by Andrew Walsh (Brewing Techniques - Vol. 6, No.2)
Precise methods of hop analysis have made it possible for experts to take a fresh, hard look at the lineage of today’s noble varieties. Their discoveries are rewriting the pedigrees of some of your favorite aroma hops.
Traditional noble hops such as Tettnanger, Hallertauer Mittelfrüh, and Czech Saazer are generally thought to be the aroma hops most highly prized by brewers of “continental” beer styles.* Especially among American craft brewers, they are a delicacy eagerly anticipated in shipments from abroad and often quick to sell out. Their perceived superiority in flavor and aroma have made them the hops against which some brewers measure all other hops.
Although their standing among brewers has never been disputed, “nobility” itself has never been clearly defined outside of traditional associations with geography and variety. Modern methods of analysis now make it possible for researchers to accurately pinpoint hop lineage, and their findings are confounding many of our assumptions about hop varieties. Published results of these tests have shown, for example, the gene pool of today’s nobles to be shallower than supposed.
The most striking example is the case of U.S. Tettnanger. U.S. Tettnanger (the only noble hop variety successfully grown in the United States today) has been commercially available for about 10 years and is currently the fifth largest variety, by quantity, grown in the country. Among aroma hops, it is second only to Willamette in acreage. Its title clearly identifies it as an American-grown clone of the noble hop grown in the Tettnang district of Germany.
Recently published research tells a different story, however. This research shows that U.S. Tettnanger is in fact analytically identical to English Fuggle as well as the similarly misnamed Savinja Golding (also known as Styrian Golding), both of which are of far more working class descent than true German Tettnanger hops (1,2,3,4).* (More on this later, in the section titled, “Hop Research Methods of Varietal Identification.”) The fact that for a decade U.S. Tettnanger has been successfully sold and used as an American-grown noble hop raises serious doubts about the absolute importance of a noble “pedigree” in brewing.
*Noble hops are loosely defined as native continental (not British) European aroma hops and some of the cultivars that arose from them. The hops listed above are the best known, but Hersbucker, Spalter, and Lublin could also be included.
This article reports the results of an investigation into hop nobility. What makes a noble hop “noble”? What is it about the chemical composition of these hops that gives them special character? Is the assumed superiority of noble hops justified in light of ongoing discoveries in hop research?
*The same methods of analysis also show that many other noble hop varieties are indistinguishable from one another and could in fact be regarded as the same variety sold under different designations (see the box on page 63, “Other Cases of Mistaken Identity”).
The Chemistry of Hop Aroma
To grasp the essence of what makes noble hops noble, we must first touch on their composition and chemistry. Noble hops are traditionally low in alpha-acids, the compounds specifically responsible for most bittering, and are thus by definition “aroma hops.” As with all hops, the all-important aroma and flavor of noble hops comes from their essential oils (alpha- and beta-acids are hop resins, which comprise about 10–28% of hop compounds, while flavor is also affected by resins and polyphenols ).
Essential oils are the substances responsible for the fragrances of many flowers and vegetables. They are typically defined as that fraction of oil that can be separated from the parent plant by steam distillation. Hop scientists have shown considerable interest in these oils because of their contributions to the flavor and aroma of beer. The chemistry of essential oils is complex, and to date several hundred compounds have been identified and categorized (6).
The essential oil content in hops typically ranges from only about 0.4% to 2.0% of all hop compounds. These oils, together with the hop acids, are found in the lupulin glands around the base of the bracteoles and — in the case of seeded hops — also on the seed coat of the hop cone. The chemical composition of essential hop oil is conventionally described under three headings: hydrocarbons, oxygenated components, and sulphur-containing components.
Hydrocarbons: The hydrocarbon fraction includes myrcene and the sesquiterpenes humulene, farnesene, caryophyllene, and selinene. Hydrocarbons constitute 70% of the essential oils, and their aromas dominate raw hops. Myrcene alone (which contributes a fruity, pinelike aroma ) can form up to about two-thirds of the total hop oil content. Most hydrocarbons, however, are either lost during the boil or removed in the fermentor by way of CO2 flushing or by adherence to yeast. Myrcene, for example, is quite volatile and oxidizes readily; little survives into beer unless the beer has been dry-hopped. Myrcene levels in stored hops also drop quickly over time.
