Hops have long been evaluated through aroma and bitterness. That framework no longer reflects how hops behave in modern brewing.
As dry hopping has become central to many beer styles, brewers are increasingly exposed to unintended re-fermentation, variability in final gravity, and instability in package. These effects are not random. They are driven, in part, by enzymatic activity present in hops.
This article by Francesco Lo Bue and Philip Wietstock, Professor and Head of the Chair of Brewing and Beverage Technology at TU Berlin, brings together recent research on hop diastatic power with observations on enzyme distribution within the hop cone, to provide a more complete understanding of how hops influence fermentation beyond flavour.
Hops as enzymatically active raw materials
Hops contain enzymes capable of degrading dextrins into fermentable sugars, including:
- α-amylase
- β-amylase
- α-glucosidase
Under dry hopping conditions, these enzymes remain active. In the presence of yeast, they can generate fermentable extract and trigger renewed fermentation.
This process, commonly referred to as hop creep, can lead to:
- Increased alcohol beyond specification
- Overcarbonation and associated safety risks
- Reduction in body due to dextrin breakdown
- Formation of additional yeast-derived flavour compounds
- Extended production timelines
Although enzymatic activity in hops is significantly lower than in malt, its impact is amplified by when it occurs, late in the process when beer is assumed to be stable.
Measuring enzymatic potential: hop diastatic power
To quantify this behaviour, a method has been developed to measure hop diastatic power (HDP) as a functional indicator of enzymatic activity.
The approach:
- Uses potato starch as a substrate
- Incubates hops under controlled conditions
- Quantifies glucose and maltose formation via HPLC
Results are expressed as:
- µmol glucose equivalents per hour per gram of hops
Potato starch was selected due to its strong correlation with what occurs during dry hopping and its alignment with established malt diastatic activity methods.
Alongside HDP, individual enzyme activities can be measured. Among these, β-amylase shows the strongest correlation with overall diastatic power, indicating a central role in dextrin degradation during hop creep.
Range and practical interpretation
Across multiple datasets:
- Hop diastatic power typically ranges from ~13 to 90 HDP units
For example, Cascade from The Spanish Yard shows:
- HDP: 37.8 ± 1.95
- Moderate enzymatic activity
This places it in a range where it can generate measurable amounts of fermentable sugars and contribute to hop creep under standard dry hopping conditions.
A key observation is that enzymatic activity does not correlate with traditional hop classification. Both aroma and bittering varieties can exhibit low or high enzymatic potential.
Variety is currently the dominant factor, while crop year and agronomic conditions introduce additional variability that remains difficult to predict.
Enzyme distribution within the hop cone
While HDP defines the magnitude of enzymatic activity, it does not explain where this activity originates within the hop structure.
Recent work has measured enzymatic activity across hop cone fractions:
- Lupulin glands
- Strig (central stem)
- Vegetative material (bracts and leaf tissue)
The results are consistent:
- Vegetative material and strig show higher enzymatic activity than lupulin
This creates a clear separation between functional contributions:
| Fraction | Primary Contribution |
| Lupulin | Aroma compounds and α-acids |
| Vegetative material | Enzymatic activity |
This explains why aroma intensity and enzymatic potential are not directly linked.
Implications for Brewing Practice
1. Enzymatic activity is independent from aroma
High oil content does not imply high enzymatic activity. Treating hops as a single functional input overlooks this distinction.
2. Hop creep is structurally influenced
Hop creep is not only driven by process conditions such as temperature, yeast presence, or dry hop rate. It is also influenced by the proportion of enzymatically active material in the hop product.
3. Hop format affects fermentation behaviour
Because enzyme concentration varies across hop fractions:
- Higher vegetative content → higher enzymatic load
- Lupulin-enriched products → lower enzymatic load
This positions hop format as a relevant parameter in fermentation control, not just flavour design.
4. Processing does not eliminate enzymatic activity
Pelletisation and typical storage conditions have limited impact on enzymatic activity. The enzymatic potential present in raw cones is largely retained in finished hop products.
5. Variability remains a key challenge
Enzymatic activity varies with:
- Variety
- Crop year
- Cone fraction composition
As a result:
- Two batches of the same variety can behave differently
- Current hop specifications do not capture this variability
Why is this not yet standard in hop specifications
Despite its relevance, enzymatic activity is not currently included in standard hop Certificates of Analysis.
This is due to:
- Lack of globally standardised methods
- Analytical complexity at low activity levels
- Historical focus on aroma and bitterness
- Strong dependency on brewing conditions
However, as dry hopping becomes more widespread and process consistency more critical, the need to quantify enzymatic behaviour is becoming increasingly clear.
Conclusion
Hops are not passive ingredients. In addition to contributing aroma and bitterness, they introduce enzymatic activity that can modify beer after fermentation.
Understanding and quantifying this activity through parameters such as hop diastatic power, alongside structural considerations such as cone fraction composition, provides brewers with an additional layer of process control.
As the industry continues to refine dry hopping practices, enzymatic activity is likely to move from a research topic to a practical specification parameter.
References
- Wietstock, P. C.; Michalek, D.; Treetzen, T.; Barreto Carvalhal Pinto, M.; Biendl, M.; Gibson, B. Diastatic Activity of German Hop Cultivars with Respect to Variety, Crop Year, and Separated Hop Cone Parts. ACS Food Sci. Technol. 2025, 5, 2408–2416.
- Wietstock, P. C.; Lützenberger, T., Biendl, M.; Gibson, B.
 A Method for the Determination of Hop Diastatic Power – Part 1.
 BrewingScience 2021, 74, 92-99. - Wietstock, P. C.; Winter, F.; Michalek, D.; Biendl, M.; Gibson, B.
 A Method for the Determination of Hop Diastatic Power – Part 2.
 BrewingScience 2022, 75, 37-43.
Francesco Lo Bue says: I would like to thank Philip Wietstock for co-authoring this article.
Philip Wietstock is Professor and Head of the Chair of Brewing and Beverage Technology at TU Berlin. His work focuses on understanding how raw materials, particularly hops, behave beyond traditional analytical parameters, and how this influences brewing performance in practice.
