EVALUATION OF CONSISTENCY AND EXTRACTION KINETICS OF AROMA COMPOUNDS FROM OAK ALTERNATIVE PRODUCTS

Mackenzie Brooke Aragon

Throughout history, oak barrels have been used as a functional vessel. It was only since the 20th century that toasting barrels for flavor and aroma became prominent. As toasting technology has advanced and waste reduction in natural products has been encouraged, additional oak formats for maturation have been developed. These formats are smaller and intended to be immersed in the wine or spirit for which they were being used. Originally these products were a way to use the less favorable or extra oak to prevent waste and provide a less expensive option for winemakers to add oak character to wine. Nowadays, alternative oak formats are made from oak of the same quality as their traditional barrel counterparts. These products have many advantages, including a relative cost reduction, customization of flavor profiles, being more sustainable, and having shorter extraction times. Oak alternatives have been treated with the same anecdotal wine extraction concepts developed from traditional barrel formats. However, due to differences in intended use, concepts regarding toasting methods and extraction have not been critically and scientifically examined from the perspective of a multidimensional object. The work presented evaluates the fundamental concepts underlying assumptions regarding oak alternatives. In Chapter 1, a brief historical review of aging vessels, from the age of amphorae to newer oak alternatives, is included. Species-specific processing techniques for barrels and alternatives are compared. While the number of tyloses may vary and dictate processing methodology, the fundamental polymers are the same. The thermal degradation of lignin, cellulose, hemicellulose, and hydroxy fatty acids is reviewed. As a result of the various pyrolysis reactions, many volatile compounds are released and degraded, with behavior depending on the specific compounds. The degree of toast intensity directly impacts the final volatile composition. A review of the various degradation pathways provides important background information about the development of specific volatile compounds. Before evaluating other parameters, such as the source, seasoning, and grain tightness, consistent toasting must be assessed first. The lot-to-lot consistency of alternatives in medium, medium plus, and heavy toast intensities produced by five commercial producers was evaluated for a range of volatile compounds. Products within toast intensity were then compared using linear discriminant analysis, intraclass correlation coefficients (ICC), and individual ANOVA analysis to determine repeatability between lots and within toast intensity. The results show that repeatability within cooper decreases while the differences between toasting method increases as the toast intensity increases. These findings differ from trends observed during toasting of traditional barrels where the repeatability is reduced as the toast intensity increases. The application of an ICC analysis provides a confidence interval which can be directly compared. Now that the repeatability of the different toasting methods used to produce oak alternative products, greater confidence in the kinetics of volatile extraction evaluation can be had. In Chapter 3, the fundamentals extraction kinetics of oak alternatives were evaluated. Oak alternatives are intended to be submerged within a liquid, therefore direct exposure to both the cross- and end-grain. A multidimensional kinetic model was developed to account for the difference in surface types. Separate model outputs, rate constants and equilibrium concentration, for each grain type are then individually determined. When compared to a single dimensional model the multidimensional model fit the experimental data. The rate constants were then compared to molecular weight, showing a correlation for the end grain and not the cross grain. From this model the equilibrium constant can be used to normalize across several compounds so the percent extracted can be determined based on time. This model can also be used to compare between different formats. This model was developed using one toast intensity and one product, therefor to understand the effect of toast, multiple toast intensities must be evaluated. Following the experimental design used in Chapter 3, the extraction kinetics from three toast intensities were evaluated. The kinetic constants varied based on toast intensities, with each compound demonstrating different trends depending on how they thermally degrade. To evaluate differences in extraction rate between the various sized segments, the rate-limiting step in the diffusional extraction was evaluated. Depending on the size and whether agitation to the system occurs, internal or external become the rate limiting step. Agitation minimizes the formation of a boundary between the surface of the wood and the bulk of the solution. The work presented in the following dissertation is only a sub-section of the projects and experiments conducted during this time. Additional work evaluated how grapes and the subsequent wine is affected by smoke exposure. Many of the pyrolysis reactions observed in toasting oak, also occur during a fire event which makes the reaction chemistry fundamentally similar. Toasting oak is a controlled pyrolysis compared to fire events, creating a model system in which many concepts learned and applied to toasting oak can then be applied to a less predictable system.

EVALUATION OF CONSISTENCY AND EXTRACTION KINETICS OF AROMA COMPOUNDS FROM OAK ALTERNATIVE PRODUCTS

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