1. Introduction
In particular, the coffee extraction process can yield substances that are useful for the production of biofuels and other high-value-added products. Coffee consists of caffeine, organic acids, polyphenols, vitamins, minerals, lipids, carbohydrates, and about 700 volatile compounds that determine its aroma and flavor. Extraction is a chemical technique used to isolate a component from the same starting substance. For example, caffeine can be extracted from coffee to produce decaffeinated coffee.
My note: I want to make it clear that this article is not intended to be a standalone scientific study. Through this blog, I hope to carefully share scientifically relevant information. If you’d like to explore this topic in greater depth, I invite you to refer to the links to the scientific research that I’m sharing here so you can analyze all the results.
2. Focus of the study
The study, conducted by a team from Rovira i Virgili University (URV), focuses on extracting oil from coffee grounds while keeping the plant matter intact, as it can be used in other processes.
3. Importance of the study
The International Coffee Organization (ICO) states that 40 million metric tons of coffee waste are produced annually. This immense amount of waste can be used in various sustainable ways to reduce environmental impact. It can be turned into natural fertilizers, natural detergents, natural repellents, oil, and many other biomaterials. The waste contains about 15% lipids (fats), a key component in the production of biodiesel, for example. Biodiesel stands out as a biodegradable and low-emission alternative. However, its economic viability is strictly constrained by feedstock costs, requiring of abundant and low-cost lipid-rich residues to be feasible.
3. Techniques
Coffee grounds were collected along a single morning, and it exhibited an initial moisture content of approximately 50 % (w/w). To inhibit microbial proliferation during storage, the moisture content was reduced to less than 10 % by drying the material the same day of collection in a convection oven at 40 °C for 72 h. The lipid content was determined by Soxhlet extraction using n-hexane. Soxhlet is a laboratory technique widely used as a point of reference because it offers high yields but requires more time and energy and is less suitable for industrial applications. Approximately 6 g of sample were placed in a cellulose thimble and extracted under reflux in a 100 mL Soxhlet apparatus connected to a 500 mL round-bottom flask containing 210 mL of hexane, corresponding to a solvent-to-biomass ratio of 35 mL g−1. Extraction was conducted for 24 h at a cycling rate of approximately six cycles per hour, a duration widely accepted to provide exhaustive lipid extraction from lignocellulosic matrices. The recovered oil was further dried at 105 °C for 6 h to ensure complete removal of residual solvent. The defatted spent coffee grounds (DFSCG) were dried at 60 °C to eliminate traces of hexane.
WDSCG is the initial dry mass of biomass; WFE is the mass of the flask containing the extract; WF is the mass of the empty flask.
4. Condition of experiment
The optimal conditions are at 45°C for 60 minutes with a ratio of 35 milliliters of n-hexane per gram of dry residue. With these parameters, the process can recover approximately 90% of the amount of oil that can be obtained with Soxhlet. The optimized process yielded an oil with a very low impurity content of 0.3%.
5. Results
Photo from Systematic evaluation of batch hexane extraction as a scalable pretreatment for the comprehensive valorization of spent coffee grounds – ScienceDirect. Contour map matrix of DSCG extraction yield across the experimental space, with one extraction variable fixed per row.
The topography of the response surfaces evidenced an internal maximum in the region of 45 °C, 35 mL g−1, and 60 min.
Among the main effects, temperature emerged as the dominant factor, followed by extraction time and, to a lesser extent, the R ratio (hexane/biomass). The pronounced effect of temperature may be attributed to the simultaneous enhancement of lipid solubility and molecular diffusivity, thereby fostering mass transfer processes. For its part, the extraction time reflects the progressive approach toward system equilibrium, whereas the R ratio modulates the concentration gradient that impels the extraction.
Bibliographic sources For more info Systematic evaluation of batch hexane extraction as a scalable pretreatment for the comprehensive valorization of spent coffee grounds – ScienceDirect
Thank you for reading
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