Controlling diacetyl with ALDC and yeast selection

ALDC (alpha-acetolactate decarboxylase) is an enzyme that breaks down alpha-acetolactate, the precursor for diacetyl within the yeast cell and converts it into acetoin, a flavorless compound. You may be familiar with ALDC, as many brewers use it at the start of fermentation to help avoid the formation of diacetyl, which saves on tank time. However, ALDC is very pH-sensitive and can be less effective as the pH level drops during fermentation (typically below 5), meaning that it might not be super helpful in the case of hop creep. ALDC is a proactive, rather than reactive, solution; it won’t help you clean up diacetyl once it’s already in the beer.

Why use ALDC strains as opposed to adding the enzyme? Some brewers may see cellular-level ALDC as ​“lazy” brewing, but we see it as a time- and cost-saving innovation. Even with great yeast management, having ALDC expressed in the cell increases efficiency in the brewery by reducing tank time. Without the need for a lengthy diacetyl rest, your beer can be turned around faster and with more confidence that diacetyl will be far less likely to form after packaging. Plus, breweries can save additional costs by not buying exogenous ALDC for strains that are not diacetyl prone. 

Should every strain receive the ALDC treatment? In short, no. Some strains are less prone to hop creep-induced diacetyl formation, like British V (OYL-011). However, a handful of strains have exhibited an increased presence of diacetyl in their fermentations and are better candidates for this modification. Again, diacetyl can be avoided and kept to a bare minimum with healthy yeast and properly managed fermentation, but by including this ALDC activity at a cellular level brewers can have more predictable outcomes and save time on troubleshooting and problem solving. 

Is diacetyl EVER okay? Here’s the thing: diacetyl can be pretty controversial! Some brewers have an incredibly low tolerance for diacetyl, going to great pains to remove every possible trace of it from their beer. Others don’t mind it so much, and may even prefer a touch of it in certain styles. Some traditional Czech lagers and English ales will have a low level of diacetyl, such that most drinkers wouldn’t necessarily consider the beers to be buttery, but having a pleasantly round mouthfeel and a hint of sweetness. Brewing these styles with zero tolerance for diacetyl would effectively change their flavor profiles and make them taste different from the classics. 

Sometimes the presence of diacetyl can indicate bigger issues. Apart from stressed yeast or mismanaged fermentation, bacterial contamination is often another source of diacetyl. This can occur in the brewery when equipment like hoses, clamps, and even kegs are not being sanitized properly. Draft lines are another tight spot where bacteria like Pediococcus can really thrive. As a brewer, there isn’t often much you can do about draft line cleaning (unless it’s in your own taproom), but you can equip yourself with the knowledge that regularly cleaned draft lines (biweekly with a caustic solution and quarterly with an acid solution) keep your beer flowing and tasting great.