Introduction

Myself and others have discussed this a few times in recent past, especially in light of the 40 million lb overage of hops; the idea of using older crop years.  

Packaging and storage technology increasingly becoming more effective so the idea of using older hops should not be as scary as a concept as some make it out to be. Additionally, using older crop year is something from a sustainability point of view that should be top of mind for any brewer, especially those who are long in certain hops.

 As I mentioned before, Dr. Thomas Shellhammer and his team are working on a research study identifying a new metric that will examine and quantify the degradation of aroma, allowing brewers to select older lots more confidently- an “HSI for Aroma” if you will.  

In this article, I’ll be examining two newer studies released in the last year, reviewing the degradation of hops during storage, as measured by the Hop Storage Index (HSI) and how it can significantly influence the sensory attributes of beer. Two studies—Rutnik et al. (2023) and Xu et al. (2023)—provide insights into how aged hops affect the bitterness and aroma profiles during brewing, particularly focusing on kettle-hopping techniques in the first article, and the production of IPAs at various hopping stages. I review them, but I will point out some key draw backs from their findings.

Detailed Analysis of Aged Hops in Brewing

Rutnik et al. (2023): Kettle-Hopping Dynamics with Aged Hops

This study systematically evaluated the chemical and sensory impacts of kettle-hopping with three hop varieties (Aurora, Celeia, and Styrian Wolf) across a spectrum of HSI values. Key findings include:

• Bittering Efficiency: Older hops maintained their bittering potential when added early in the boil, facilitated by the sufficient isomerization time for alpha-acids.

• Aroma Contribution: Late additions of aged hops were less effective, with a noticeable decline in the intensity and quality of hop-derived aromas. This decrement becomes more pronounced as HSI values exceed 0.5 for Aurora and Celeia and 0.6 for Styrian Wolf. 

Xu et al. (2023): Implications of Hop Aging on IPAs

Focusing on Simcoe and Saaz hops, this study explored how aging under different conditions affects IPA flavor profiles:

• Softening of Beer Profile: Moderate aging of Saaz hops, which are high in humulene, resulted in a softer beer character, potentially enhancing overall drinkability.

• Loss of Aroma Compounds: Conversely, Simcoe hops, celebrated for their vibrant aromatic profile, exhibited significant losses in essential oils post-aging, adversely affecting the expected IPA aroma.

Implications for Brewers

From these findings, several practical recommendations emerge for brewers:

1. Utilization of Aged Hops: While aged hops can be effectively employed for bittering (particularly in early boil additions), their diminished aromatic capabilities in these studies* warrant fresher selections for late additions or styles where aroma is a critical feature.

2. Varietal Considerations: Different hop varieties exhibit variable resilience to aging effects. For instance, Styrian Wolf shows a higher threshold for maintaining both bitterness and aroma quality post-aging compared to other varieties.

3. Boil Duration Adjustments: Prolonging the boil can partially offset the negative effects of aged hops on bitterness but is less effective in preserving aromatic qualities (as expected). This adjustment can be strategic, depending on the desired beer profile and the age and condition of available hops.

4. Advanced Products: products such as Terpenes can be produced from older hops, which do allow for older aroma varieties to be used more effectively/sustainably on cold side additions.

*One last point which I think is crucial to mention: while these studies identified the aroma hop (Simcoe) as being adversely affected by aging in an IPA, they do not identify lot selection as being a factor involved. As we have seen from research coming from Virgil Gamache on Amarillo, certain lots and “vintages” of hops can stand up to even newer crop years from a desirable aroma point of view.

Conclusion

The nuanced understanding of how aged hops influence beer quality can guide brewers in making informed decisions about hop selection and usage, but ultimately there is much more research that needs to be done. By optimizing hop freshness and boiling strategies based on the specific hop variety and desired beer characteristics, brewers can better manage the sensory outcomes of their brews. Think about buying and/or utilizing older crop year; you may be surprised!

References

1. Rutnik, K., Ocvirk, M., & Košir, I. J. (2023). The Impact of Hop Freshness on Kettle-Hopped Beers. Foods, 12(23), 4353. https://doi.org/10.3390/foods12234353

2. Xu, H., Sun, S., Wang, X., Zhang, H., & Nie, C. (2023). Aging of Hops and Their Effects on India Pale Ale Flavor. BIO Web of Conferences, 59, 01016. https://doi.org/10.1051/bioconf/20235901016