After the primary and secondary fermentations are complete, it’s time to protect the wine. Typically, this means an appropriate level of Free Sulfite is added to the wine to control microbiological contamination. Plus, the wine is moved to a temperature and humidity controlled area and finally, testing & tasting the wine and topping the wine storage container are done on at least a monthly basis.
Sulfite Addition
We added Saccharomyces cerevisiae (yeast) for the primary fermentation and Oenococcus oeni (lactic acid bacteria) for the conversion of malic acid to lactic acid depending on our wine style goals. During this process, there are millions of microorganisms per milliliter working to complete the fermentations. When almost all of the sugar has been converted to alcohol and the malic acid is converted to lactic acid, the wine is considered double bone dry and there’s now a smaller probability for an unwanted fermentation to take place in the bottle later. However, the wine is not protected against other troublesome microorganisms and that’s where the addition of Sulfite helps protect the wine.
One example of an unwanted microorganism, Acetobacter or acetic acid bacteria have the ability to convert alcohol to acetic acid (Vinegar) when oxygen is available. Luckily, Acetobacter are controlled by sufficient Free Sulfite levels while minimizing the exposure to oxygen as much as possible. I’ve attached a link below to a Wine Business site which provides many useful calculators for determining the amount of Sulfite to add. Please contact me with any questions on how to use the calculators.
https://www.winebusiness.com/calculator/winemaking/section/2/
Storage Conditions
Microorganisms reproduce and grow exponentially in ideal conditions but can survive in less than ideal environments. The wine with its high alcohol content and relatively low pH establish less than ideal conditions for many microorganisms; however, as discussed above, Acetobacter is an example of one organism which thrives in wine even with a low pH and high alcohol content; therefore, the wine is stored in a cool environment to help control growth and also to limit the oxidation rate of the wine. From a literature search, the ideal temperature range for wine aging is 52o– 60o F with many wineries storing wine around 55oF. Another very important consideration, many microorganisms are aerobes and require oxygen for life or growth, highlighting the need to limit the wine’s exposure to oxygen during storage or racking.
Humidity is another parameter to control during wine storage. The ideal relative humidity range for wine storage is 55-75%. Within this range, corks won’t dry out too fast and the amount of topping wine added to an Oak barrel won’t be too much each month due to a high evaporation rate out of the barrel. My data with topping wine additions to Oak barrels suggest addition rates are 500 – 800ml per month when stored in a New French Oak barrel.
In summary, it’s no time to relax after the wine has completed fermentation. Proper Sulfite levels, protection from oxygen exposure, temperature/humidity control, and keeping the wine container topped with wine are all vital to produce a quality wine.
