Overview
This honours thesis modelled compositional changes in bottled Semillon subjected to constant temperatures of 16°C, 25°C, 35°C and 45°C, and a cyclic 16-25°C regime, over 57 days. Radiant heat caused browning, accelerated loss of free and total sulfur dioxide, and detectable sensory differences, all proportional to total heat exposure. Chemometric modelling of ultraviolet-visible spectral data and combined colour/sulfur dioxide data produced valid models of these changes, though mid-infrared spectroscopy data did not. Small 100 mL sample bottles were also found to reliably simulate industry-standard 750 mL bottles. This thesis should be seen as a background knowledge source; a significant amount of research has been conducted since publication, so readers should refer to more recent published research and other Wine Australia resources.
Abstract
Bottled white wine is subject to many environmental influences between production and consumption. Radiant heat exposure is probably the most likely to occur and has the potential to cause chemical and sensory changes to the wine, both of which can have consequences for the wine’s perceived value.
This research project set out to identify whether the chemical changes could be modeled by subjecting a commercial white wine to varying degrees of heat exposure over an extended period of time with analysis of key components at regular intervals carried out using instrumental methods. The instruments used were ultra violet-visible (UV-Vis) and Fourier transform infra red (FT-IR) spectrophotometers and a specific sulfur dioxide auto-analyser used by wine industry. The instruments and methods were chosen as they were able to be replicated in winery laboratories. The UV-Vis was utilized to provide both spectral data and to produce standard colour space values using the CIELab scales.
There was also limited sensory assessment carried out to determine if the treatments had produced significant sensory changes by the end of the storage period.
The results were then processed using chemometrics (specifically the PARAFAC methodology) to identify the key components and produce a model which explains the behavior of the components.
The project found that there were significant differences between the varying levels of radiant heat exposure with wine exposed to higher temperatures appearing markedly different in both chemical and sensory terms.
Using PARAFAC, it was found that valid models of compositional change could be developed using the UV-Vis scans and the CIELab and sulfur dioxide data. It was found that the FT-IR models were unable to produce valid models in this project.
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