Asymptotic analysis of the dominant mechanisms in the coffee extraction process

peer-reviewedExtraction of coffee solubles from roast and ground coffee is a highly complex process, depending on a large number of brewing parameters. We consider a recent, experimentally validated, model of coffee extraction, describing extraction from a coffee bed using a double porosity model, which includes dissolution and transport of coffee. It was shown that this model can accurately describe coffee extraction in two situations: extraction from a dilute suspension of coffee grains and extraction from a packed coffee bed. Despite being based on some simplifying assumptions, this model can only be solved numerically. In this paper we consider asymptotic solutions of the model describing extraction from a packed coffee bed. Such solutions can explicitly relate coffee concentration to the process parameters. For an individual coffee grain, extraction is controlled by a rapid dissolution of coffee from the surface of the grain, in conjunction with a slower diffusion of coffee through the intragranular pore network to the grain surface. Extraction of coffee from the bed also depends on the speed of advection of coffee from the bed. We utilize the small parameter resulting from the ratio of the advection timescale to the grain diffusion timescale to construct asymptotic solutions using the method of matched asymptotic expansions. The asymptotic solutions are compared to numerical solutions and data from coffee extraction experiments. The asymptotic solutions depend on a small number of dimensionless parameters and so are useful to quickly fit extraction curves and investigate the influence of various process parameters on the extraction.PUBLISHEDpeer-reviewe

Le pavimentazioni in seminato nell’edilizia storica cremonese

XVIII convegno internazionale Scienza e beni culturali, Bressanon

Public finances in EMU

The optimism of the Spring that the European economy is emerging into the post-crisis world has become more cautious. The report provides an overview of the current developments, looking at recent outcomes and both the Commission services' and the Member States' own projections for the public finances. This provides the background to discuss the proposed reform to economic and budgetary surveillance which is currently nearing the end of the adoption process and which seeks to put into action the main lessons learnt from the crisis. The report discusses the various parts of the reform in details, looking at the changes to the Stability and Growth Pact (SGP), as well as the other proposals which accompany it and are key to an integrated policy change. It shows how the reform package addresses the weaknesses identified by the crisis, both in terms of the setting of policy and the correction of deviations from the optimal path