Wine Making
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,
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,