Dry hopping brings out incredible hop aromas and flavors in American craft beer, but it can also introduce unexpected challenges—one of the most common being vicinal diketones (VDKs). These compounds, especially diacetyl (butane-2,3-dione) and pentane-2,3-dione, can create buttery, creamy, or butterscotch-like notes that most brewers want to avoid, particularly in lagers and hop-forward ales.

What Are VDKs and Why Do They Matter?

VDKs are flavor-active compounds with very low taste thresholds, meaning even trace levels can impact your beer’s sensory profile. While a touch might be acceptable in certain traditional styles, excessive diacetyl is usually seen as an off-flavor, detracting from the clean, crisp character prized in many US beer styles. That’s why monitoring and managing VDKs is crucial for brewers aiming for consistent, high-quality results.

How to Test for Diacetyl in Brewing

A practical way to monitor VDKs during beer maturation is the diacetyl force test:

1. Draw two 100 ml samples from the maturation tank.
2. Cover both samples to prevent aroma loss.
3. Leave one at room temperature.
4. Heat the second sample to 149°F (65°C) for 20 minutes, then cool to 68°F (20°C).

This heat treatment converts precursors into detectable VDKs. By comparing aromas, brewers can determine if the beer is ready for the next step or if more maturation is needed. However, this method depends on the tasters’ sensory abilities, which can vary based on health, diet, and even time of day. For the highest accuracy, gas chromatography (GC) testing is preferred but is typically available only in large, specialized breweries.

How ALDC Enzyme Helps Control Diacetyl

To gain tighter control over diacetyl and other VDKs, many US breweries are now using the enzyme alpha-acetolactate decarboxylase (ALDC). Here’s how ALDC makes a difference:

• Prevents Diacetyl Formation: ALDC converts precursors before they turn into off-flavors.
• Speeds Up Maturation: Shorter tank times and faster turnaround for your beer.
• Boosts Flavor Consistency: Delivers clean, reliable flavor in every batch.

Beware of Hop Creep

Dry hopping can reactivate yeast and create additional fermentable sugars, a phenomenon known as hop creep. This can trigger renewed diacetyl production if not managed properly. ALDC helps prevent these issues, but brewers should also monitor attenuation and maintain strict sanitation to avoid microbial contamination, another potential source of VDKs.

Conducting an Attenuation Limit Test

Want to optimize your wort fermentability? Try this:

1. Fill a sanitized 750 ml flask with wort.
2. Overpitch with a generous amount of yeast.
3. Cover, shake well, and keep at room temperature (68°F/20°C).
4. Check gravity daily, shaking or stirring as needed.
5. When gravity remains stable for 48 hours, you’ve reached the attenuation limit.

This test helps you fine-tune your mash process for better control over residual sugars and final alcohol content.

Bottom Line: Proactive Diacetyl Management 

For American brewers, proactive VDK management especially with ALDC enzyme ensures clean, hop-forward beers without unwanted buttery notes. By combining enzyme technology, careful dry hopping, and robust quality control, you can consistently deliver the beer flavors your customers love.

Looking for expert advice or the right ALDC product for your brewery? Contact our Technical Team on sales.us@murphyandson.com we’re here to help you craft your best beer yet.

Written by Eric Drost, Murphy & Son Technical Manager