Thursday, November 17, 2016

What We're Reading

As I told Leonard Cohen just last week: I want it darker.

Extraction 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.


geonni banner said...

That makes my head hurt...

PipedreamFarm said...

That description is too simplified for brewing coffee (or tea). "Coffee" ("tea") is a complex mixture of water soluble chemicals in differing amounts and each has differing extraction rates from the solid (preprocessed bean or tea leaf) depending upon water temperature.

If you want to get as much extracted from the grind as possible you need to take the next step beyond a percolator. Instead of splashing the hot water/weak coffee through the grind you need to boil the hot water (leaving most of the extracted chemicals in the pot), then cool the steam and let the distilled water extract more from the grind.

Use a refluxing extractor.

PBurns said...

Yeah baby. But you have to be careful with temperature, as the temperatures used in a reflux extractor can burn the roast. The more I drink and know, the more I think COLD BREW is the answer.