Get to Know the Synergy of Survivables

Knowing the aroma compounds that better survive the brewing process—and how best to use those that don’t—can help brewers get more from their hop additions and blends.

Source: Yakima Chief Hops poster, “Survivable Compounds”

Never mind IBUs. How many AUs were in that last IPA you brewed?

Almost 30 years ago, Gail Nickerson at Oregon State University and Earl Van Engel of Blitz-Weinhard Brewing proposed establishing an Aroma Unit comparable to the International Bitterness Unit. They identified 22 hop compounds that would be used to calculate the Aroma Unit and divided them into three broad categories: oxidation products, floral-estery compounds, and citrus-piney compounds.

The concept was seen as controversial and never found broad acceptance. Nonetheless, it gave brewers a new way to think about hop aroma at the outset of the 21st century, just as interest was expanding in the broader range of flavors and aromas that hops can produce. As the authors wrote, “Hop-oil analyses that emphasize varietal identification do not provide results that the brewer can use to control hop aroma because the major hop-oil constituents are not present in beer.”

Put another way, the hydrocarbons that make up as much as 80 percent of essential hop oil are not water-soluble and do not survive the brewing process. The fruity, tropical, exotic, add-your-own-adjective aromas and flavors that define fashionable hop-centric beers result from compounds that do survive and are not so easily measured. Some of those were part of the AU, but scientists have discovered the role that others play only recently. The number of compounds identified in hop oil has expanded from about 250 in 1990 to almost 1,000 today.

Surviving and Thriving in Beer

Yakima Chief Hops has chosen seven aromas and flavors that make their way into beer and labeled them “survivables.” They were picked based on research—using equipment found in few other laboratories around the world—that was also used to create TRI 2304CR, a blend recently released as Cryo Pop. As the name suggests, YCH uses the same cryogenic hop-processing technology it introduced in 2017 for individual varieties to produce the lupulin-rich, blended pellets.

As part of the promotion rolling out Cryo Pop, YCH published a 30-page Survivable Compounds Handbook and poster that are also available to download. “This is intended to be more of a brewer tool ... than a novel piece of research,” says Spencer Tielkemeier, Yakima Chief’s brewing-innovations lead. “The more we looked at this graph, the more we realized it has practical insights for brewers.”

A Visual Tool

The poster presents varieties based on the sum of the survivables but also makes it easy to visually compare the potential impact of individual compounds. (For the record, not all compounds are measured the same way; some are measured in parts per million, and others are measured based on area counts per microgram.)

The compounds include two monoterpene alcohols (linalool and geraniol), four ketones or esters (2 nonanone, 2-methybutal isobutyrate, methyl geranate, and isoamyl isobutyrate), and one polyfunctional thiol (3-mercaptohexanol). (See separate descriptions, below.)

The chart is far from comprehensive; it mainly features the most popular hop varieties that YCH farmers grow. However, the lessons to be learned also apply to the wider universe of hop cultivars. For instance, early research shared by YCH found that Bravo, Mount Hood, and Millennium are among the varieties richest in survivables.

“We’ve shied away from giving brewers practical advice,” says Tielkemeier, who spent eight years as a brewer before joining YCH. Constant waves of new varieties changed that approach. “Brewers don’t have time ... to find the exact sweet spot for each new hop.”

YCH includes four specific suggestions on its poster:

• Use hops that are higher in survivables earlier in the brewing process. An example of this would be using Idaho 7 in the whirlpool.
• Use hops that are lower in survivables later in the process, such as post-fermentation dry hopping. YCH offers Cashmere as an example, but Azacca is another excellent choice.
• Blend hops to maximize beneficial concentrations. For example, because Loral is high in linalool and Talus is high in geraniol, the two are candidates for blending. In contrast, Loral and Crystal are high in linalool, but offer little difference from each other.
• Load the wort stream with survivables early. High concentrations of survivables in the whirlpool and during active-fermentation dry hopping create the conditions for biotransformations. YCH suggests, for example, Idaho 7 in the whirlpool and Sabro and Simcoe during active fermentation.

“We will all benefit if we get brewers talking about solubility,” says Tielkemeier. Yet he understands that brewers keep coming back to the question, “What about biotransformation?”

