The fermenting process in wine creates the alcohol but how is it made to be a certain percentage?

Question

The fermenting process in wine creates the alcohol but how is it made to be a certain percentage?

Answer 1

Different strains of yeast can survive at different levels of alcohol.  Since the yeast is fermenting sugars into alcohol, it is basically creating an environment where it can not survive.  If you have a hardy yeast, it will survive longer, turning more sugar into alcohol.

Examples:

YEAST STRAIN: 1214  |  Belgian Ale - 9%

YEAST STRAIN: 3463  |  Forbidden Fruit - 12%

YEAST STRAIN: 4946  |  Zinfandel - 18%

Answer 2

The thing that causes fermentation is the yeast.  Most yeast can survive up to about 11% alcohol ,beyond that they die off.  Some special "Yeasts", can push it to about 13% in a very controlled environment.  Port Wine (fortified) has had alcohol added to push up the percentage.

Answer 3

so, not sure where some of the other answerers get their information.  Here's fermentation 101.  The basic equation, as you already know, is yeast eats sugar, produces alcohol and CO2.  The process stops when the yeast has consumed all the sugars or the alcohol reaches about 15%.  At about 15%, the yeast dies.  To your great question of how level of alcohol percentage is achieve, you need to turn to the winemaker.  

Winemakers know what wine they want to produce long before the harvest, and that includes alcohol content.  So, as the grapes ripen, winemakers will constantly measure sugar levels in the grapes and pick when it has enough sugar for the wine they want to create.  High alcohol wines means picking as late as possible to allow the grapes to get the most sugar possible.  The trade off, of course, is less acidity.  (picking early to preserve acidity/freshness and adding sugar during fermentation to boost alcohol levels is a whole other book to be covered elsewhere).

Other ways winemakers determine the alcohol content is to monitor the fermentation process and stop it when the wine has the balance of sweetness and alcohol they want.  A way is to fermentation at cold temperatures and chill to stop fermentation.  Filter out the yeast and add sulfites.

And then, there is the whole late harvest wines, noble rot wines and Eiswein fermentation that adds another footnote to how percentage of alcohol is determined.

The Short Course.

PS White wines can have as high an alcohol content as red  wines, its all a function of sugar content and winemaker intent.

Answer 4

Basically, fermentation is when a microorganism such as yeast or bacteria undergo anaerobic respiration. Under those conditions, they eat sugar and produce CO2 and alcohol as waste. The more they eat, the more waste they produce. Grapes tend to be more sugary than barley, which is why most wines have a higher alcohol content than most beers. The way they test for the alcohol is by using a useful brewing tool called a hydrometer. I have never used a hydrometer, but it has to do with the original gravity and they have a formula that converts the hydrometer reading to % alcohol. They can then add more food for the yeast to tweak it up to the level of alcohol they want, almost the same process as brewing a high abv % beer.

Answer 5

The yeast is on the wine skins. That is why they have to be crushed to make the wine. Pasteurize the juice, and all you have is grape juice.

The alcohol level will increase with the level of sugar in the juice.

White wines don't have as much sugar as the reds do, so the alcohol level is lower.

Answer 6

The percentage will depend on the amount of sugar & the yeast type.