Hop creep is a common term used to describe the excessive attenuation of beer that has been dry-hopped. It can be considered as an unwanted secondary fermentation that occurs sneakily, leading to a decrease in gravity, causing a spike in diacetyl levels, and resulting in higher alcohol content and CO2 production.
Hop creep can develop slowly and subtly. If a dry-hopped beer is not properly monitored or controlled, it can undergo refermentation after leaving the brewery. This means that unsuspecting consumers may notice it first through a buttery flavor, higher alcohol content than stated on the label, or, more problematically, overpressurization that causes bottle caps to pop or cans to explode.
What Causes Hop Creep?
Research on hop creep was initially published in 1893 but was forgotten until the mid-2010s when the popularity of dry-hopped, often hazy, IPAs brought it back into focus. Modern science supports the hypothesis proposed by 19th-century experts: refermentation occurs when diastase enzymes in hops interact with unfermentable carbohydrates in the presence of active yeast.
This is particularly problematic for hazy or juicy beer styles with high yeast counts and hopping rates.
Do All Hops Lead to Hop Creep?
Experiments have shown that while different hop varieties perform similarly in a soluble starch solution, their behavior differs in real-life dry-hopping trials. The maturity of the plant or cone, farming conditions, and handling and processing during and after harvest heavily impact the hop creep activity of each variety.
Can Hop Creep Be Prevented?
The main factors affecting refermentation in dry-hopped beers are hop contact time, the amount of active yeast, and temperature. A technical brief published by the Brewers Association suggests that warmer dry-hopping temperatures and longer exposure time increase the formation of fermentable sugars. Heat-treating hops before dry-hopping can deactivate their enzymatic activity.
While it may not be possible to prevent hop creep entirely, it can be monitored, reduced, and controlled. Brewers can monitor overattenuation by measuring alcohol content and specific gravity. They can decrease the likelihood of hop creep by using recipes that produce higher fermentation worts or by intentionally underattenuating their beer to account for the effects of hop creep. Other preventive measures include adding some hops to the whirlpool before fermentation, filtering or pasteurizing the liquid, adding alpha acetolactate decarboxylase enzymes to reduce diacetyl formation, or ensuring an unbroken cold-chain distribution system.
Another strategy is to minimize the contact between hops and beer.
Furthermore, researchers have found that shorter dry-hop times result in more fruity aromas, while longer dry-hopping times produce polyphenolic herbal notes.
Considering contact time as a way to mitigate hop creep when using high hop loads, it may be necessary to consider how long the beer is left on hops.
Should You Slow Down or Speed Up Hop Creep?
Temperature can be manipulated to either slow down or speed up hop creep, and brewers generally prefer one approach over the other. They can encourage hop creep to occur in the tank instead of surprising consumers by forcing the fermentation to develop during the production process. Alternatively, they may create cool conditions that minimize hop creep formation.
Dry hopping at 50°F (10°C) instead of 68°F (20°C) for one to two days resulted in the production of fewer fermentable sugars.
One option is to “dry hop warm with extended contact time to encourage any hop creep to happen in the tank until VDK tests are passed,” as referred to by the vicinal diketones family of flavor compounds that include diacetyl. “The other option is to dry hop at a cooler temperature and for a shorter duration to reduce overall enzymatic activity. Essentially, there is less chance of hop creep when dry hopping is done at lower temperatures and for a shorter period.”
The author states that the cooler dry-hopping method has never failed.
While hop creep is still being studied to understand its causes and effects, it is a complex phenomenon influenced by various factors. One of the best ways to manage its effects in a brewery is to closely monitor key parameters. Taking pH, gravity, and VDK counts before dry-hopping and comparing them with ongoing measurements afterwards can provide insights into how hop creep might affect a specific beer and, more importantly, how long it persists. If hop creep is suspected, detailed quality control analysis is essential.