Wine Chemistry

Wine Chemistry
The Importance of Chemical Understanding in Wine Manufacture
An explanation of the chemical processes involved in the production of wine and in those that determine the appearance, flavour and aroma of different wines.
Wine-making is essentially a chemical process. It involves a chemical reaction in which sugars are turned to alcohol and carbon dioxide in the presence of yeast. There are also many other chemical processes going on which affect the strength, appearance, colour and taste of the wine.

Grape Ingredients
Wine is made from grapes. In addition to water, grapes contain two different sugars: glucose and fructose, tartaric acid, malic acid, amino acids and a few other chemicals. The chemical processes of wine-making involve several of these components and the amount of each is important in determining the character of the wine produced.

Glucose to Ethanol
The most important chemical reaction in the wine making process is the breaking down of glucose by yeast, forming ethanol and carbon dioxide as gas. There are various important factors at this stage which affect the wine. First, sulphur dioxide gas is passed through the crushed grapes to kill off wild yeasts. If this was not done the yeasts would compete with one another and fermentation would stop prematurely.

Controlling pH
Next the pH (acidity) of the grape pulp needs to be controlled. If grapes are too sweet, then their pH is too high (acidity too low) then less flavours are produced in the wine. The pH can be lowered by adding tartaric acid at the start of the fermentation process.

Temperature
Finally the temperature must be controlled throughout the process. Fermentation is an exothermic process (heat is produced by the reaction), but there are various reasons for keeping the temperature as low as possible. Yeast stops growing as temperatures increase and will die at higher temperatures. Also at lower temperatures colours and flavours are extracted from the skins and by-products such as esters and aromatic compounds are produced which add to the flavour and also the clarity of the wine.

Advances in Wine Chemistry
As more and more research is done into the constituents of the wine and the way they are formed, two areas in particular stand out. First is the idea that regular consumption of wine in moderation is good for you. Statistical studies have shown that wine drinkers are less prone to heart disease, cancer and other diseases. This may be explained by the fact that wine drinkers tend to have a healthier lifestyle and are in groups which are less at risk to these diseases. It may be that there are certain chemicals that combat certain conditions, for example the antioxidant resveratrol which may reduce cholesterol and the risk of Alzheimer’s disease. These chemicals can, of course, be found in other food and drink without the damaging presence of alcohol.

Improving Wine Making
Then there is the development of the scientific study of the process of wine making, and the technology to improve it. There are many who would desire to depend on the natural processes of grapes and fermentation. Others have studied the chemicals which make up wine, seeking to determine those that cause the flavour, aroma and appearance of wine so that these can be manipulated in the production process. This tension will continue as the desire to make money affects the love of natural processes.

Wine chemistry explains the flavor, balance, color, stability that was once only possible through subjective description. Understanding the principles of wine chemistry will open your eyes to a new level of wine appreciation.