He says that the Cryo Pop blend created by their R&D teams is an excellent whirlpool product, but he quickly adds and emphasizes, “It is an active-fermentation product. It works best in active fermentation.”

In other words, the blend will benefit from biotransformations. Considering when to make additions, he says, is “just as much about what you are subtracting as what you are adding.”

Masking and Biotransformations

Restated: Masking may alter the impact of biotransformations. Brewers use the word biotransformation to mean much more today than in 2003, when Andrew King and J. Richard Dickinson first described the modification of an aromatic compound into another aromatic compound during fermentation. The best known is the transformation of monoterpene alcohols, specifically geraniol, to citronellol.

More recently, brewing scientists have focused on the breakdown or release of non-aromatic compounds that result in additional aromatic compounds. This may include hydrolysis of glycosides or the release of bound thiols. More research about the latter, particularly related to active fermentation, is underway—and we will address that in an upcoming article.

Discussing subtractions, Tielkemeier is referring to compounds that are not survivable. For instance, YCH analyzed more than 30 hop varieties following the 2019 harvest, finding that Sorachi Ace contained the largest percentage of essential oil. However, it had the second-lowest number of survivable compounds because most of that oil was made up of hydrocarbons—specifically, myrcene.

Myrcene, which smells herbal and woody, may constitute 70 percent of the oil in popular varieties. The boiling process basically eliminates it. If you are dry hopping, active fermentation mostly removes it, too. However, if you add it post-fermentation, its aroma is more likely to survive and, thus, mask other more subtle character.

When craft brewers began dry hopping in earnest in the 1990s, Gerard Lemmens—an influential hop-industry veteran—suggested that brewers should open the hop bag 24 hours before dry hopping, to let the myrcene “blow off.” He found its aroma unpleasant.

However, at the 2008 Craft Brewers Conference, Tom Nielsen of Sierra Nevada used myrcene as an example of how brewers can calculate the “odor activity value” (OAV) the same way that food scientists do with other aroma compounds—by dividing the concentration of a compound by the threshold for perception of that compound.

Myrcene has a threshold of about 30 parts per billion, and Nielsen said that 400 parts per billion of myrcene—or more than 13 times OAV—was a good target if aiming to create a strong, piney, resinous, highly hopped American beer. (He definitely was not describing Hazy Little Thing.)

To return to Nickerson and Van Engel: In 1992, they wrote that since the 1960s, “scientists have tried to identify the compounds responsible for hoppy character in beer without success. Hoppy aroma in beer is probably not attributable to a single component but rather to the synergistic effect of several compounds.”

The seven compounds that Yakima Chief Hops has singled out clearly are not the only ones that contribute to hop aroma. However, finding that a combination of monoterpene alcohols, esters, and a thiol survive the brewing process—and create more intense aromas and flavors that none possess individually—is convincing evidence of the importance of synergy.

The Seven Survivables

Geraniol
Most terpenes in hops, such as myrcene, are volatile and do not survive the brewing process. Because they are oxygenated, monoterpene alcohols are more likely to end up in beer. As its name suggests, geraniol may smell geranium-like as well as citrusy. It may also be transformed into citronellol during fermentation, creating a new compound that contributes to tropical aroma.

Linalool
Like geraniol, linalool is a monoterpene alcohol. Much of it will be lost during the boiling process, but it is soluble in beer and will survive the whirlpool and active fermentation. It was established more than 50 years ago as the compound associated with “hoppy” flavor, although it was already understood there was no one marker. On its own, it is fruity in aroma and flavor, reminding some of Froot Loops.

2-nonanone
An aromatic ketone, 2-nonanone at its best smells sweet and fruity but may be buttery or waxy.

2-methybutyl isobutyrate
A primary ester in hops, 2-methybutyl isobutyrate is one of the most prominent volatiles. It’s aroma is fruity, specifically apricot.

Isoamyl isobutyrate
Isoamyl isobutyrate is an ester that also contributes fruity character, including apricot.

Methyl geranate
Likewise, methyl geranate is another fruity and floral ester.

3-mercaptohexanol (3MH)
A thiol that may smell tropical and of grapefruit, 3-mercaptohexanol (3MH) may also be converted into 3-mercaptohexylacetate (3MHA), adding passion-fruit flavor.

Stan Hieronymus