First Steps Toward Understanding the Regional Identity of Hops Grown in the Willamette Valley, Oregon

Regional identity, or terroir, is the concept whereby the unique flavor and quality characteristics of different crops or products relate to their place of origin, and it is well-studied in winemaking. This study presents preliminary evidence of regional differences in two hop cultivars, Centennial (two locations) and Sterling (three locations), that were managed similarly in the Willamette Valley during 2018 via a collaborative effort among Oregon State University (OSU) (Corvallis campus and Marion County Extension), the Indie Hops-OSU Aroma Hop Breeding Program, Coleman Agriculture, and Red Hill Soils. Soil chemistry and morphology, local weather data during the growing season, and regional climate data were gathered to quantify differences among the sites. The hops harvested from each site were examined via ASBC standard methods for hop acids, total oil, and oil composition. The same hops were used in brewing trials, and the resulting beers were subjected to sensory analysis by a panel of professional brewers and hop growers as well as a panel of trained sensory assessors. Differences were observed in soil and local weather characteristics, plus chemistry and sensory qualities of both the hops and the resultant beers. These results point to the potentially important effects of soil and weather on hop characteristics and open the door to a broader discussion and further inquiry of the regional distinctiveness of hops. The Concepts of Regional Identity and/or Terroir as They Apply to Hops Key to regional identity is the concept that unique flavor and quality characteristics of different crops or products relate to their place of origin. These unique characteristics may result from differences in climate, geology, soil, local management practices, or processing practices. In this regard, regional identity is very similar to, and perhaps is synonymous with, the concept of terroir. The wine industry has a long history of utilizing the terroir concept to help characterize and classify different wines, to identify current and future production regions, and for product marketing. The creation of American Viticultural Areas was based in large part on the premise that regional differences in wine grapes exist, and these differences are perceivable by winemakers and consumers. Beyond wine, other examples of regional identity can be found in a wide variety of food products such as cheese, fruit, coffee, and olive oil (3,22). Indeed, consumers, producers, and buyers have long held preferences for products coming from certain regions. This has grown as consumers in developed countries increasingly have access to products from around the world and are eager to explore, understand, and develop their tastes for products coming from specific regions. In this same vein, brewers and hop producers are interested in knowing how different production regions and practices influence hop cone chemistry and aroma profiles. In the production of beer, hops not only provide bittering and preservative qualities to beer but also flavoring and aroma components. The production and use of aroma hops have risen steadily, driven by craft brewing demand (8). This increase in aroma hop use has potentially opened up new opportunities for regional differentiation and identity. The overarching question is, can hop quality such as chemical profile, flavor properties, and aroma properties be related to specific sites, and if so, what site properties are important? Although evidence linking hop aroma chemistry to production regions is limited, three recent studies conducted on a global scale have begun to address this question (2,16,20). The exact variables measured to delineate a region or define terroir are not standardized; however, they generally include measures of climate, geology, geomorphology, and soil type (5,21,22). The set of variables should reflect attributes known to influence the final product (for instance, timing of fruit maturation, ratio of acid to sugar, and concentrations of specific aroma or flavor compounds). For many products, we do not know the precise variables or the interactions among them that influence the end product. A suite of variables considered important for defining wine grape terroir can provide us with a E-mail: tom.shellhammer@oregonstate.edu https://doi.org/10.1094/TQ-56-4-1215-01 © 2019 Master Brewers Association of the Americas 142 MBAA TQ vol. 56, no. 4 • 2019 Regional Identity of Hops starting point, but one should remember that hops are a very different crop, so the same variables may not be as useful for defining hop terroir. Aroma hop production targeting the craft beer industry is still a relatively new endeavor, and little data exist describing best management practices for influencing hop aroma (besides cultivar choice). However, to begin thinking about the most influential variables of hop quality, we looked at the most studied production aspects—irrigation, growing season temperature, and harvest timing—and also looked at additional variables that are used to describe wine terroir. On a global scale, we also know that latitude plays a strong role in hop development because the initiation of flowering is day length sensitive, and most hop cultivars need sufficient chilling during dormant months for optimal regrowth. For these reasons, hop production has historically occurred between 30 and 52 latitude N or S (7,14). Some studies have shown no effect of irrigation on -acid and -acid contents (6,13). However, Srečec et al. (19) did find a negative correlation between evapotranspiration (an indicator of water and/or heat stress) and hop cone yield and -acid content. In general, it is difficult to decouple heat and moisture stress in these studies. Air temperature can affect bine maturation. High air temperatures during cone development, particularly during the third to fourth week of flowering, might be most critical. Srečec et al. (18) found that the onset of bloom and the time between secondary branching and flowering affected both yield and -acid content. They found that increased heat units negatively affected cone yield and accumulation of -acid. In a drought year, yield was halved from 1,800 to 900 kg/ha, and -acids decreased from 11.5 to 6.2%. Similar patterns were observed over a 6-year period in other work (19). The authors emphasize that temperature, heat units, and rainfall are most critical during cone development (July to August in the United States). Three recent studies show that hop essential oils are sensitive to harvest timing (10,11,17). In each study, hop oil content increased with a delay in harvest. Lafontaine et al. (10) noted that this increase in oil content was associated with increased aroma intensity and citrus quality in Cascade hops. Their analysis of sensory attributes also showed that samples from a given year tended to clump together, suggesting that unique aroma chemistry developed in a given year. Hop acid content may be less sensitive to harvest timing than essential oil content (12,17). Aside from the variables used to define terroir, the scale at which terroir is defined can vary. To date, studies on hop cone chemistry have all been conducted across large geographical domains: for example, comparing hops produced in different U.S. states and in different parts of the world (Europe, Australia, and the United States most frequently) (2,16,20). For instance, comparing Cascade hops from the United States, Germany, Italy, and Slovenia, Rodolfi et al. (16) observed differences in bitter acids and xanthohumol content and distinct aroma profiles among samples; however, no relationships among rainfall, temperature, or latitude were observed. A study by Barry et al. (2) compared Cascade, Mt. Hood, Golding, and Nugget cultivar hops from Germany, the United States, and Nova Scotia and found differences in aroma attributes of both whole-leaf hopped and dry-hopped lagers among panelists. Yet, this study did not examine climate, soil, or any other variables related to terroir among the sites. Similarly, Van Holle et al. (20), evaluated Amarillo hops grown in Idaho and Washington (U.S.A.) and found distinct differences between the production regions and between years at the same location. The size of the geographical domain likely impacts the relative importance of different variables that might affect regional differences. When examining differences at the farm or field level, for example, climate factors become less important relative to soil properties and drainage. There is growing evidence that regional differences in hop chemistry and consumer-detectable aroma hop characteristics may exist, at least at the national and global levels. However, we cannot yet tease out specific climate effects among regions or years if they exist, nor do we understand the impact soil variation and management practices might have. Studying these factors at the farm level may provide insight into the effect that these variables might have and guide management decisions for high-quality aroma hop production. The study described herein examined two American hop varieties, Sterling and Centennial, grown at three different locations within the Willamette Valley. The work began at the request of Coleman Agriculture, Oregon’s largest hop producer and one with over 120 years of continual hop growing experience. Aware of consumer interest in regional identity, its use in the wine industry, and growing interest among hop buyers and brewers, Coleman Agriculture wanted to better understand their own farm sites and gain insight into what variables might affect hop quality at the farm level. They wanted to characterize the soil variability among farm locations and within a field to help guide management decisions. This work has begun a longer journey toward understanding and characterizing regional differences of hops grown in the Willamette Valley, Oregon. Methodological Approach to Assessing Regiona