The IPA train keeps a-rollin’ for brewers – as does consumers’ desire for unique flavors and locally sourced ingredients, including hops. However, the more sustainably-minded sippers and brewmasters might be chagrined to learn that nearly three-quarters of the hops plants used in beer making end up unused. There’s good news, though. Science has come through with another win. A group of Japanese researchers has developed a technique that “upcycles” the waste hop biomass into cellulose nanofibers (CNFs).
Global hops production hit a record high in 2019. In addition to adding rich bitterness and floral or citrus aromas and flavors, hops are traditional preservatives in beer. As the craft beer industry continues to grow, so the does the demand for hop flowers (or cones). But the flowers are the only parts of the plant used in making beer. The stems and leaves, which are about 75% of the biomass produced in hop cultivation, are typically burned or sent to the landfill. Turning the waste into CNFs should help reduce the industry’s growing waste and land footprint.
A group of researchers at Yokohama National University developed a technique that uses hop stems as raw material to extract CNFs. There has been increasing interest in CNFs since the 2000s due to their outstanding properties, including low weight, high strength and stabilization. CNFs are expected to be used as excellent plant-derived materials to reduce the amount of petroleum-based plastics in various industrial applications, like in the automotive and housing industries as well as food and cosmetic fields.
“This really would deserve a hearty ‘cheers’ if we managed to reduce dependence on petroleum while also radically reducing the agricultural waste from the beer industry,” said Izuru Kawamura, associate professor in the Graduate School of Engineering Science at the university and the lead researcher on the project.
CNFs had been extracted successfully from wood and from agro-industrial wastes, “but until now, no attempt had been made to isolate CNFs from hop stems,” Kawamura added.
So how does this work? Plant cell walls are made of cellulose microfibrils (tiny, slender fibers) in a matrix composed of lignin and hemicellulose. Generally, CNFs are extracted from wood pulp through a series of purification steps followed by refinement via treatment with chemicals or enzymes. A previously used technique involving the application of something dubbed TEMPO to pretreated cellulose from wood followed by a gentle mechanical disintegration in water resulted in CNFs three to four nanometers in width. Kawamura’s team used the TEMPO technique but reduced the pretreatment processes for removing lignin and hemicellulose in hop stems prior to the TEMPO step. Even without the pretreatments, they obtained CNFs with a median of about two nanometers. The researchers discovered the hop stems contained a proportion of cellulose that is almost the same as that of wood.
Big picture: This means that not only could this technique replace petroleum, but that hop waste could also be used instead of wood as an alternative source for CNFs.
To follow up, the scientists want to prepare some emulsions stabilized by hop stem-derived CNFs and demonstrate their feasibility. If they’re successful, it should lead to a significant reduction in the amount of conventional synthetic surfactants used. More beer, less waste, fewer plastics and fewer trees cut down for cellulose. We can raise a glass to that.