The spoilage of microbrewery beer from Bacillus species isolated from pelletized hops

Microbiology Session
Nathan T Traw, Mother's Brewing Company, Springfield, MO, USA

ABSTRACT: The food and beverage industries are affected by the growing population of microbes that are resistant to current anti-microbial chemicals. Specifically, the brewing industry is seeing the emergence of new beer spoiling organisms that were previously not a concern. Bacillus species are used as an organic pesticide in the United States by hop growers. This experiment seeks to correlate the spoilage of microbrewery beer by Bacillus species and its use as an organic pesticide by the hop industry. Spoiled beer from a recently opened microbrewery was plated on Schwarz differential agar (SDA). Bacillus was isolated and confirmed by traditional microbiology methods that included Gram staining, endospore staining, and enzyme tests. The microbrewery’s hops were then analyzed. Hops were supplied by the microbrewery and were commercial pelletized hops purchased from a brewer’s supply store. The hops were in a vacuum sealed bag and pelletized. The hops used by this particular microbrewery were not purchased as organic. Hops were aseptically sampled and placed in sterile nutrient broth. After 24 hr of incubation, 400 µL of the nutrient broth was plated on SDA. Bacillus was confirmed by traditional microbiology methods as the sole isolate from the hops. The Bacillus culture isolated from the hop sample was then incubated in microbrewery beer. After 48 hr of incubation, the beer was observed microscopically for Bacillus. The presence of live Bacillus cells was confirmed. This confirms that a beer-resistant strain of Bacillus introduced by commercially prepared hops is capable of spoiling microbrewery beer by unknown mechanisms. Future studies on this topic include beer stability, dissolved oxygen concentrations, and genetic sequencing.

Nathan Traw received his B.S. degree in biology-microbiology and biotechnology from Missouri State University in May 2011. During his time at MSU, Nathan spent nearly two years as a student researcher studying the transcription of genes in macrophages in response to bacterial stimuli. Nathan is now the quality assurance and control lead for Mother’s Brewing Company in Springfield, MO. He is currently preparing for the 2012 IBD Diploma in Brewing examinations.