Fermentation is the process where the grape juice is joined by other ingredients resulting in a chemical reaction that produces wine.
The formula for the fermentations process is: sugar, added to yeast yields alcohol and carbon dioxide. The yeast, added to the grapes converts the natural sugars contained in the grapes (glucose and fructose) into ethanol and carbon dioxide. The carbon dioxide is then released from the wine mixture into the air and the alcohol remains.
When all of the fruit’s sugars converts over to alcohol or the alcohol is tested and found to be 15%, then this means that fermentation is complete and all the natural yeast as well as the added yeast nutrients has been destroyed. The winemaker then has his goal in sight, he has his wine.
In order to find out if the sugar has been absorbed, the winemaker can use a hydrometer. This apparatus when floated in the mixture will sink to the bottom as an indication that the sugars have been converted and the wine is ready for the next stage.
Red wines do best when, while they are fermenting, they are being stored in an area where the temperature is 70 to 90 degrees. Anything warmer than that will result in your wine essentially being destroyed. The contents inside would basically cook, just like they would if you left a bottle of unopened wine in the hot, desert sun. The cork would dry out, the protection for the wine would be gone and the contents inside would be affected.
Large wineries will ferment their red wine in oaken kegs, and their white wines in large stainless steel vats. Unlike red wine, white wine needs lower temperatures in order to ferment properly. Less than 60 degrees is ideal. Full-bodied table wines can also be stored in barrels. The temperature for fermentation for white wines Fermentation takes place in 55-60 degrees. A vast difference then the hot temperatures needed to age the red wines.
Winemakers will often add more nitrogen and micro nutrients during the fermentation process to prevent any production of hydrogen sulfide gas. If this gas invades the grapes, it imparts a rotten egg smell thus stinking up the mixture. Great care is taken to avoid this chemical reaction, though even the most experienced winemakers can have this unfortunate reaction occur without any fault of their own.
The resulting liquid during fermentation is called the “must.” In order to stop bad bacteria from invading the must, the mixture must be mixed. The must will begin to bubble within 8-20 hours. The first stage of fermentation process for red wines is 5-10 days. White wines sit for 10-15 days. After this time period passes, the second phase of fermentation begins.
During the second phase of fermentation, the wine is siphoned into an airtight container with great care taken to not add anymore oxygen at this point. This second phase process yields in the end, a higher alcohol content. Depending on what ingredient(s) the winemaker adds to this mixture; more yeasts, or perhaps a blended finished wine, will determine if the end result for this harvest. Will it be a sweeter or a stronger wine, and will it fetch a decent price on the market, or with a collector?
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