Tuesday, 1 April 2025

Understanding Hop Creep: Causes, Effects, and Prevention

Introduction to Hop Creep

Hop creep is a phenomenon that refers to beer becoming over-attenuated due to additional diastase enzymes being introduced to the wort/beer when quantities of hops are added for dry hopping. These enzymes can cause the conversion of long-chain unfermentable dextrin's into fermentable sugars. 

This results in what is essentially another slow, "mini" fermentation that kicks off after the primary fermentation has completed and dry hops are added. The problem isn't just isolated to the period that the beer is in direct contact with the dry hops either. The enzymes that are introduced by the dry hops remain in the beer even after they are removed (or the beer is racked off them) - meaning hop creep can occur very late in the beer production process, sometimes even after packaging.

Symptoms of Hop Creep

Hop creep can lead to several problems, including;

  • Lower final gravity (FG) than expected, which leads to
  • Increased alcohol content and other potential off-flavors such as diacetyl
  • Increased carbon dioxide (CO2) which can lead to;
  • Over carbonated (pressurized) beer and potentially exploding bottles/cans

As you can see, all of the potential issues are connected, and the last point can be particularly dangerous to consumers and homebrewers alike.

Causes of Hop Creep

Hop creep often occurs after packaging meaning the first people to notice it are often the end customers when they experience a product that does not necessarily match what is printed on the label.

The concept isn't new - it was first documented as far back as 1893, but was seemingly forgotten about until recent times with the increased popularity of aggressively dry-hopped craft beers.

One speculative factor for the recent increase in prevalence of hop creep is the dropping of hop kilning temperatures. At the direction of the craft beer industry, the hop industry over the past five years have dropped their kilning temperature to an average of 125-130°F (51.7-54.4°C) from the previous temperature of 145-150°F (62.8-65.6°C). This reduction in temperature means less of the hop enzymes are inactivated during kilning.

The hop creep process is known to be slow - hence the term 'creep', and may only result in a one or two gravity points of difference from the expected terminal gravity of the wort - but this could have big implications in terms of alcohol content and CO2 production. The common off flavour, diacetyl, is also created again by this secondary mini fermentation, and can take longer to be cleaned up the yeast again, if at all.

From a commercial perspective, hop creep could cause potentially expensive or damaging product recalls if the product is found to not match the stated alcohol levels, or if vessels (cans or bottles) may be over-pressurized and at risk of exploding.

How to Prevent Hop Creep

There are a number of factors that are known to reduce (or promote) the occurrence of hop creep;

Hop Form

  • CO2 extracts and cryo pellets are less susceptible to causing hop creep.

T-90 hop pellets are less likely to cause hop creep compared to whole hop cones

  • Whole hop cones are more susceptible to causing hop creep as it is believed the associated enzymes are linked to the green matter of hops which are more prevalent in whole cones.

Dry Hop Duration

  • Shorter dry hop durations reduce the impact and likelihood of hop creep.

Dry Hop Temperature

  • Recommended dry hop temperatures of 50°F (10°C) or less to reduce or prevent hop creep.

  • Warmer dry hop temperatures may promote hop creep.
  • Dry hopping several degrees below the yeasts recommended temperature range would also be an acceptable practice, since yeast activity would be minimized (or eliminated) if the wort is too cold.

Dry Hop Amount

  • Low dry hop loads (less than 2 pounds per bbl (barrel) or approx 6.5g/L) is recommended to reduce hop creep. 

Large dry hop loads like this one can increase the risk of hop creep occurring

  • Greater dry hop amounts may increase hop creep risk and severity.

Fermenter Yeast Load

  • Hop creep can only occur with active yeast in suspension of the beer.
  • The more yeast that are in suspension the more likely hop creep is to occur when dry hops are added.

Package Yeast Presence

  • Remove yeast from the beer before packaging can prevent hop creep (though this is not always possible at a homebrewing level).
  • Pasteurization can completely stop and prevent hop creep by removing yeast.
  • Sterile filtration can also reduce the amount of yeast in the fermented beer before packaging.

Conclusion

We believe there is still more research and information to be uncovered in regards to understanding everything about hop creep. One question we still have is whether hop creep is likely to occur if you dry hop under the recommended 10°C, but after packaging allow the beer to warm up again since it has been stated that the enzymes that cause hop creep remain active in the beer even after the hops themselves have been removed.

What can be concluded though, is that hop creep is real and that brewers should at the very least be aware of it and can opt to take measures to combat it if they choose. For some, a few extra gravity points and higher alcohol content may be beneficial - but the potential side effects like diacetyl production and excess CO2 should also be taken into consideration, especially if packaging into bottles.

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