Hop flavor in beer cannot be attributed to a single compound; rather, it is the result of the additive or synergistic effects of many components. About half of the hop-derived volatile compounds found in beer are not even present in raw hops and are instead formed during the boiling and fermentation processes (8). For example, the sesquiterpene hydrocarbons (mainly humulene) are important because they are thought to be precursors to critical hop oil oxidation products that enhance aroma (8,9,10).
Oxygenated components: The hop oil hydrocarbons gradually oxidize during plant maturity and subsequent storage to form a myriad of oxygenated compounds that significantly affect beer flavor. It is difficult to trace the fate of individual constituents because they degrade by a number of pathways.
Although the hydrocarbons constitute the major portion of the essential oils, the oxygenated components (comprising the remaining 30%) are more important in beer flavor because they are more soluble than the hydrocarbons and less volatile in the copper boil. These compounds therefore remain in the wort and in the beer, where they can chemically interact with other ingredients.
Hop esters. One often-underestimated aspect of beer aroma is the ester fraction, which is probably the most important of all the components (6). These fruity aromas are usually associated with yeast and fermentation, but can also be enhanced by late and dry hopping. Most hop esters are methyl esters that can survive into beer, but some may be converted by yeast enzymes into other forms (by transesterification to ethyl esters, for example).
One striking example was reported by Murakami et al., who found that wort that has been late-hopped with Hallertauer hops produced beer with 14 times the concentration of the ester ethyl hexanoate than that of beer fermented from the same wort but without late-hopping (11). Ethyl hexanoate is described as having an apple/anise seed aroma and is usually regarded more as a yeast ester than as a hop essential oil component — though the study clearly showed a connection. Beer late-hopped with Fuggles and Galena also contained much higher levels of this ester than the control beer.
Sulphur-containing components: Although sulphur-containing compounds in hops generally occur in trace amounts, as a group they are extremely flavor-active and impart undesirable musty, vegetal, and sulphury flavors to beer. Treating hops with sulphur dioxide during drying or dusting hop plants to prevent fungal disease can lead to an increase in these unwanted components (6).
A true noble hop has certain chemical credentials to back up its reputation for excellence. A noble hop generally has low alpha-acids, particularly cohumulone (<25% of the total), and an alpha/beta ratio close to 1:1 (12,13). High cohumulone levels are said to result in poor foam stability, unpleasant bitterness, and poor aroma; therefore, we can infer that because noble hops have low cohumulone levels, they enjoy the converse. The essential oil content is generally low in myrcene and high in humulene. The ideal humulene/caryophyllene ratio for noble hops is greater than 3:1 (12).
Oxidation and noble character: Most researchers believe, however, that the main source of noble character is provided by the oxidation products of the sesquiterpene hydrocarbons, particularly those of humulene (8,9,10) – humulol, humulenol, humulene monoepoxides, humulene diepoxides. Linalool oxides (oxygenated alcohols) have also been implicated (10). These oxidation products are formed during hop kilning, storage, and boiling. Temperatures above 158 °F (70 °C) significantly increase their relative concentrations. The fact that some are produced during wort boiling may explain why some boiling of noble hops (no more than 10–15 minutes) is usually recommended in lager brewing to remove some undesirable compounds without boiling off all of the volatiles.
Nobility ages with grace: Many brewers also prefer noble hops with some age for the same reason. Cheesy-smelling hops should be avoided, however; off-aromas derived from isobutyric and isovaleric acids are the result of oxidation products of the hop resins. Because these compounds are very volatile in steam, their presence is inconsequential in bittering hops but very damaging to aroma hops, particularly those used for dry hopping.
During the 1980s, hop researchers Robert Foster and Gail Nickerson investigated the manner in which hop varieties age and the effect age had on the plants’ “hoppiness” (14). They found that hops could be divided among roughly four categories based on their chemical constituents and on essential oil measurements. The hops in category I (including Wye Challenger and Wye Target) demonstrated good hoppiness whether fresh or aged. The hops in category II (including Cascade and Galena) should be used fresh when used for aroma. Category III hops should have some age. It is interesting to note here that noble hops fall into category III, as do the Fuggle-type hops (Fuggle, Willamette, and Styrian Golding); all of these hops have high humulene content. Category IV hops, including Nugget and Cluster, have a low hoppiness potential under any aging conditions and are not generally considered good aroma hops (Perle is an exception).
