Before you begin your first batch of wine, it is a good idea to understand something of the background of wine and the basics of winemaking. Today there are certainly many kits which can be purchased which will walk you step by step through the process of winemaking. Even so, you may find that you enjoy and appreciate the results all the more for understanding the background of each step.
Wine is produced by fermenting grapes that have been freshly harvested. While many people today have taken up an interest in winemaking, the actual process of making wine has remained relatively unchanged over the years.
As we all know, yeast is essential to the fermentation process as part of making wine. Yeast actually grows on grape skins and then begins to automatically ferment the grape juice as the grapes are crushed. This begins the process of turning the grapes into wine. The combination of grape skins and grape juice is known as the must. When the mixture is in this phase of immersion it is known as maceration. This is one of the most important stages of winemaking, especially when making red wines. The actual color of red wine is obtained not from the juice inside the grapes but from the color of the grape skins. The juice inside all grapes, regardless of the skin color of the grape, is actually clear. In order for red wines to obtain their dark color they must extract the color from the skin of the grape. This is why black grapes are commonly used for the production of red wines. Conversely, light colored grapes are used for the production of white wines.
During the actual fermentation process, the natural fruit sugar that is contained within the grapes undergoes a conversion process into equal parts of carbon dioxide and alcohol. As this process continues, heat is released. It is for this reason that stainless steel fermenters that can be temperature controlled are commonly used for the production of rather delicate white wines. This prevents the wine from ‘cooking.’
The ripeness of the grapes and the sugar content contributes to the level of alcohol that is produced during the fermentation process. The time at which the fermentation process is stopped can also contribute to the alcohol level as well.
The dusty look of grapes, frequently referred to as their bloom, is produced by yeasts. The skins of grapes contain what is known as vinegar bacteria. Once exposed to air, vinegar bacteria can spoil new wine quite quickly. As a result, it is necessary to eliminate wild yeasts in order to avoid ruining the taste and the aroma of the wine. Winemakers use a centuries old process of utilizing sulfur dioxide to kill the vinegar bacteria as well as slow the growth of other bacteria and molds in the wine. Sulfites can also help to cease the browning or oxidation of wine as well as preserve its flavor.
Generally, the amount of sulfur dioxide that is used in the winemaking process is quite small. Typically, only between 60 and 125 parts per million are used. It is important to understand that even if no sulfur dioxide is added to the wine, there will still be some sulfites present in the wine due to the fact that they will be produced from fermenting yeasts. This is why all wines that are purchased in the United States contain the label “Contains Sulfites” on the bottle.