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Physics in food and drink manufacturing case study: Coffee

Image: Shutterstock/iravgustin
Image: Shutterstock/iravgustin

Physicists can apply much of their skillset to food manufacturing: their ability to analyse problems, bringing clarity to a problem statement, establishing the basic principles and governing equations, and breaking a problem down and estimating what is important.

They can focus on pinch-points in a process, involving complex physical transformations. Physicists bring strong equation-based modelling skills, can make rational estimates, and, furthermore, are trained to develop and apply new measurement techniques. In particular, physics training brings a broad view, and physicists can adapt models and knowledge developed from seemingly unrelated areas to their current food problem.

As you drink your morning coffee you may wonder what the role of physics is in this beverage product. There is plenty. Much of the roasting of coffee is a mystery. In particular, the evolving physical condition inside the roasting bean sees much myth but little hard evidence. Although some may like to keep it as an art, we, as physicists and commercial operations seeking to optimise raw material and energy-use, need a deeper understanding. A collaboration with the University of Oxford lead us to new models of moisture and pressure conditions inside a roasting bean – models inspired by ones developed for baking bread.

Coffee is brewed by flowing through a packed bed of particles – the complex physics of flow through such beds, the permeability of the bed and the packing of grains are rich areas of intriguing micron-scale physics. The coffee bed is not in a steady state – on the timescale of brewing, it evolves. The flow passing through it is multi-phase, the beverage liquid but also gas; coffee grains are 50% air, which is released into the flow when they are wetted. At Jacobs Douwe Egberts, we’ve developed controlled experiments on measuring the evolution of the flow resistance of the bed, and novel theory on the packing of the grains. We’ve found new insights into the effects of fining agents on particle packing and dynamic bed permeability. We’ve used nuclear magnetic resonance at the University of Cambridge to image flows through beds. The work is relevant to the individual brewing we all do at home in modern, on-demand coffee systems but also the industrial-scale processing of instant coffee. In the latter case, there are intriguing questions of the resulting granule structure on drying the extract, how its interconnected pores space promotes the fast dissolution of the granule. This was the goal of a recent collaboration with the University of Birmingham funded by Innovate UK.

While this is all developed for coffee, we’ve exploited developments in physics from other areas, particularly those in which flow through porous beds is central, such as the oil and gas industry. We hope in turn that, when published, some of our new ideas may be useful elsewhere. Beyond these examples, coffee beverage manufacturing is replete with problems on the flow of powders, the creation of metastable states, and the evolution of foams and colloid structures.

  • This an extract from the IOP report The Health of Physics in UK Food Manufacturing, due to be launched at PepsiCo on 21 October. Follow the launch event on Twitter.
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John Melrose

John Melrose

Dr John Melrose is strategic process and technology manager at Jacobs Douwe Egberts
John Melrose

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