Of the three kinds of hoppiness (aroma) defined in the study (floral, citrus, and noble), Fuggle rated highly in noble hoppiness and was remarkably similar to German Tettnanger. This is not sufficient evidence by itself to conclude that Fuggle and Tettnanger are the same hop variety, but it does help us to understand how they could be confused with one another for so long. It would difficult, for example, to imagine the same thing happening with Tettnanger and Cascade!
Hop Research Methods of Varietal Identification
When it comes to identifying an unknown hop, scientists have about half a dozen techniques at their disposal. Methods of analysis have improved greatly in modern times and stand to become even more precise with time.
Physical appearance: Traditionally, growers relied on the appearance of the plant and cone to identify hops. This is what is termed morphological identification. This method can be very imprecise, however, and many of today’s numerous interrelated hop varieties are impossible to distinguish just from their appearance alone.
Acid content: Similarly, analysis of the amount of alpha- and beta-acids produced by the plant provides only a general indication of variety. Considerable variation occurs within a particular variety from year-to-year because of differences in climate, particularly the amount of sunlight (15). Even plants of the same variety grown 10 feet apart can possess different resin contents. Storage deterioration will also greatly affect alpha-acid levels. The alpha/beta ratio, however, is a varietal characteristic, as are the proportions of the alpha- and beta-acid analogues cohumulone and colupulone. Thus, the relative amounts of all of these compounds may decrease proportionally, but the ratios stay roughly the same, even under varying conditions. Consequently, the ratios can serve as useful aids in identification, but are usually still insufficient to identify an unknown sample.
Essential oil analysis: Determination of the individual amounts of the primary essential oil constituents (myrcene, humulene, selinene, farnesene, and caryophyllene) further assists in the identification process, although myrcene levels in particular will vary greatly for a given variety, depending on climate, picking time, kilning, and storage conditions. For example, in the three weeks before maturity, Fuggle has been found to increase in alpha-acids by only 10–15% while in the same period the essential oil content trebled — mostly because of myrcene (16). The ratios of the sesquiterpenes, however, are often used in varietal identification because they have been shown to distinguish varieties and are comparatively independent of growing and storage conditions (1, 15, 17, 18, 19). Table I (“Primary Essential Oil Constituents of Some Hop Varieties,” page 65) compares the levels of major oil components among several varieties selected to illustrate varietal differences.
Gas chromatography. One method of isolating the individual essential oils for analysis is gas chromatography (GC). This technology was invented in the early 1950s and has been used for hop identification since the 1960s (6). The essential oil profile of each variety is unique, and chromatograms provide a “fingerprint” that differentiates each variety (1, 15, 18, 19), particularly in the sesquiterpene region. As the technology has improved, the number of observable components has increased from 18 to several hundred. Gas chromatography essential oil profiles are now so accurate they can even detect small mixtures of varietal impurities within a sample (18).
All chromatograms will exhibit slight differences even for the same variety, which could be attributed to differences in climate, handling, storage, or experimental technique. This is why a data base of at least 20 chromatograph profiles from each variety is required to form a complete set of data showing all the expected variations (18). As mentioned previously, myrcene in particular deteriorates quickly with age, whereas levels of oxygen-containing compounds increase with storage and aging. Comparisons of the less volatile sesquiterpene levels and their ratios to one another (ratios to caryophyllene are most common) are thus more telling and are considered varietal traits.
The chromatograms shown in Figure 1 (opposite) offer an excellent visual representation of the hops listed in Table I. The chromatograms have been scaled and expanded to emphasize the sesquiterpene portion of the oil profile. The major peaks have also been aligned. Notice that the chromatograms are generally quite different, with the exception of Savinja Golding and Fuggle (which appear identical), and Tettnanger and Saazer (which appear similar yet have several differences). It’s generally believed that Savinja Golding and Fuggle originated from the same plant, so the fact that the chromatograms appear identical is hardly surprising. Tettnanger and Saazer are also generally regarded as being derived from the same rootstock.* One possible explanation for the variations between Tettnanger and Saazer is genetic differences that some researchers believe occur in land race hop varieties (see box, “Other Cases of Mistaken Identity,” page 63).
