Date of Award

8-2016

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Food Science and Human Nutrition

Advisor

Jason Bolton

Second Committee Member

L. Brian Perkins

Third Committee Member

Lawrence Leblanc

Abstract

Using novel approaches, several methods were developed to expand the breadth of knowledge for beers that are being brewed with Brettanomyces yeasts. Cell counting is traditionally preformed with a bright field microscope and methylene blue dye for viability. Using a Cellometer, we designed a method to digitally and rapidly count the yeast ceils and determine viability in propagations and fermentations. This is a great improvement over traditional methods as the fluorescent dye capabilities of the Cellometer allows the user to differentiate between individual cell nuceli within pseudohyphae cell morphology leading to more accurate cell enumeration.

Organic acids, specifically lactic and acetic acid, have a significant impact on the flavor of beers that are brewed with Brettanomyces. Acetic acid is metabolized by Brettanomyces species in the presence of oxygen while lactic acid is formed by lactic acid bacteria, which are common co-fermenters for American sour beers. High pressure liquid chromatography and ultra-high pressure liquid chromatography method were developed to quantify the concentration of acetic and lactic acid in beer. These methods were then compared to the traditional method of titratable acidity and the benefits and drawbacks of each method were examined.

An ultra-high pressure liquid chromatography method for carbohydrate was developed, as a way to monitor sugar consumption during the fermentation process. This method utilized an evaporative light scattering detector.

A final study using all the methods designed for this project examined different aeration rates effect on the final concentration of organic acids, how cell density changes over time, and the rate at which sugars are consumed by Brettanomyces yeast.

These experiments were all designed to help shed light on the impact of brewing techniques on the final beer product when the only yeast strain utilized in fermentation is Brettanomyces. In addition, we hoped to create applications that can be used in the brewing industry to help brewers create the most consistent products possible.

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