Researchers from Yokohama National University created a technique that turns hop waste from beer production into cellulose nanofibers (CNFs).

Due to a rising trend in craft beers, hop production hit a record high in 2019. But, only the flower is used in beer making. The stems and leaves make up 75% of the biomass produced in hop production and typically these materials will end up in landfills.Cellulose nanofibers were produced from waste hop stems by TEMPO-mediated oxidation. Source: Yokohama National UniversityCellulose nanofibers were produced from waste hop stems by TEMPO-mediated oxidation. Source: Yokohama National University

The new technique would reduce beer industry waste, lower the land footprint of beer production and cut back on petroleum feedstocks. The approach upcycles waste products by using hop stems as a raw material to extract CNFs.

CNFs are low weight with high strength and could help reduce the use of petroleum-based plastics in industrial applications. In the past, CNFs have been successfully extracted from wood and agro-industrial wastes. This is the first time that extracting CNFs from hops has been attempted.

Plant cell walls are made of cellulose microfibrils in a matrix of lignin and hemicellulose. The chemical compositions of cellulose, hemicellulose and lignin vary depending on the fiber source.

CNFs have previously been extracted from wood pulp through purification and refined with a chemical or enzyme treatment. These techniques applied 2,2,6,6-tetramethyl/piperidine-1-oxyl radical (TEMPO) to pre-treated wood cellulose, after which the material is gently disintegrated in water to create CNFs that are 3 nm to 4 nm in width.

Building on the TEMPO technique, the researchers reduced the pretreatment process for remaining lignin and hemicellulose in hop stems to obtain CNFs with a median 2 nm width. Chemical composition analysis revealed that hop stems had a proportion of cellulose almost equal to the proportion of wood base cellulose. The team’s technique could replace petroleum plastic and hop waste could be used as an alternative source for CNFs.

A paper on the new technique was published in ACS Agricultural Science and Tech.