From Fermentation to Dry Hop: The Shifting Fate of Esters

By Dave Shapiro, Dip Brewery Engineer & Product Developer at Evodia.

Along with terpenes, esters play a large role in defining beer and hop character. These fruity compounds, built from the condensation of acids and alcohols, are soluble, volatile, and often have remarkably low sensory thresholds. A small change in concentration can mean the difference between muted aroma and explosive fruit character. For brewers, esters sit at the crossroads of raw materials, fermentation, and process. 

In beer, the vast majority of esters produced by yeast are ethyl esters. Here, ethanol is abundant and acts as a universal building block, combining with a wide range of acids (from acetic acid to long-chain fatty acids) to generate flavors that range from solventy and pear-like to tropical and candy-like. Hops exist in a very different chemical environment. Ethanol is scarce in the cone, and as a result, methyl esters dominate. These methyl esters can take the harsh, cheesy, or even pukey acids found in hops and transform them into surprisingly pleasant pineapple, melon, and tropical notes.

Not all esters behave the same in beer. In fact, size matters. As ester molecules get larger, they become more hydrophobic and their sensory character tends to skew fruitier and riper. Unfortunately, those same properties make them vulnerable during dry hopping. Multiple studies have shown that these larger, more hydrophobic esters are preferentially lost during dry hopping, likely due to adsorption onto the resinous, vegetal hop material itself.  

Hop enzymes have been getting a lot of attention in recent years as the phenomenon of hop creep returned to focus for many brewers. What started as a discussion around amylolytic enzymes quietly producing fermentable sugars has expanded into something broader and more interesting. As researchers have looked closer, a much more diverse enzymatic toolkit has begun to emerge. A recent study by Willemart, Tanriverdi, and Collin (2025) highlighted the role of hop-derived esterases and their impact on beer aroma during dry hopping. In their work, yeast-derived ethyl esters such as isoamyl acetate steadily declined with increasing dry hop contact time. While the samples were held for up to 21 days (longer than most commercial practices) the takeaway is hard to ignore: hop esterases are active, soluble, and capable of reshaping ester profiles long after fermentation is complete. 

At first glance, this paints dry hopping as hostile territory for yeast-derived esters. Between adsorption to hop material and enzymatic hydrolysis, some of fermentation’s most prized fruity compounds are steadily eroded. But hops are not just takers, they are also makers. Alongside ester loss, hops bring their own array of ester-driven flavors into beer. Many of these compounds are extracted directly during dry hopping and are strongly associated with the character of certain varieties, such as Huell Melon. 

As researchers began measuring transfer rates of hop volatiles into beer, something unexpected emerged: for some ethyl esters, apparent transfer exceeded 100%. In other words, more ester was present in the beer than could be accounted for by extraction from hops alone. This raised a critical question: where were these esters coming from? Possible explanations included yeast metabolism, non-enzymatic chemical reactions, or previously unrecognized hop enzymes. 

Work by Brendel, Hofmann, and Granvogl (2020) provided a compelling piece to this puzzle. Using a model system that mimicked dry hopping in a nearly alcohol-free beer (0.05% ABV), they suggested that hops could actively induce the formation of ethyl esters. The fact that this occurred in the absence of yeast strongly implicates hop-associated enzymes rather than fermentation metabolism. Even more striking, ester formation persisted at ethanol levels relevant to low- and non-alcoholic beer, highlighting that these reactions are not limited to conventional strength styles. 

Taken together, these studies suggest that dry hopping is not merely an extractive process, it is a chemically and enzymatically active phase of beer production. Yeast-derived esters may be lost, transformed, or hydrolyzed, while hop-derived acids and enzymes simultaneously create new ethyl esters with powerful fruity expression. The final aroma is not simply the sum of hops plus fermentation, but the result of competing pathways of destruction and creation. 

Personally, I love that the rabbit hole of beer has no bottom. From the earliest days of brewing science to today, beer continues to reveal new layers of complexity. Each advance answers one question and raises three more. Though the uncertainty is frustrating when consistency is the goal, it is also what makes beer such a compelling medium. In the space between raw materials and the finished product, quality and character are always being negotiated, not dictated.