What is Hop Creep and How to Prevent It?

Hop creep is a phenomenon that refers to beer becoming over-attenuated due to additional diastaste 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 dextrins into fermentable sugars. This then 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 after packaging.

Hop creep can lead to a number of a problems such as;

• Lower final gravity (FG) than expected, which leads to

• Increased alcohol content, and other potential off flavours such as diacetyl, as well as

• Increased CO2, which can cause

• Over carbonated (pressurised) beer and potentially exploding bottles/cans

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

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.

Another 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 125-130F from the previous temperature of 145-150F. This reduction in temperature would mean 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-pressurised 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.
Whole cone hops 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 are known to reduce the impact and likelihood of hop creep.

Dry Hop Temperature

Recommended dry hop temperatures of 50 degrees fahrenheit (10 degrees celsius) or less to reduce or prevent hop creep. Warmer dry hop temperatures may promote it.
This is a general rule, but dry hopping several degrees below the particular yeasts recommended temperature range would also be an acceptable practice, since yeast activity would be potentially be minimised (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. 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 - and the more yeast that are in suspension the more likely hop creep is to occur when dry hops are added.

Package Yeast Presence

If yeast is removed from the beer prior to packaging, this can prevent hop creep from occurring. This may not be possible at a homebrewing level, and hop presence is necessary/desirable in certain commercial styles of beer, such as those that are hazy.

Removal of yeast by pasteurization is guaranteed to completely stop and prevent hop creep from occurring, given yeast are essential for it to occur.

Sterile filtration can also be used to reduce the amount of yeast in the fermented beer prior to 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 degrees celsius - but then after packaging the beer warms 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.

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