A couple weeks ago I had the privilage of leading a Diacetyl training for the Los Angeles Brewers Guild alongside Jace from Paperback Brewing.  After the training, I thought it would be a good topic to share with you all.  

Introduction: 

Diacetyl, with its distinct buttery aroma and flavor, is a compound that both intrigues and concerns brewers and beer enthusiasts alike. While it can contribute to the complexity of certain beer styles, excessive levels can be off-putting. In this comprehensive guide, we'll explore the detectable range of diacetyl, acceptable levels, styles where it's tolerated, breweries with notable diacetyl issues, its production, management in breweries, post-fermentation elimination, minimization techniques, and testing methods.

Detectable Range and Acceptable Levels: 

The detectable range of diacetyl in beer can vary depending on individual sensory thresholds and testing methods. Generally, concentrations above 0.1 parts per million (ppm) become noticeable to most individuals. Acceptable levels vary between beer styles and consumer preferences, typically ranging from 0 to 0.3 ppm. However, some styles, such as English ales and certain lagers, may tolerate slightly higher levels.

Styles Where Diacetyl is Acceptable: 

Certain beer styles are known for their subtle diacetyl character, which is considered acceptable or even desirable. These include traditional English ales, such as Bitters and ESBs, where low levels of diacetyl can contribute to the beer's perceived maltiness and enhance its overall character.

Brands with High Levels of Diacetyl: 

While most breweries strive to control diacetyl levels within acceptable ranges, some brands have faced criticism for consistently high levels of diacetyl in their beers. However, it's essential to note that diacetyl levels can vary from batch to batch and may be influenced by factors such as brewing techniques, yeast health, and quality control measures.  The brands that we tasted with Diacetyl were Pilsner Urquel and 

Production of Diacetyl: 

Diacetyl is a natural byproduct of fermentation, originating from the precursor alpha-acetolactate. During fermentation, yeast produces alpha-acetolactate, which is then converted to diacetyl. Factors such as yeast strain, fermentation temperature, wort composition, and oxygen exposure influence diacetyl production.

Managing Diacetyl Production in Breweries: 

Breweries employ various strategies to manage diacetyl production, including:

1. Yeast Selection: Choosing yeast strains with low diacetyl-forming capabilities or employing diacetyl-reducing yeast strains.
2. Fermentation Control: Maintaining stable fermentation temperatures and adequate oxygen levels.
3. Quality Ingredients: Using high-quality malt and hops to minimize precursors that contribute to diacetyl formation.

Eliminating Diacetyl Post-Fermentation: 

If diacetyl is detected post-fermentation, breweries can employ techniques such as diacetyl rests, forced diacetyl reduction using fresh yeast or bacteria, or extended conditioning to reduce diacetyl levels.  

Minimizing Diacetyl: 

To minimize diacetyl in the final product, breweries should focus on quality ingredients, rigorous sanitation practices, and robust quality control measures throughout the brewing process.

Testing for Diacetyl: 

Breweries can test for diacetyl using sensory analysis by trained tasters or chemical analysis methods such as gas chromatography, which provides accurate quantification of diacetyl levels. Our brewery employs two methods for testing.  We do a forced diacetyl test and also use our spectrometer. 

Conclusion: 

Diacetyl management is a critical aspect of brewing quality beer. By understanding its detectable range, acceptable levels, production mechanisms, and employing effective management techniques, breweries can ensure that their beers meet consumer expectations and deliver enjoyable drinking experiences. Cheers to crafting exceptional beers, free from unwanted diacetyl issues!