Contents

Introduction:
The production of wine relies heavily on the microscopic fungus, yeast. With the presence of yeast the sugar found in grapes, the main component in wine, turns into alcohol and carbon dioxide. These sugars are glucose and fructose; the riper and the more sugar a grape contains the more alcohol is produced. The chemical composition of wine is about 70-90% water, 8-20% ethanol, 0.1-20% sugars, 1% carboxylic acid, 0.3% base, 0.2% tannins, and traces of esters, aldehydes, amino acids, cations, anions, polyols and vitamins. Knowing this information is essential for the reaction that is occurring in this experiment. For the purpose of this assignment the investigation is focusing on Sauvignon Blanc. It is recommended Sauvignon blanc is stored in a chilled place at around 5 degrees which is said to triple the shelf-life of the wine, though once open this does not apply due to oxidation. Sauvignon Blanc is a type of wine which is named after the grape it is produced from. These grapes are easy to grow and are able to display different flavours depending on where it is planted (Figure 1). This is because Sauvignon Blanc relies on the climate and soil to determine its flavour. It has also been confirmed that with the right harvesting and vinification techniques1 climate does not affect whether the wine produced is at a good quality standard. However, climate still plays a predominant role with the end product of wine. The climate affects the acidity of the wine and though this does not directly affect the taste being good or bad, it does however, effect the life of the wine. The main acids found in wine include: tartaric acid, potassium hydrogen tartrate (cream of tartar), malic acid and potassium hydrogen malate. Tartaric acid and potassium hydrogen tartrate are the predominant acids found in wine. These acids are derived from the basic acid form tartaric and malic acids the concentration of each depend on the grape and where the grape was grown. These acids are also organic acids which are broken up into carboxylic acid group (-COOH), this contains carboxyl group (C=O) and a hydroxyl group (-OH) (Deb Smith, 2006). In warmer regions, tartaric and malic acids are lost through the respiration process of fermentation. This is because the respiration process is dependent on temperature. With this lost the end product is typically less acidic than wines found in cooler regions. Because it is less acidic the pH becomes higher and this causes oxidation to increase. This is represented in the table below (Figure 2) which expresses the effects of pH on the oxidation and colour of the wine.

Background:
To have an understanding of this loss of acids, an understanding of the fermentation process is needed. This process is called alcohol fermentation or ethanol fermentation which is the conversion of sugar to alcohol. This process is represented by the chemical equation below (Figure 3):
This equation represents glucose (C6H12O6) converted into ethanol (2C2H5OH) and carbon dioxide (CO2). The chemical equation (Figure 3) has been balanced. Alcohol fermentation is similar to glycolysis which occurs within the muscles of mammals to produce lactic acid. This is represented in Figure 4 (The University of Minnesota, 2012), where it shows the similarities between the two processes. The only difference between the two is alcohol fermentation uses two enzymes to convert the pyruvic acid to ethanol and carbon dioxide while glycolysis only requires one for the production of lactic acid.
These two enzymes, pyruvate decarboxylase and alcoholic dehydrogenase, convert pyruvic acid into carbon dioxide and ethanol in alcoholic fermentation. This transformation is shown in the diagram below (Figure 5) this is showing only the two final steps in alcohol fermentation. Firstly, Pyruvate2 reacts with Pyruvate Decarboxylase during the anaerobic stage of fermentation and produces the CO2 in the final product of