Finding Ideal SO2 Levels
Steve Wise — Pleasanton, California asks,
After reading a good deal of literature (including your book, The Winemaker’s Answer Book) there seems to be a plethora of opinions regarding the amount of SO2 required at different stages and varying pH levels. I find much consistency with the “general” rules for maintaining adequate levels of SO2, but when searching for more specific information, I find that there is a wider range of thought that doesn’t necessarily coalesce. For example, in one book the author suggests that free SO2 levels should never exceed 50 ppm unless “you are trying to address some specific problem.” In a different book, the author provides a table showing the relationship between pH and required free SO2 levels (the higher the pH, the higher free SO2 required). For example, a wine with a pH of 3.7 would require free SO2 levels of 63 ppm, clearly above the first recommendation of 50 ppm. And, in several books, there is a recommendation to reduce free SO2 levels at bottling to 25–30 ppm, with no mention of adjustments for wines with a higher pH.
In trying to simplify matters, I researched the use of molecular SO2 measurements in lieu of free SO2 levels. If I understand correctly, molecular SO2 takes the wine’s pH into account, so any pH scaling requirements are already accounted for in a molecular SO2 target. Most books recommend 0.8 ppm for the proper SO2 level, but don’t mention reducing levels at bottling. Others recommend 0.5 ppm molecular SO2 for red wines and 0.8 ppm for whites. While reading the latest issue of WineMaker, I noted that the Syrah recipe called for bringing the molecular SO2 level to 0.8 ppm (the white wine level) and maintaining it through bottling. While I’m aware that different opinions are more often in play than not, the lack of clarity is giving me a major headache. At this point, my best option for red wines seems to be maintaining a post-MLF molecular SO2 level of 0.5 ppm through bottling. Can you help me understand?