Image of Billy Goat Hop Farm
Article by Emily Wang, Founder/Lead Scientist at Fermly

Acronyms are all the rage in the brewing industry and could be considered a great divider between those who are interested in beer and those that are just there for a pint and a good time (but we are also there for that, too, right?). We all know the story behind the grand IPA, choose how we want to feel the next morning by ABV, and flavor profile by the IBU. Amongst brewers, there is the focus on OG, FG, TA, DAW, etc. A glossary is at the end in case you aren’t in the know yet.

All that being said, the latest and greatest of these in-your-face pronouncements of exception is DDH. Double Dry-Hop is taking the process of dry-hopping and going bigger and better! A usual dry-hop may be about four pounds of hops per barrel, but double that to eight pounds per barrel, and that beer is guaranteed to be a sensation! The brewer is impressive for developing the recipe and marketing is going to have a field day! Hop heads will be madly in love with it! It will sell out! It will be the best time ever!

But wait-why is the beer bursting out of the can when opening? It doesn’t taste right. Someone mentioned it tastes buttery-like; there is an oil slick on the top of their mouth. Touted as being full of orange and pineapple flavor, good thing no actual fruit was harmed in the making of the beer, but the brewer’s ego will be. Unfortunately, as brewers explored the expanding world of DDH beers, there was a drawback (hop) creeping up…

Double dry huh?
Before we can get to how hop creep happens, let’s start with the humble hop flower and its main role in the brewing process. Hops have many benefits to add to beer, but the main drive in adding this ingredient is the flavor/bitterness and aroma of the beer that is so appealing to consumers. Hop oil is an essential oil made up of hundreds of compounds, but only a few
volatile ones really matter when it comes to beer flavor: hydrocarbons (terpenes), oxygenated compounds, and sulfur-containing compounds. The source of this bitterness is based on the concentration of humulones (⍺-acids-terpenoids derived from terpenes), which are not bitter in and of themselves but undergo isomerization under heat to form the much adored
isohumulones (iso-⍺-acids) that provide the desired flavor. Hop utilization at different points during the brewing process can have a variety of outcomes because the volatile compounds that provide the flavor and aroma are lost or not fully utilized. This is a result of the stripping effects of CO2 or the absorption of yeast cells. Dry-hopping is meant to have fewer of these issues.

Dry-hopping put simply, is the cold extraction of hop oil compounds into an alcoholic solution (e.g., beer, obviously). Unlike hop additions during the brewing process, volatile compounds are preserved. Isohumulones are not formed, but instead, humulinones (oxidized ⍺-acids) develop. Humulinones provide less bitterness than their isomerized form. The result is all of the aroma and less of the bitterness that could put off the consumer. As the dry-hopping rates increase, it is now notable that the hop aroma is different from earlier additions. A hop that may result in spicy or floral notes during kettle hopping may be discovered to have a citrusy, piney, even dank aroma due to the cold addition.

Adding this extra step post-brewing comes with other bonuses like higher pH, ABV, and extract. Extract is a fancy way of saying the yeast ferments out sugar to produce everyone’s favorite compound: ethanol. In the process of dry-hopping, what isn’t always considered when adding the hops is that there are enzymes being added as well. During the initial hop addition of the brewing process, these enzymes do not matter because they are most likely denatured due to the heat. These dextrin reducing enzymes break down unfermentable residual sugars from earlier in the brewing process during cold addition. The hope is when hops are added, fermentation is done, but what if it’s not?

What’s hoppinin’?!
The yeast goes after the new sugars in a secondary fermentation, which we now refer to as hop creep. The yeast starts pissing alcohol and burping CO2 again. Once, this was done on purpose. Towards the end of the 19th century, hops were added to casks of beer to trigger this secondary fermentation. The main benefit of this practice was drying out the beer, making it
more effervescent and microbial, as well as adding flavor stability. This is no longer the goal. Increased alcohol content beyond what the customer is told is not really okay, but the bigger concern is the increase in gas that results in over-pressurization of packaging. The last thing any brewer or consumer wants are cans and bottles busting open on shelves. Refermentation can vary depending on the beer, with drier beers that have low dextrin content for the yeast faring better.
Many brewers include additional adjuncts to keep beers hazy if the polyphenol content does not maintain the preferred haze, providing another source of sugars for the yeast to use when reduced to fermentable form. Timing of the dry-hopping is of crucial importance when considering the hop creep phenomenon, which has been suggested to increase the presence of
an off-flavor.

Hop creep’s spinoff: Diacetyl
Fermentation results in many compounds and not all of them are as enjoyable as others. Diacetyl is an off flavor that many individuals are sensitive to and is undesirable in beer. It presents as a buttery flavor, which may be accompanied by an oil slick feeling in the mouth. Yeast produces this compound during fermentation, and in anticipation of this event, brewers plan for this. This step is called, aptly, a diacetyl rest, so the yeast can clean up the mess it made. Hop creep does not accommodate for this. The secondary fermentation results in the presence of diacetyl again. The yeast may still clean up, but it will be much slower than during primary fermentation if it occurs at all. The flavor threshold for diacetyl is low (around 0.1 ppm) and is completely out of control of the brewer if this occurs in packaging. Like most things in life, the goal becomes the prevention of this situation. A quick bit of advice from Patrick Combs, Quality Manager at Weldwerks Brewing Co.: “...worry less about pitch rates and more about accurate daily gravity readings until you understand your hop lots.”

