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How do winemakers know what the alcohol content will be in wine?

On a recent tour, a lovely guest named Mason asked me an interesting question. The question was “how do they know what the alcohol content will be in the wine?”

The answer

The amount of sugar in the grape when it is picked determines how much potential alcohol in the finished wine. When all the sugars have been converted to alcohol through fermentation, the wine is said to have been ‘fermented dry’. Thus, a dry wine has no residual sugar.

Grapes almost ready to be harvested

Key points

  • Sugar ferments into alcohol: the amount of sugar in a grape will equate to how much alcohol is in the wine
  • Baumé: is the fancy French name for the measure of sugar in the grape
  • Grapes are measured for sugar in the vineyard: Both by taste from the winemaker and by scientific instruments like refractomers
  • The riper the fruit is the more sugar there will be: Like fruit in a fruit bowl, grapes will get sweeter and more ripe and eventually start to rot
  • The amount of sugar in a wine is one of the key indicators of when to harvest: When time to harvest, winemakers will be measuring regularly and when the sugar level is right, they will pick the bunches

The amount of sugar in the wine will have an effect on other elements of the wine too. For example a Pinot Gris which has more fruit and body is picked later than a Pinot Grigio which is lighter and more acidic (more on that in our “What’s the difference between Pinot Gris and Pinot Grigio?” article)

Fermenting red grapes at Giant Steps

A few extra points:

  • Some yeasts are better than others. There is a standard and most efficient yeast for wine fermentation, which will always produce a predictable result, with total dry fermentation
  • Fermentation can be stopped early by adding sulphur, or changing the temperature. This will result in a lower final alcohol and greater residual sugar – a common method for making sweeter styles and dessert wines.
  • Fermenting sugar produces carbon dioxide as well as alcohol. Retaining carbon dioxide is key to making Champagne and other sparkling wines – but I’ll save that for another blog post.

Some other interesting articles about wine include:

What are Tannins in Wine?

What is the difference between red wine and white wine?


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