Closing Up The Wine Fermenter Lid After Adding Sulfites
Most wine making recipes instruct the winemaker to add sulfites such as Sodium Bisulfite or Campden Tablets to a starting must. These sulfites are added to the juice 24 hours before adding the wine yeast as a sterilizing process. The sulfites are released into the juice destroying any molds or other contaminants that may be present, wild yeast included. This allows the winemaker to start his fermentation off with a clean slate, so to speak.
Once the sulfur has been added to the juice, it slowly starts to dissipate into the air in the form of a gas and eventually all goes away. This process usually takes between 18 and 24 hours. After the 24 hour waiting period, the winemaker can then safely add fresh, domesticated wine yeast without fear of it being destroyed by the sulfites.
It is important during this 24 hour waiting period that the juice is allowed to breath. That is, to allow the sulfites to escape. The fermentation container should not be sealed up or even fitted with a wine airlock, but rather, it should be covered only with a very thin towel, at best. This is simply to keep foreign matter from getting into the juice.
If the sulfites are not allowed to dissipate into the air during the 24 hour waiting period, then it is highly likely that most of the wine yeast will be destroyed when it is later added to the juice. The result is a fermentation that is very sluggish or one that will not start at all.