Your Spent Hops and Grains, a Valuable Resource For Our Food Chain?

Brewing by-products can supplement existing foodstuffs

Dear brew enthusiasts

In this weeks episode of the beerologist, we will talk about malted grains again. But rather than describing work on post-harvest diseases and their impact on malt quality, we will talk about the value of spent grains and hops!

Brewers will be keenly aware that the brewing process can produce significant waste streams. Spent grains, hops and yeast represent the major solid waste products that must leave the brewery at some stage. Currently, waste disposal is not without costs and, in the best-case scenario, come with little profit, if any at all.

In this context, the observation that spent grains and hops could be the source of valuable chemicals and food additives is relevant to the bottom line. Given that a growing (micro) brewery industry produces increasing amounts of solid waste, researchers at the Italian Brewing Research Center CERB (University of Perugia) and the University of Basilicata (Potenza, Italy) formally assessed the solid waste re-use case. 

In their work, the authors assessed the chemical content of brewing spent grains (BSG) and brewing spent hops (BSH) after producing two beer types: a Belgian Strong Ale (BSA) and an Imperial Red Ale (IRA). 

The teams, led by Elisabetta Bravi and Giuseppe Perretti, collected said samples and determined the various parameters that inform on food safety. The authors measured Ash values (indicative of key constituents left over after burning the samples), water activity (aw), a measure of the potential for microbial spoilage, and dry weight. These analyses revealed that all the values measured and indicative of food safety met acceptable levels. In short, the raw products produced at the microbreweries were deemed safe for entry into the food chain.

Figure 1 from Bravi et al (2021). β-glucans and arabinoxylans content of the brewing spent grains, BSG (A), and spent hop, BSH from Imperial Red Ale (IRA) and Belgian Strong Ale (BSA)

Next, the authors measured the amounts of β-glucans and arabinoxylans expressed as a dry matter percentage. Both β-glucans and arabinoxylans considered dietary fibres and are known to improve human health. Their analyses showed that, as expected, spent grain (BSG) had higher levels of both dietary fibres when compared to those found in spent hops (BSH). Grain left over from the Imperial red ale (IRA) was particularly high in arabinoxylans and, to a lesser extent, β-glucans. While both compounds were found in BSA grain samples, levels were significantly lower. 

In addition to dietary fibres, phenolic compounds with antioxidant activity have positive impacts on human health. Given that crop-derived products are rich in phenolic and other antioxidant compounds, they investigated their BSG and BSH samples level. Three independent assays were used:

• Ferric reducing antioxidant power (FRAP) assay

• 2,2-diphenyl-1-picryl-hydrazyl-hydrate free radical method (DPPH)

• Azinobis ethyl benzthiazoline sulfonic acid- based assay (ABTS).

All these assays use different chemistries and readouts to measure levels of antioxidant potential. The authors used these three methods and demonstrated that both spent grains and spent hops contain significant antioxidants levels. Furthermore, these levels depend on the recipe used for brewing each beer type. For example, the BSG and BSH from the Belgian strong ale consistently showed higher antioxidant activity levels compared to the IRA counterpart. 

Figure 2 from Bravi et al (2021). Antioxidant activity, measured in brewing spent grain (BSG), Brewing spent hops (BSH) from Imperial Red Ale (IRA) and Belgian Strong Ale (BSA) through three different methods (FRAP, DPPH & ABTS).

From this work, it is clear that the beer production process yields essential dietary products besides beer! As waste streams continue to flow and demand for dietary foodstuffs remains high, we can expect the emergence of use cases that carry significant benefit to both the brewer and the consumer. How? This is one question that I hope to put to the authors of this work. As always, we will contact them for a flame side chat!

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Cheers,

Edgar, The Beerologist

Edgar Huitema is a Scientist, Brewer & Scientific Consultant at ExtrAnalytics. Subscribe to my free newsletter to get the latest advances in science. Contact me if you wish to discuss your needs and our research.