In about two weeks most of the sugar will have been consumed by the yeast and fermentation will slow, making it easier to keep track of the falling sugar level of your wine. You want to be aware of your sugar levels because they will give you an overview of how the ferment has been progressing. You may wish to stop the fermentation early and leave a bit of residual sugar in your wine.
Note: This time frame is dependent on yeast strain selection, the starting ºBrix and fermentation temperatures. Just like people, yeast are more active when they are warm. So, if you are fermenting at 65º F the sugars will drop much sooner that if you are fermenting at 55º F. Each wine's rate of fermentation will be different so you will need to check it throughout the fermentation to monitor the progress.
When is the Fermentation Over?
The fermentation is considered done when you either reach your desired sugar level or go "dry" at 0° Brix. A wine with 0.2% residual sugar contains two grams of sugar in a liter of wine. Dry wines are typically in the 0.2%-0.3% range, off-dry wines in the 1.0%-5.0% range, and sweet dessert wines are normally 5.0%-10%. However this can be a little subjective on taste and a wine with .5% or 5 g/L may taste completely dry depending on the wine. In the end there is no "correct" sugar level for your wine, it just comes down to your personal preference.
Creating a dry wine
Fermenting to dryness simply involves letting the yeast continue the fermentation until all of the sugars have been consumed. If a secondary malolactic fermentation (MLF) is desired, no SO2 is added and ML bacteria are added to the wine (see our Guide to Malolactic Fermentation). If no MLF is desired then the wine is immediately sulfited (with a thorough stirring) and we proceed to the ageing period (see our Guide to Tasting and Adjusting during Ageing).
Creating a wine with residual sugar
Finished wines with residual sugar can be made in one of two ways; by either fermenting to dryness then sweetening at bottling, or stopping fermentation before reaching dryness so that some residual sugar remains in the wine. The techniques for each are as follows:
A word about Potassium Sorbate
Potassium sorbate is used to help stabilize a wine that contains residual sugar. It inhibits yeast reproduction and will stop a renewed fermentation from taking place. However, it will not stop an active fermentation.
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