Killer Toxins for the Control of Diastatic Yeasts in Brewing

Secondary fermentation in craft beers by diastatic yeasts can result in undesirable consequences, such as off-flavors, increased alcohol content, gushing, and the explosion of packaging. Currently, there are no strategies for inhibiting diastatic yeasts once they have invaded a commercial brewing process. Many strains of yeasts can naturally produce "killer" toxins that inhibit the growth of competing yeasts. Testing the effectiveness of canonical toxins against diastatic yeasts revealed that most (90%) strains are susceptible to the K1 killer toxin. Only two diastatic strains resistance to killer toxins was due to toxin production and associated immunity. Four diastatic strains resistant to K1 and K2 toxins were screened against a library of 192 novel killer yeasts to discover novel antifungal activities. This identified novel K2 killer yeasts that were more potent at inhibiting diastatic yeasts than the canonical killer yeast. As proof-of-principle for the control of diastatic yeasts during fermentation, killer yeasts were found to be effective at inhibiting hyperattenuation after a simulated diastatic contamination in a 1,000-liter industrial-style fermentation.