Wine Fermentation and its Details
Wine fermentation is a process of transformation sugars present in grapes by yeast under anaerobic condition into alcohol, carbon dioxide and some by-products. Wine is a fermented product and not a distillery product. The alcohol content of wine is 10% to 14 % and the alcohol content of appetizer wine is 14 % to 20%.
“Wine can be defined as a fermented product made by fermentation of a fine quality of ripe grapes and modified by cellular treatment”.
Wine fermentation in fermentation Tanks
There are basically five types of wine
- Appetizer wine
- Red table wine
- White table wine
- Dessert wine
- Sparkling wine
Table showing types of wine, its examples and alcohol content
Here in this article, we will study red table wine in detail.
Red Table Wine
Red table wine is produced from red or black grapes. The alcohol content of red table wine is 10 to 14 %. In the process of winemaking, the grape juice is converted to the alcoholic beverage by a selected strain of yeast. The sugar present in grape juice is converted into ethanol and carbon dioxide. Here in this article, we will be studying Fermentation of Red table wine in detail.
Outline of Red table wine fermentation
In the process of red table wine fermentation, the black or red grapes of proper maturity are selected. These selected grapes are crushed, steamed, and treated with sulphur dioxide. Further, this treated fermentation media is inoculated with a pure culture of yeast. The fermentation is carried out and after the short period of time the drawn off and placed in a storage tank for the further fermentation process. Further, this wine is racked,stored for ageing after ageing the wine is clarified and packed.
Flowchart of Wine fermentation
Details of Red table wine fermentation
Wine fermentation is carried out in following steps
1] Raw Material
The production of best quality of wine requires proper selection of grapes. The grapes of proper maturity and quality are selected. The whole bunch of proper mature grapes is selected. The maturity of grapes is determined by determining the balling degree of grape juice.
2] Stemming and Crushing of grapes
The stemmed grapes are crushed in a clean machine. The machine should be made up of stainless steel, Nickel or Inconel. These metals are oxidation and corrosion resistant and they do not interfere in the fermentation process.
3] Treatment before Fermentation
The juice obtained after crushing and stemming of grapes and the pomace that the stem, skin and seed of grapes contain its surface microflora. So now it is important to remove this microflora and this microflora is removed by treatment of sulphur dioxide gas. This sulfur dioxide gas binds with the surface of micro-organism and kills it and inhibit the growth of unwanted microflora. Before starting the fermentation this is an important step that should be carried out. Another option is pasteurization but if the juice of the grape is treated with pasteurization technique it causes a bad odour from grape juice which can affect the quality of the wine. So here we do not use pasteurization technique.
4] Primary Fermentation of Wine
- Fermentation organism used is Saccharomyces cerevisiae or Saccharomyces ellipsoids. The best strain used is Burgundy and Tokay.
- The fermentation media is sterilized for six hours with sulphur dioxide gas. After sterilization, the fermentation media is checked for it optimum levels of sugar, nutrients, acidity, Carbon and Nitrogen content.
- The fermentation media is added with 2 % to 5 % of inoculum in aseptic condition.
- After addition of inoculum aeration process is started and aeration is very important in wine fermentation because of aerobic micro-organism and its important for the growth of yeast and alcohol production.
- The aeration condition is continued for few hours and then the anaerobic condition is obtained. Once the anaerobic condition develops the pomace starts to float on the surface and this pomace is dumped downwards in media twice. Dumping of pomace is important for the development of colour and tannin.
- The optimum temperature maintained during fermentation is 21.1 ° C to 23.9 ° C.
- The proper development of colour and tannin is observed and fermentation is stopped. Generally, incubation of first fermentation is of 3 to 4 days.
5] Secondary Fermentation of wine
- The primary fermentation is stopped after the development of desired colour and tanning of wine. In secondary fermentation of wine, the wine is drawn off from primary fermentor and filtration of the wine is carried out. This filtered wine is called as fine run wine and now this wine is carried out for further fermentation.
- This wine is stored for 7 to 11 days in fermentation tank at 21.1 ° C to 23.9 ° C in a closed storage tank equipped with bungs. This tanks with bungs help in removal of excess Carbon dioxide.
6] Unusual seller treatment
After removal of excess Carbon dioxide, the wine is drawn off and undergoes to the following steps.
- Racking – The drawn off wine from secondary fermentation tank contains sediments of potassium bitartrate, protein and some particulate matter. So the wine is stored in tanks for one to two months for sedimentation of potassium bitartrate, protein and some particulate matter. Drawing of wine from this sedimented matter is called racking process. This wine is stored at cold temperature because potassium bitartrate settles rapidly at low temperature. Racking process helps in clarification of wine.
- Storing and ageing – Storing of wine in tank is one method of ageing of wine. Storing and ageing of wine causes two major changes in wine that are
a] Clarification of wine
b] Development of flavour in the wine
There is one more method of ageing of wine and that is flash pasteurization. This method of ageing is the fast and quick method. In this method, the wine is held for 71.9° C for 15 seconds as we know protein get coagulated at high temperature. So at this temperature, the protein present in wine is coagulated and after high temperature, the wine is suddenly brought to the low temperature that is – 2.78 ° C to – 4.44 ° C. Here at low-temperature potassium bitartrate get sedimented. Now this coagulated protein and sedimented potassium bitartrate is removed from wine by the filtration process.
3. Clarification – The clarification process is carried out after ageing process. The clarifying agents like gelatin, Casein, bentonite, are used. These agent are suspended on the surface of the tank. The suspended particles in the fermented broth get attach to these agents and settle down. Thus clarification process takes place.
7] Packing of wine
The clarified wine is placed in barrels, cans or bottles for sale. Bottles of small and medium size are pasteurized at 140 ° F/ 63 ° C for 30 minutes.