

Extraction of oil from SCG, used in the production of biodiesel (100% conversion of oil to biodiesel), yields 10-15% oil depending on the coffee species (Arabica or Robusta).[16,8]

The presence of high concentrations of palmitic and stearic acids in the lipophilic extracts would justify further investigation on biodiesel production based on coffee wastes. [25]

2. As Composts

The feasibility of using SGC to provide some nutrients to the soil is well documented and also recommended as an effective ingredient in composting. SCG directly composted in the soil, increasing the plant chlorophylls and carotenoids levels, and increasing the presence of nutritional minerals, specifically potassium, phosphorous and sodium. [2,3]

Another agricultural application of SCG is being a prolific cultivation media for various mushrooms species [11, 14,32].

3. As Animal Feed

SGC can be a rich source of nutrient and bioactive compound[1] and can be used to enhance the performance of animal feed. However, the presence of caffeine and tannins (2-4.5%)  limits their use to small quantities as larger concentration could affect the health of the livestock and also making it less palatable to the animals. So it should be incorporated in a certain proportion (different from animal to animal) or otherwise through some process (chemical extraction, microbial treatment, or fermentation) apt to decrease the amount of these compounds, but thus increasing the cost of such resource.[3,20,32,16]

4. As Biosorbents

this is where things get more interesting. SCG have a good absorption potential. experiments have been carried out revealing that spent coffee grounds are suitable candidates for use as adsorbents in the removal of dyes from water, such as Methylene Blue [11], and others xenobiotics, when magnetically charged by magnetic fluid treatment[28]

Other researchers have highlighted the suitability of SGC of removing potentially harmful metal, such as lead[31] and mercury ions, especially when combined with silicon and sugars to create an absorbent foam.[7]

5. As Food Ingredient

Using the SCG in the formulation of innovative food product, focusing on healthy products formulation, is personally the most interesting development.

Aromatic compounds and flavours extracted from SCG can be reused as natural ingredients in the formulation of health and functional products. An attempt to evaluate the possibility of directly reuse this by-products as food ingredient in innovative bakery products, showed the potential added functional value, for a low cost, of incorporating SCG, in small quantity, as natural source of antioxidant insoluble dietary fibre, proteins, essential amino acids, carotenoids[24], and low glycaemic sugars, satisfying the consumers’ wish for low-cal snacks. [19,6]

A Spent Coffee Ground, to go, please!

The feeling of guilt that I have been experiencing in the morning for a while now, deciding between throwing away the SCG or keeping it to make a bucketload of skin scrubs, it is, in fact, well-grounded.  Some plans are already been devised to reduce and reuse the dried coffee industry waste, which is collected by specialised agencies. For example, Nestlè has launched an internal program to significantly reduce and reuse coffee waste in its factory in Europe by 2020[6].

Spent Coffee Waste Value
This is not just a cup of coffee, but it could become a pot of feedstock gold.

What is still unclear is the economic fitness of some of these solutions and which actions can be put in motion to intercept all the waste that is produced in household and venues (cafes and bars) that still are not organised in this field.

Think about it nex time you are enjoying your Barista Coffee!


Gianlorenzo De Santis

SUGGESTED READ: John L. Massey, Coffee: Production, Consumption and Health Benefits,   2016, Nova Publisher Ltd.


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