Graphene oxide membrane removes caffeine from brewed coffee while keeping flavor compounds

The useful part

(Nanowerk News) The humble coffee filter has the relatively simple job of letting the coffee through and leaving the grounds behind. They published their research in Journal of Membrane Science ("Multi-criteria evaluation of graphene oxide nanofiltration membranes for decaffeination"). Removing caffeine while leaving the things that make coffee taste like coffee means distinguishing between molecules at an extraordinarily small scale.

How it works

• For UNSW Team Graphene master's research student Yihan Tian, the challenge had plenty of appeal.
• "What attracted me most is that this research connects fundamental membrane science with a very practical, everyday product," she said.
• Working alongside Dr Tongxi Lin and COE-CSI research fellow Dr Xiaojun Ren, Tian developed a membrane using graphene oxide.
• Finding the right balance The researchers produced several versions of the membrane, but quickly encountered another problem: making a membrane better at one thing could make it worse at another.
• Promising progress Removing around half of the caffeine is an encouraging result, while further work is still needed to move towards a practical decaffeination process.

What to take from it

Future work on cleaning, reuse and membrane lifetime could help maintain performance for longer, while larger-scale trials could establish the costs of running the process. The technology has significant potential for industry applications in the coffee and broader food and beverage sector. Removing as much caffeine as possible, for example, is of little use if the membrane also removes too many of the compounds you want to keep.

Example or evidence

• Removing around half of the caffeine while retaining several other coffee compounds gives the researchers a promising starting point for further development.
• The researchers also plan to explore how filtration affects coffee's taste and nutritional properties.
• From the laboratory to something larger The researchers have also taken an early step towards exploring how the approach could work at a larger scale.
• Hollow fibres are already used in commercial filtration systems, giving the researchers an established membrane format to build on as they develop the technology towards practical use.

Details worth keeping

Tiny channels between those layers allow water and other molecules to pass through the membrane and, by incorporating sodium alginate and crosslinking it with calcium ions, the researchers were able to change those channels and influence which molecules could make their way through. In effect, they created an extraordinarily fine sieve. Rather than simply asking which membrane removed the most caffeine, the researchers assessed them against several measures—including caffeine removal, retention of selected compounds and water permeance—to identify the best overall performer.

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