Abstract
New ways of managing hop sediments from brewing and fermentation of beer are constantly being sought and the existing ones improved as part of the circular economy. These wastes are not generated in large amounts, but the absence of their proper characteristics may lead to further processing errors. The study analyses the composting of hop waste under laboratory conditions and the effects of the biological activity of composts introduced into the soil. The study was carried out on two-hop sediments from two different technological stages of beer production: hot trub (HT) and spent hops (SH). Chemical, microbiological and biochemical analyses, as well as the assessment of phytotoxicity to Lepidium sativum L., were performed in the materials. The results proved that, due to their formation technology, the tested feedstocks are safe from an epidemiological point of view and are not a source of microbial contamination. Inhibitory properties for plant development were found for HT and it most likely results from the organic compound content. The mineral composition of hot trub does not exclude composting if its share in biomass is low. Spent hops (SH) were characterised by a significant total nitrogen content, which affected the composting process. Composting this sediment required the selection of substrates with a wide C:N ratio. The number of microorganisms inhabiting the analysed material was very diverse and varied depending on the type of sediments. The sample that contained the composted SH from dry hopping had a much larger number of microorganisms than the sample with HT from wet hopping.
Highlights
Apart from spent grains, beer production generates two types of solid waste associated with the hopsHop is a specific plant that is introduced into the process to achieve the specific flavour and preservative values
The microbiological analysis of composted hop sediments made in this study allowed to demonstrate a large variety of microorganisms inhabiting the tested feedstocks, while at the same time, lacking potentially pathogenic microorganisms
The study revealed that the number of microorganisms analysed in the soil after incubation with compost based on spent hops (SH) from dry hopping was significantly higher than that determined in soil with compost containing hot trub (HT) from wet hopping
Summary
Apart from spent grains (brewers’ grains), beer production generates two types of solid waste associated with the hops. Hop is a specific plant that is introduced into the process to achieve the specific flavour and preservative values. A very strong, specific aroma and a rather bitter taste are achieved thanks to lupulin obtained from common hop cones. These substances show selective and weak bactericidal and bacteriostatic activity against Gram-positive and Gram-negative bacteria [10,11,12]. The methods of hop application in the brewing process, based on granules or extracts, affect the amount of filtration sediments and their characteristics
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