The sequel is never as good as the original.
Secondary fermentation is avoidable and there are several methods that can be used as preventive measures. There is also the option to not dry-hop, but consumers most likely would not prefer that so here are a few methods

● When and how to hop: A brewer could feasibly move some of the hops from the dry-hopping step to earlier in the brewing process since temperature has been shown to denature the enzymes and make them less functional. One could also consider
performing the dry-hopping step closer to the initial fermentation to give the enzymes and yeast an opportunity to work through the sugars and diacetyl. Choices in this realm must be carefully considered for how they will affect bitterness and aroma but may be preferable to losing a batch. “We moved the dry-hop earlier into fermentation so that there was more active yeast present to consume any sugars made available by the hop enzymes, and to clean up any VDK produced by this additional fermentation,” according to Amanda Oberbroeckling, Lap and Quality Assurance Manager at 4 Noses Brewing.
“We also dry-hopped after a soft crash of a few degrees, instead of dry-hopping colder, as the warmer temperatures allowed for the yeast to stay more active and to perform the additional fermentation promoted by the addition of hops.” If a brewer is going to dry-hop, Combs details “I would caution any brewery that is doing a large warm dry hop addition to take careful dailies until they know those lots well. When a new lot is selected, be prepared for it to behave differently than the previous crop year.”

● Incorporate the creep into the process: As brewers understand how hop creep functions, it also offers the opportunity to decide if it is something that can be planned for. “It wasn’t so much an attempt to avoid hop creep as much as it was an attempt to contain it,” says Combs. “These enzymes exist in the hop material, and they are going to act upon their target substrate. The goal was always to ensure that the beer was truly stable for at least 2 days post dry-hop and passed a sensory-based forced VDK before we crashed.”

● Cold storage: When kegs are sitting in the cold room, it is easy to prevent or not worry about secondary fermentation since yeast and enzymes are not a fan of lower temperatures. That being said, this is far more difficult when packaging for distribution on the shelf which may or may not be warm. Telling clients to keep the beer cold probably won’t be a guaranteed option and exploding cans are a great way to get them to not carry that brand (or the brewery anymore). We all love beer, but let’s leave the janitorial work to the brewer, not the customer/client.

● Add sulfites/sulfates: A method that used in the wine industry, the addition of sulfites inhibits yeast activity. DO NOT confuse sulfites with sulfides, the source of off aromas like rotten eggs or dirty gym socks. Sulfites are a natural byproduct of the yeast during fermentation, but adding sodium metabisulfite supplies additional free sulfur dioxide to enter the yeast cell. Increasing the presence of free sulfur dioxide displaces other compounds during reactions, causing a disruption of the enzymatic and protein activity within the cell. However, sulfites have come under a great deal of scrutiny due to
potential health concerns, since a part of the population is believed to be sensitive to it and experience allergic reactions.

● Filter the beer: Removal of the yeast from the beer is a great way to prevent fermentation but may come with the unfortunate problem of removing other desirable aspects depending on the style of beer. The beer could be filtered prior to dry-hopping, but this doesn’t seem to be a common practice.

● Pasteurize the beer: This is an ideal albeit expensive method to employ. Pasteurizing the beer is pretty much guaranteed to kill off the yeast and debilitate enzymatic activity. Still, the cost of buying or having access to a pasteurizer may prove more problematic than it is worth.

● Hop kilning temperature: As keeps being mentioned, temperature matters, and this step is no different in that respect but does not occur at the brewery. The hop provider must put the flowers in a kiln because by increasing the temperature, there is a tremendous decrease in the dextrin-reducing enzymatic activity during dry-hopping. The cost of increased temperatures during kilning is hop oil loss, requiring more hops to meet the same aroma standard that is desired. It is also important to keep in mind per Oberbroeckling: “It varies from hop to hop, crop year to crop year, and even farm to

There are many methods for avoiding or mitigating hop creep, but it may be unavoidable. “There's no one way to solve this problem, so there's a lot of anecdotal information to decipher before making decisions for your own brewery,” describes Oberbroeckling. “What worked for your neighbor may not work for you, but you don't really know until you try it.” This is where the most critical aspect of beer comes into play: someone is supposed to drink it. If a consumer wants to enjoy a NEIPA DDH, they should drink it sooner rather than later. The hop pop of the aroma decreases with age noticeably, making these beers not great for cellaring, and of course, there is an increased chance of hop creep. Innovation keeps pushing the exploration of hops and their role in beer further, so we might learn something new! Many breweries encourage customers to drink their current explorations into hop character sooner rather than later, so haze bros best get to cracking those cans open FFS.

Glossary (abridged version) to acronym like a pro!
AA-Alpha acids
ABV-Alcohol by volume
APA-American Pale Ale
DAW-Deaerated water
DME-Dry malt extract
DMS-Dimethyl sulfide
ESB-Extra Special Bitter
FG-Final gravity
IBU-International Bitterness Units
IPA-India Pale Ale
IYKYK-If you know you know
NEIPA-New England India Pale Ale
OG-Original gravity
SG-Specific gravity
SRM-Standard Reference Method
TA-Titratable Acidity


About the Author
Emily received her Bachelor of Science in Biology and Chemistry from Le Moyne College in 2009. Having always nurtured a passion in microbiology and chemistry, Emily has always enjoyed being in a laboratory environment. Her altruistic nature and desire to care for others gave her eight years of success in the medical field and acceptance into medical school. After choosing to forgo medical school, Emily moved to Colorado looking to rekindle her passion for the laboratory sciences. After a hard weekend of enjoying craft beers, Emily decided to grab life by the pint glass and founded Fermly in 2018. Emily is a Certified Beer Server in the Cicerone program and a provisional BJCP judge.