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Hop Plant Health Impacts Harvest Timing and Aroma

hop cones drying
Cascade cones dry in the CLS Farms kiln during harvest.

For years, the CLS Farms team has explored the topic of hop-picking windows and their impacts on aroma and flavors. While we looked at inherent intra-varietal differences, we’re now looking into other factors that impact harvest dates, and more importantly, aromas. 

At this year’s Craft Brewers Conference, our presentation analyzed two distinct lots of Cascade harvested almost exactly one month apart at CLS Farms. One lot came from a virus-infected field. The other came from a second-year planting of a virus-free field. 

Virus-Infected Field Harvest Date: 09/06/2023

Virus-Free Field Harvest Date: 10/05/2023

Cascade is traditionally picked in early September with aromas of grapefruit and pine with background floral and other citrus notes. But despite a wildly famous and versatile variety, it’s experienced an unreliable last few years. 

Hop varieties, similar to humans, catch viruses. Some varieties experience them worse than others, but Cascade is especially susceptible to viruses and viroids such as Hop Stunt Viroid, causing significant decreases in yield and overall plant health. Discerning a virus-infected field versus a non-infected field is easily apparent as the bines look thin and well, stunted.

As climate change and other input costs rise that impact grower production, it’s increasingly important to have agronomically stronger plants and varieties. In the last few years, a significant amount of Cascade hop acreage has been replaced with clean, virus-free rootstock to enhance overall yields. Higher yields usually equal fewer inputs per pound of hops produced.

However, we’ve discovered that planting virus-free rootstock or pots significantly impacts hop aroma and harvest timing. For years, we’ve understood anecdotally that impact, specifically on Cascade, as varying aromas and yields have made it difficult to achieve consistent hop quality. 

To further look into this issue, we implemented the HopTechnic Harvest Readiness program in 2023 alongside our normal in-field sensory program to better understand what occurred daily in the Cascade virus and virus-free fields on our farm.

As we approached early September, our “normal” Cascade field exhibited aromas that we’d normally expect coinciding with typical terpene and polyfunctional thiol compositions.

But the divergence became apparent as the Cascade cones in our “late” field still maintained a pearl green appearance and slightly underripe aroma once we entered the third week of September. On October 5th, we finally moved the top cutter and crew over to the virus-free field to harvest it. 

No matter the variety, any hop harvested past its prime will likely give you a cheesy, onion or garlic aroma that’s undesirable by many brewers. Throughout harvest, we shared this interesting case with those coming through the farm. Many feared for the overripeness that was expected once we harvested it.

But when we finally dried it down and pulled a sample for our internal team, it presented aromas of tropical fruit and deep citrus with accompanying notes of woodiness and resin. Definitely over the edge, but not enough that it became unpalatable – just enough edge coupled with some fruit not normally associated with Cascade aromas.

It’s important to highlight that if this virus-free field were harvested at the same time as our virus-infected field, it would not have been ready. Despite transitioning more acreage to virus-free plant material, growers continue harvesting Cascade at its usual timing, overlooking the beneficial impact viruses can have on aromas. 

Without proper attention and in-field sensory evaluation, growers risk harvesting virus-free fields prematurely, resulting in overly green aromas that don't meet the needs of most brewers.

For this year’s Craft Brewers Conference in Las Vegas, we worked with the John I. Haas sensory and brewing teams to evaluate the impacts of harvest dates on the finished beer. CLS Farms is a large supplier to John I. Haas, and we have worked closely with the sensory team to deliver hops based on a dynamic picking window versus a fixed picking window.

John I. Haas uses a standard base beer recipe and dry-hopped each beer with the specific lot for evaluation. We also sent both the hop and beer samples to HopTechnic Lab for terpenes and polyfunctional thiol analysis.

When evaluating the polyfunctional thiols in the Cascade hops lots and beers, here is what the lab found:

polyfunctional thiol beer test
John I. Haas brewed test beers dry-hopped with the two Cascade lots — virus vs. virus-free — to determine how flavor was impacted by the plant health and harvest date. All beer samples were further tested by HopTechnic.

Based on these results provided by HopTechnic, there were higher polyfunctional thiol compositions, specifically in 4MMP, in the “normal” (virus-infected) Cascade lot than the “late” (virus-free) Cascade in the beers. 

This data is some of the first, or only, research into how viruses and viroids impact hop aromas, and therefore, your beers. Plant stress is well-studied in other agricultural products like wine grapes, but it’s typically related to heat or drought stress. The effect that specific diseases have on hop plants is just beginning to show their complexity.

Now, we’re not necessarily advocating for only planting virus-infected rootstock. Yield considerations are serious, and the effects of viruses on those fields are significant. But as a brewer, it’s important you’re aware of why your hops might smell different or not fit the profile of what you would expect to smell of a specific variety.

Growers opting to switch acreage over to virus-free rootstock every few years will impact the aromas coming out of the fields unless careful attention to in-field sensory and harvest timing is given. And what we know to be Cascade’s “typical” picking window is likely an effect of virus-infected plants. 

With acreage shifting to virus-free plant material, we have to ask ourselves… 

  • Will this fundamentally change when Cascade is harvested? 

  • How does this impact the overall harvest schedule when Cascade could mature at the same time as other varieties when it previously did not? Does this impact labor costs if harvest timing needs to be extended?

  • What are the aroma considerations? Will this result in widely underripe lots of Cascade going forward? This is especially important for brewers that use Cascade in core beers.

We’re in the early stages of studying this issue and providing evidence-based research to what we’ve noted anecdotally for the last ten years. Currently, there’s no inoculation treatment for hop plants experiencing virus and viroid symptoms. Growers rely on adjusted training dates, nitrogen applications, and most simply, decreasing their margin of error in general farming techniques to mitigate those issues.

For a look at the presentation from the Craft Brewers Conference where we dove into all the breakdowns on sensory and chemical composition of both lots, head to our Hop Picking Windows page to download the PDF.

Do you have questions or comments? Shoot Claire an email at


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