| Project Name: | Characterisation and assessment of hop processing by-products |
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| BPA Number: | 2122 |
| Funding Round: | |
| Report(s): | Characterisation and assessment of hop processing by-products |
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Summary of Project and Key Findings:
This study aimed to characterise the by-products or “waste” steams from the hop plant picking process used to recover cones for use in the brewing industry. The New Zealand (NZ) hop industry, concentrated in the Tasman Region, produces ~1400 metric tonnes of dried hop cones per annum and production is set to expand in the near future. As the cone makes up less than half of the hop plant mass, large amounts of hop by-products are produced and directed towards low-value uses.
This report provides the foundational information needed to:
- estimate by-product yields
- determine by-product composition
- evaluate applications for better ways to utilise the by-products.
The trial work was completed at The New Zealand Institute for Plant and Food Research Limited (PFR) Motueka site, which hosts the PFR hop breeding programme, production orchards, and hop processing and evaluation facilities. Seven cultivars were selected from the PFR orchard for production yield and crude compositional assessment. Two were selected for further in-depth assessment, including targeted and untargeted chemical analysis across three PFR chemistry teams. Cone and by-product samples were prepared for analysis in up to three methods, oven dried (as per industry practice for cone drying), freeze dried and fresh frozen.
Across the seven cultivars, the yield of cones produced was 24.8%, leaf by-product 36.8%, petal by-product 2.9% and bine by-product 33.7%, on a dry matter (DM) basis. Therefore, three quarters of the hop plant mass was by-product.
Petals had notable hop compounds present, including terpenes, bitter acids and prenylated flavonoids at rates of about 25 to 33% of that found in the cone, and present an opportunity for utilisation.
Subsets of hand-picked leaves were collected from the leaf by-product. The flavonol and flavan-3-ol polyphenol content in leaves was the highest across the hop parts. However, these were found to contain low concentrations (mg/kg DM) of total bitter acids prenylated flavonoid (PF) concentrations (mg/kg DM). This makes bitter acid or prenylated flavonoid recovery from leaves a difficult practical and economic proposition.
Bines, the main stalk of the hop plant, had the highest levels of neutral detergent fibre (NDF) and lowest levels of crude protein (CP), crude fat (CFat) and metabolisable energy (ME). The content of bitter acids and prenylated flavonoids was very low and reflects the lower amount of residual cones present in this by-product.
The fibre properties of the bine were reviewed in depth by AgResearch. This analysis revealed that although fibres could be extracted by hand methods, it would likely be difficult to scale to commercial levels, from both practical and economic perspectives.
Leaf by-product had crude compositions comparable to forage and had the highest ME value of the by-products, making it a suitable candidate for further research for use as an animal feed.
Conclusions
The key findings from the study were:
- The yield of cones produced was 24.8%, leaf by-product 36.8%, petal by-product 2.9% and bine by-product 33.7% on a dry matter basis. Therefore, by-products made up over three-quarters of hop plant.
- Petals had notable hop compounds present, including terpenes, bitter acids and PF. The different ratios of terpenes and terpenoids in the petal compared to the cone may mean they provide a different aroma opportunity from a brewing perspective.
- Leaf and bine by-product have potential as animal feed as crude compositions were comparable to typical forages and a literature review of their suitability was favourable.
- Applications such as textile and construction fibre from bine-by-product and biofuels from leaf and bine by-product do not seem feasible at this stage
- Leaves had notable levels of flavonols and flavan-3-ols but little in the way of bitter acids, PFs, terpenes or terpenoids. Overall, leaves do not present a feasible material for extraction.
- There were unidentified compounds of notable magnitude found in the hop cones. These look to contain prenyl groups. If these are novel compounds, they might have applications as bioactives.
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