Examination Of Interactions Between Saccharomyces And Brettanomyces Yeasts In Primary Fermentation Of Beer

Open Access
Author:
Cochrane, Katherine Frances
Area of Honors:
Forensic Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Ryan John Elias, Thesis Supervisor
  • John Neil Coupland, Honors Advisor
Keywords:
  • beer
  • 4-ethylphenol
  • 4-ethylguaiacol
  • brettanomyces
Abstract:
This study was conducted to evaluate the different methods of pitching mixed Saccharomyces cervisiae and Brettanomyces bruxellensis yeast cultures into simple un-hopped wort with the objective to find whether the order of inoculation significantly affected the production of volatile compounds in beer. Treatments regarding pitching of yeast were selected to control for single S. cervisiae and B. bruxellensis fermentations as well as mixed culture fermentations: one treatment undergoing simultaneous inoculation of both strains, one treatment undergoing a single B. bruxellensis inoculation and allowed to ferment for 96 hours before undergoing a second inoculation of S. cervisiae, while yet a third underwent initial inoculation with S. cervisiae and subsequent inoculation at 96 hours of B. bruxellensis. Worts into which the yeasts were pitched were made from dry malt extract (DME) and reached an initial specific gravity of 1.055 (12.5°P). Daily time points throughout the fermentation were run through GC/MS to determine relative amounts of 4-ethylphenol and 4-ethylguaiacol, two compounds that are accepted as being indicative of Brettanomyes fermentation. At the end of the fermentation trials, sensory panelists looked at each of the treatments characteristic of “Brett flavor” including vinegar, tropical fruit, spice, horse or barnyard, and Band-Aid® or medicinal aromas and flavors. The results of this study gave evidence that the order of pitching of yeasts may contribute to overall chemical and sensory differences, particularly an increase in positive Brett flavors.