Self-propelled “BioBots” bob up and down as they ferment sugars to produce beer. Credit: Adapted from ACS Nano 2023, DOI: 10.1021/acsnano.2c12677
Beer brewing is a lengthy chemical process in which yeast is used to ferment sugars from grains into alcohol, flavor compounds, and carbon dioxide gas. This process can take up to four weeks, during which the beer can be at risk of spoilage; additionally, further steps are needed to filter the yeast from the beer. Researchers from the Brno University of Technology and University of Chemistry and Technology Prague have developed a new method to speed up the beer brewing process, using tiny, self-propelled, yeast-containing “BioBots” that can be easily removed from the final product with magnets.
Previous research has suggested that encapsulating yeast in polymer capsules can help prevent spoilage and speed up the brewing process. The researchers built on this concept by mixing active yeast, magnetic iron oxide nanoparticles and the biocompatible polymer sodium alginate and adding drops of the mixture into a ferric chloride solution. Upon contact with ions in the ferric chloride, the sodium alginate solidifies, trapping both the yeast and iron oxide particles within. Pores were formed in one half of the particles using a pH gradient within an electrochemical cell – the half exposed to the alkaline side became porous while the other half remained intact. The 2-mm-wide capsules, referred to as BioBots, were added to malted barley wort to test their ability to facilitate fermentation.
The researchers found that the yeast inside the BioBots remained active and were able to ferment sugar in the wort, producing carbon dioxide bubbles in the process. The bubbles would cause them to be propelled upward, release carbon dioxide into the air at the surface, and then sink back into the liquid, producing an autonomous bobbing motion. The half-porous structure of the particles, known as a “Janus” structure, was found to enable this oscillation, as non-Janus particles trapped carbon dioxide and remained floating in the solution as a result. The self-propelled BioBots were able to ferment the sugar in the wort faster when compared with free yeast cells. Once all of the sugar was fermented, the capsules sank to the bottom of the container, where they could be easily separated using a magnet due to the iron oxide component. Additionally, the particles could be reused for up to three more fermentation cycles. This research was published in ACS Nano.
The BioBot technology could greatly speed up the brewing process, both by catalyzing fermentation and removing the need for a filtration step. Additionally, the hybrid magnetic, biopolymer particles could help reduce waste from spoilage and conserve resources due to their ability to be reused. The authors noted the electrochemical cell used to produce the Janus structure could be 3D printed, making BioBot production scalable for potential industrial applications.