Physical and mechanical methods of extraction from ground coffee and spent coffee ground

Coffee, one of the most popular beverages in the world, is consumed by millions of people every day. The result in the cup is strongly affected by the extraction method, and many papers have focused on this subject. In recent decades, various coffee-based beverages, obtained using different extraction techniques have entered the market, but there aren’t reported in the scientific literature. During the preparation of a coffee beverage, a solid residue known as spent coffee grounds (SCG) is produced. In recent years, however, the growing awareness of the necessity for waste reduction and environmental protection has stimulated the search for possible methods of using this waste (Kondamudi 2008), (Adi 2009), (Fenoll 2011), (Janissen and Huynh 2018). The aim of the work was at first, to characterize and compare eight different coffee extraction methods from a physical and chemical point of view, starting from the same raw material. The study describes, three types of Espresso, Moka, French Press, and three filter coffee that for the first time are reported in the scientific literature Cold Brew, V60, and Aeropress. After, the attention was focused on cold extraction: cold brew and cold drip. The effects of the primary process variables (temperature and contact time) were assessed in a full factorial experiment. Finally, the focus of the third study concern to test which variables could influence the amounts of phytochemicals extracted, to optimize a green extraction method for water-soluble compounds that do not require the use of organic solvents and that maximizes the recovery of phytochemicals from spent coffee grounds (SCG). We used a Plackett-Burman design to estimate which factors have more influence on the amount of phytochemicals to be recovered. In the second part of the experiment, we have tested only the significant factors with a fully factorial scheme. For each study has been performed physical measurements included the quantification of TDS, density, pH. Furthermore, the phytochemicals have been quantified using HPLC-DAD. Technical differences in these 8 extraction methods led to quantitative differences in the extraction and produced coffees with different profiles. Maximum caffeine and CGA concentrations were found in Espresso coffees, while Moka and filtered coffees were three to six times less concentrated. The Espresso method was most efficient for caffeine and CGA recovery. Per-cup caffeine and CGAs were higher in Cold Brew than Espresso coffees, as a function of the volume of the beverage. Concerning the cold extraction techniques, significant differences were found in the chemical and physical parameters, both between and within the two methods. The temperature was found to increase the concentrations of several compounds. Conversely, the contact time between the coffee powder and water has a limited effect on brew characteristics. Regarding the study of the recovery of phytochemicals, the results obtained from the fractional design showed that the significant factors to recover phytochemicals were Temperature and type of SCG. Afterward, four temperature and two types of SCG have been tested. At 110°C has been observed the higher concentration values of caffeine and CGAs. Moreover, a significant effect was revelated for a different type of SCG. The amounts of phytochemicals recovered from SCG was significantly higher in French Press than the Espresso. These conditions of temperatures could be considerate mild conditions, combined with the use of water as a solvent. The system of recovery was demonstrated to be an efficient method with the added value of being a green and low-cost system.