*One researcher has noted that Saazer may produce twice the farnesene content found in Tettnanger hops, even when grown side-by-side (2) Research varies on this point, however. Other analyses have been unable to differentiate the two varieties in terms of farnesene levels (1,4).
Because of the potential for variations and the difficulty involved in reading the overlapping data in a hop chromatogram, GC essential oil fingerprints are always used in association with other data. For example, both the Tettnanger and Saazer data in Table I show very similar farnesene, humulene, and selinene ratios (with respect to caryophyllene). Their alpha-acid content and alpha/beta acid ratios (not shown) are also similar. GC analysis alone is not enough.
Solid-phase extraction. The complexity involved in varietal identification demonstrates the need to standardize and clarify such data. One technique sometimes used to make chromatograms more consistent involves separating the oxygenated fraction from the hydrocarbon fraction using solid-phase extraction on silica (17). This technique makes it possible to view the hydrocarbon fraction separately, reducing the ambiguity caused by seeing both the hydrocarbon and oxygenated fractions on the same chart.
DNA fingerprinting — a new approach: The previously described techniques rely on comparing phenotypes (outward appearance) rather than genotypes (genetic makeup). GC analysis requires mature cones and cannot be used on immature plants. DNA typing (or DNA fingerprinting) has gained widespread scientific approval as a reliable way of directly identifying the genotype; see box, “The Forefront of Hop Identification” at left (20,21,22,23).
The genotype is a property of each cell, and is independent of environmental effects. The resulting profiles can be used to perform parentage and inheritance studies for breeding purposes. Because many hops are closely related, however, the problem is determining the relevant section of the DNA molecule to compare. New technology is helping with this analysis, and once perfected this new method of analysis promises to provide more accurate results using a semi-automated, field-based testing system, which would eliminate the need for a lab or even a highly skilled analyst.
Conclusions about U.S. Tettnanger
As GC essential oil analysis is becoming more routine, the libraries of varietal chromatograms at hop research centers around the world continue to expand. This research has produced some interesting results.
Most recently, Colin Green of the Hop Research Unit, Horticulture Research International (Wye, Kent) in England analyzed the essential oils of 15 varieties grown in the United States (1). As mentioned at the start of this article, Green determined that all 16 samples of the U.S. Tettnanger he tested were derived not from German Tettnanger, but from English Fuggle (U.S. Fuggles, incidentally, do not suffer from any transnational identity crisis — they are quite similar to their English ancestors). He based his conclusions both on the hops’ essential oil chromatograms and on their alpha- and beta-acid compositions. Chromatograms of various U.S. Tettnanger, U.S. Fuggle, and German Tettnanger samples are shown in Figure 2 (see page 66); numerical data is shown in Table II (above). The similarities between U.S. Tettnanger and U.S. Fuggle are quite obvious, as are the differences between U.S. Tettnanger and German Tettnanger.
Green went on to conclude that because his samples were obtained from two of the three major hop growing regions in the United States, much — if not all — of the U.S. Tettnanger crop was Fuggle. Australian Tettnanger (which originated from U.S. Tettnanger germplasm) and Australian Hallertauer samples also appeared to be Fuggle.*
These findings are consistent with earlier work by Anheuser-Busch research scientists Val Peacock and Paul McCarty, who could not reliably distinguish between Fuggle, Styrian Goldings, and U.S. Tettnanger using GC oil profiles (4).
David Hysert, technical director of the world’s largest hop merchant (John I. Haas) and president-elect of the American Society of Brewing Chemists, further confirms that all commercially available U.S. Tettnanger has an analytical profile similar to English Fuggle. His advice to brewers seeking Tettnanger with an analytical profile similar to German Tettnanger is to buy it from Germany (3).
