The influence of extraction parameters on spent coffee grounds as a renewable tannin resource

• The reuse of spent coffee grounds as a renewable resource for tannin isolation was demonstrated in the current study.
• Comprehensive models were established for the tannin extraction process.
• Changing trends of different extraction conditions were demonstrated.
• The influence of each extraction parameter on the extracted tannin is discussed in detail.
• Spent coffee ground tannin was extracted at an acceptable yield without sacrificing its reactivity under optimization.

Spent coffee grounds that are left behind during the coffee brewing process consist of valuable tannin compounds which makes them ideal material as a renewable tannin resource. For this reason, the concept of cleaner production had been applied in practice and a tannin extraction process with spent coffee grounds as raw material was investigated in the present study. Among the extraction key factors, namely sodium hydroxide concentration, extraction temperature, liquid to solid ratio, and extraction time, the former three factors had exerted a considerable effect on spent coffee ground tannin extraction yield and its reactivity. However, extraction time had only marginal effects which could be simply neglected in the tannin extraction process. These observations imply that spent coffee grounds can be reused as a renewable tannin resource by properly selecting the extraction parameters in order to produce the spent coffee ground tannin with desirable extraction yield and reactivity. By taking both the spent coffee ground tannin extraction yield and reactivity into consideration, the optimum extraction conditions are; 5% sodium hydroxide concentration, 100 °C extraction temperature, 30 min extraction time, and 8.23 liquid to solid ratio, so that tannin with a high extraction yield (21.02%) and high reactivity (29.69%) could be recovered. The present study provides an understanding on the impact of the extraction parameters on isolated spent coffee ground tannin as well as to fill up academic deficiencies in spent coffee grounds, which, in turn, could serve as a reliable guideline for the development of a full-scale, sustainable spent coffee ground tannin extraction process in coffee industries.