Millimetre-sized robots made of iron oxide and packed with yeast speed up fermentation of beer by swimming around in the fermenting container and can be removed with a magnet, eliminating the need for filtering out yeast.
Tiny robots packed with yeast speed up the fermentation of beer and eliminate the need to filter it before bottling.
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| Beer fermentation vats Shutterstock/Digieva |
Using living yeast to convert sugar to alcohol is a key part of making beer, but it can be time consuming, and the yeast can spoil and ruin a whole batch of the drink. Martin Pumera at the Brno University of Technology in the Czech Republic and his colleagues thought that both issues could be addressed by swapping yeast for tiny, metallic yeast-filled bots.
They made the robots, called BioBots, by encasing yeast cells and nanoparticles of iron oxide in tiny shells of alginate, a gelatine-like material derived from algae. The researchers knew encasing yeast would prevent it from spoiling, but adding iron oxide also made the BioBots magnetic and more chemically reactive. In the lab, they tested these properties by adding the robots to a container of a sugary liquid mixture derived from barley that beer is made from.
Usually, yeast cells float in the mixture, consume the sugars and produce alcohol and carbon monoxide, which gets trapped in the liquid as bubbles. Because the BioBots were made from a soft and porous material, the yeast inside them performed this process as normal, interacting with the liquid the robots were immersed in. But they also offered an advantage: some bubbles released in the fermentation got stuck in the alginate, causing the BioBots to move up and down in the container. This motion sped up the fermentation process, taking between six and 12 hours instead of the more typical three days.
Once the yeast consumed all the sugars in the mixture, fermentation stopped and the BioBots stopped moving. At this point brewers usually must filter the beer to remove any inactive yeast, but for iron-filled BioBots it was quick and easy to retrieve them by exposing the container to a magnetic field, says Roberto Maria-Hormigos, also at the Brno University of Technology and part of the team. Magnetic forces pulled all the BioBots to the surface and the researchers skimmed them off.
Eliminating the filtration step is a time-saving feature of BioBots, but preparing the robots and ensuring they are perfectly clean before use can take a long time, says Pumera. That is why he says BioBots may be better suited for speciality beers that are produced in small batches rather than industrial facilities, which churn out billions of litres every year.
Charles Bamforth at the University of California, Davis, says that though iron oxide’s magnetic and chemical properties may be useful for getting the BioBots to move inside the container, they carry the risk of affecting the beer’s flavour. “Brewers are experts in matters of yeast handling and they are fastidious in avoiding the merest trace of iron in beer as it leads to metallic flavours and the oxidation of beer that causes staling,” he says.
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