Summary

1. Reusing dry hops in brewing is a complex subject, with potential impacts on flavor and extraction efficiency. Studies have found that up to one-third of the hop compounds can be lost during the initial use, raising questions about the effectiveness of reusing them.

2. The research, including an analysis of Hauser's study on dry-hopping extraction efficiency, provides mixed conclusions on reusing dry hops, with factors like hop creep adding complexity to the decision.

3. Overall, the evidence suggests that while reusing dry hops may be possible, the challenges and potential loss in quality should be carefully considered before implementing this practice.

Dry hopping has cemented its place as an irreplaceable technique for beer enthusiasts and brewers alike. Popularized primarily by the surge in demand for hop-forward beers like the India Pale Ale (IPA), but dating back centuries, dry hopping involves introducing hops to the brew post-boiling during the cold side of fermentation, which infuses the beer with intricate aromas and flavors without significantly altering its bitterness (Stokholm, 2020).

However, one key aspect that’s raising eyebrows and questions among brewers is the potential to reuse dry hops. With sustainability and efficiency becoming more paramount in modern brewing, the prospect of re-using spent dry hops is an intriguing avenue to explore.

Historical Context and Modern Revolutions

Dry hopping has roots tracing back centuries, but its modern interpretation and application have been fundamentally transformed by American brewers. Historical notes from Paul Farnsworth suggest that early breweries like Truman, Hanbury & Buxton in Burton-upon-Trent used a modest six ounces of Goldings per U.S. barrel for individual casks. In contrast, today’s brewers might use up to 15 times that quantity, underscoring the revolution in hop utilization (Hieronymus, 2020).

This shift brings to light an essential concern: the sustainability of discarding such large quantities of used hops. What potential aromas and flavors might still be lurking within them?

Unraveling the Potential: Extraction Efficiency by Hauser

While it's tempting to believe that once-used hops have given their all, Dean Hauser's study at Oregon State University titled "Extraction Efficiency of Dry-Hopping" suggests otherwise. This research, conducted by Dean G. Hauser, Scott R. Lafontaine, and Thomas H. Shellhammer explored the efficiency of dry-hopping and the potential value of spent dry hops, emphasizing the retention of valuable volatile and non-volatile hop components after dry hopping.

In their pilot-scale study, an unhopped pale ale was statically dry-hopped with varying lots of whole cone Amarillo®, Centennial, and Cascade hops. The findings were striking: regardless of the hop variety, approximately one-third of the dry-matter composition of the hops was lost during dry hopping. However, there was a high retention of both α-acids (77% on the pilot scale) and essential oils (51% on the pilot scale).

Spent hop material from an industrial-scale brewery also revealed significant retention values: 52% for α-acids and 33% for essential oils. Notably, the oil remaining in these spent hops was enriched in hydrocarbon compounds but had reduced oxygenated compounds. 

Furthermore, Hauser’s research also delved into the nuances of dry-hop extraction efficiency. The study found that the extraction of essential oils and α-acids is not a straightforward linear process. Various factors, including temperature, contact time, and hop pellet size, significantly influence the extraction efficiency (Hauser et al., 2019). Therefore, when considering the reuse of hops, understanding these variables becomes paramount. 

Sensory Exploration and the Taste Frontier

While sustainability and efficiency are significant drivers, the world of brewing is, first and foremost, about the sensory experience. Oregon State University extended their research to evaluate the sensory implications of beers brewed using reused dry hops. Interestingly, beers bittered with these hops showcased heightened bitterness and retained comparable aroma profiles, challenging the preconceived notion of spent hop inefficacy (Hieronymus, 2020).

Furthering the sensory examination, Salamon et al. (2022) focused on β-myrcene, a prominent volatile component in hops. Through modified dry hopping, they achieved richer concentrations of β-myrcene, suggesting that nuances in the dry hopping approach can drastically influence the beer's final aroma and taste.

Hop Creep: The Unintended Consequence

A pivotal challenge facing the reuse of dry hops is hop creep. Caused by residual enzymes in hops that can convert unfermented dextrins in beer into fermentable sugars, hop creep can lead to unplanned fermentation, potentially causing over-carbonation and flavor alterations (Hieronymus, 2020).

When reusing hops, brewers might inadvertently amplify the hop creep effect since the initial brewing process might not deplete the hops' enzymatic potential. Thus, reintroducing them can lead to a higher concentration of these enzymes, requiring brewers to account for this phenomenon and adopt preventive strategies.

The Road Ahead: Sustainability Meets Innovation

The ecological and economic implications of reusing spent dry hops are vast, promising reduced cultivation areas, waste reduction, and minimized resource utilization. Still, this potential revolution isn't devoid of challenges.

Brewers like Josh Chapman at Black Narrows Brewing recognized this potential and aimed to harness what was previously discarded (Hieronymus, 2020). Similarly, Bosque Brewing in New Mexico has termed this reuse as “second-generation dry hopping.” At Pennsylvania’s Forest & Main, spent dry hops have been reused to create unique saison flavors (Hieronymus, 2020). This re-utilization, from an environmental perspective, also resonates with the sustainability ethos. Reusing spent hops not only reduces waste but could also save costs and diminish the need for extensive hop farming, thereby mitigating the environmental footprint (Hieronymus, 2020).

Questions abound concerning the optimal storage of reused hops, the preservation of their aromatic compounds, and understanding the balance between the loss and retention of critical compounds after the first brewing cycle. The insights from Hauser’s study on extraction efficiency provide a roadmap, suggesting that a nuanced understanding of the extraction process can guide brewers in maximizing the potential of reused hops (Hauser et al., 2019).

Conclusion 

Future research must continue to probe into the ideal conditions and methods for reusing dry hops, while recognizing the delicate balance between economic efficiency and the preservation of taste and quality. Collaborative efforts between brewers, researchers, and industry experts will be essential in advancing this practice and achieving a brewing process that is both flavorful and environmentally responsible. The potential rewards for the industry, both in terms of innovation and sustainability, are considerable, making the pursuit of this knowledge not only worthwhile but essential for the future of brewing.

References:

1. Lafontaine, S. R., & Shellhammer, T. H. (2019). Investigating the Factors Impacting Aroma, Flavor, and Stability in Dry-Hopped Beers. MBAA TQ, 56(1), 13–23.

2. Hieronymus, S. (2020, April 24). Elements of Beer: Recycling Hops in the Brewhouse. Craft Beer and Brewing Magazine. Retrieved from https://beerandbrewing.com/elements-of-beer-recycling-hops-in-the-brewhouse/

3. Salamon, R. V., Dabija, A., Ferencz, Á., Tankó, G., Ciocan, M. E., & Codină, G. G. (2022). The Effect of Dry Hopping Efficiency on β-Myrcene Dissolution into Beer. Plants, 11(8), 1043. https://doi.org/10.3390/plants11081043

4. Stokholm, A. (2020). Dry-Hop Induced Refermentation: An Overview and an Investigation of Agronomic Influences on Hop Diastatic Potential. Oregon State University.

5. Hauser, D. G., Lafontaine, S. R., & Shellhammer, T. H. (2019). Extraction Efficiency of Dry-Hopping. Pages 188-198. Received 13 Feb 2019, Accepted 07 May 2019, Published online: 18 Jun 2019. https://doi.org/10.1080/03610470.2019.1617622