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The resulting water, which now contains the caffeine and any flavor compounds that dissolved out from the beans, gets passed through activated charcoal filters.

Researchers from the University of Cambridge used a method similar to charging a battery to instead charge activated charcoal, which is often used in household water filters.

This green coffee extract is passed through activated charcoal filters, which trap the caffeine molecules while allowing the flavours to pass through.

Prof Oberholster says there are some filtration techniques, like reverse osmosis, and treatments involving activated charcoal which are already used to remove bitter compounds from wine.

The school system has also placed activated charcoal filters designed to trap gases on the mechanical equipment.