Dr. Alfred Haunold, a hop researcher affiliated with the USDA Hop Research Station in Corvallis, Oregon (and the geneticist responsible for developing the Cascade and Willamette varieties), has known about the U.S. Tettnanger/Fuggle issue since the early 1980s (2). He believes that the most likely explanation for the affair is that initial German Tettnanger samples were planted in a field that was also used to grow Fuggles. It is likely that when samples were later selected from the field, growers chose from among the highest yielding plants, which turned out to be Fuggles rather than Tettnanger (unprofitably low yields are the primary obstacle to commercial production of traditional noble hops outside of their native regions).
*This research brings into question the issue of truth in labeling. In Europe, strict hop labeling laws were instituted by the EEC in 1977 to prohibit the sale of blended varieties (25). The law apparently does permit mixtures of some varieties from the same region for trade purposes; for example, Hallertauer Mittelfrüh and Hallertauer Gold may be present in one sample. Despite this, Green determined by GC analysis of essential oils that samples of so-called Tettnanger hops grown in Germany were actually mixtures of Tettnanger with either Hersbrucker Spalt or Hallertauer Mittelfrüh, which is not permitted under the regulations (18).
Whatever the explanation for Fuggles conquest of America’s Tettnanger crops, it appears that the subsequently named “U.S. Tettnanger” hop was released to growers before an essential oil verification test was performed, and that the original mistake was made during the early stages of propagation.
The largest consumer of U.S. Tettnanger — by an Olympic long shot — is Anheuser-Busch, Inc. The company became interested in U.S. Tettnanger in the 1980s and has been paying growers a small premium to produce it ever since. The company also arranged for the production of U.S. Tettnanger in other countries (it is grown in Tasmania and was trialed in New Zealand) as a precaution against outbreaks of disease among U.S. crops (a wise precaution, considering the recent outbreak of powdery mildew in the Yakima Valley).
The future of U.S. Tettnanger hops is now very uncertain. Anheuser-Busch’s contracts with U.S. growers expire this year, and, by all accounts, the company has no plans to renew. Doubtless many of the plants will be uprooted by growers to make way for varieties with better yields and more buyers. U.S. Fuggle and U.S. Tettnanger currently cost about the same, but both are more expensive than some of the more recently developed noble-type hops that have been bred specifically for American growing conditions, such as Mt. Hood, Liberty, Crystal, Ultra, and Santiam (12,26).
One last important point must be made: Even though U.S. Tettnanger takes after Fuggle more than it does its German namesake, Fuggle itself is really not a bad hop. In fact, Fuggle is about as close as one can get to a noble hop short of the land race originals or the new genetically engineered varieties. The only traits that really set Fuggle apart from the traditional noble hops are the alpha/beta ratio (too high, at around 1.8:1), and the cohumulone level (slightly too high, at 27%) (13). With an H/C ratio of about 3.1:1, it contains a respectable amount of humulene (which, as we mentioned earlier, is considered an important precursor of noble hop flavor) (1). Fuggle’s (and U.S. Tettnanger’s) low farnesene-to-caryophyllene ratios (0.5–0.8:1) also help to differentiate them from German Tettnanger (which are around 2.7:1), although Fuggle is still comparatively high in farnesene compared with most hops (see Table III, “Fuggle Versus the Nobles”).
It’s the Aroma that Counts
This article is certainly not intended to disparage U.S. Tettnanger hops. It is indeed a fine hop and, based on its chemical profile, it is close to being a true noble hop. Many brewers have used this hop over the past 15 years or so believing it to be of noble status and have been satisfied with the results.
It is this apparent satisfaction, in fact, that makes the current research so interesting. If brewers have been pleased all along with Fugglish Tettnanger, then it can perhaps be argued that the distinction between traditional noble varieties and other hop types stems more from historical bias than from practical benefit.
Regardless of the implications for nobility, it appears that end users can never be 100% sure of getting 100% of what they expect. Many varieties are very similar to one another and can easily be confused, from the time of propagation to the moment the hops are pitched into the copper, and in some cases it takes an expert in a laboratory to positively identify a sample. Fortunately, it is likely that quality control and consistency will improve in the future as varietal identification methods become cheaper and easier.
I am very grateful to Colin Green, Grey Leggett, Mark Thomas, Alfred Haunold, and Ralph Olson for their expert advice. Thank you also to Sonja Sherwood at BrewingTechniques, Jim Liddil, and Don Van Valkenburg for their contributions.
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