The use of high and low levels of sulphur dioxide, my opinion:
Sulphur is an organic element, naturally created with a key role in the growing of grapes and in the making of wine. The primary purpose of sulphur dioxide addition is to prevent something going wrong in the life of wine. This is based around a desire to keep oxygen away from the wine, because without this use it can oxidize components in the wine, create reduction in fresh aroma, change in colour but can also encourage the growth of spoilage bacteria such as the various lactic acid bacteria and others, as well as wild yeast that can grow in wine and turn into stinky compounds. The effects of sulphur dioxide can be grouped into four categories: antioxidant, stabilizer, solvent and modifier of taste. In must and wine, there are several substances that tend to oxidize, changing both the look and the taste.
There are different benefits related to postfermentation. One can be the style of wine that the winemaker wishes to create; for example the adding of sulphur dioxide after the postfermentation destroys or blocks the development of bacteria responsible for malolactic fermentation (generally avoided in white wines) in order to avoid it and to keep the natural acidity of the wine. In this case the level of sulphur needs to be higher, if the purpose is to undergo malolactic fermentation the use of SO2 becomes lower. Sulphur dioxide also plays a positive effect on the taste and aromas of the wine, to eliminate and reduce the tastes of rot and mould. To obtain these positive effects, sulphur dioxide must be added when the alcoholic fermentation is finished completely. The level of pH is an important role of using SO2 to provide adequate protection from microbes and oxidation. A lower pH solution will require less sulphur dioxide in order to maintain the proper level molecular SO2. Since the conservation of wine is always a critical factor, a wine properly stored will always have a certain amount of free sulphur dioxide and that's sometimes a factor in the decision of whether to use a high or low level of sulphur dioxide. An important time for the addition of SO2 is when you do racking and that's to avoid oxidation to maintain the correct use of the oak or the container you choose for aging the wine. In this case the level of sulphur can be determined in the quantity to apply, the higher - the wine is less exposed to oxygen and avoid the possibility to have more sediment in the wine. The adding of SO2 removes as much of the sediment as possible, so the process of clarification is further a goal. However with a high level of sulphur you are going to lose the integrity of the wine, such a bouquet and tipicity of grape varieties; thus the less you use you are going to respect the concept of terroir even if in the final bottling there is a small amount of sediment in the wine. Once again, if there is malolactic ferment involved and/or you are going to do bottle ferment later, for example in regards to champagne, you want to keep the SO2 down. Since under these conditions, the pH is going to be low, you are probably okay adding a very low sulphur dioxide. In sweet wine making, the level of sulphur dioxide added is normally the highest and also in postfermentation, dessert wine contains a lot of sugar, and active free sulphur will combine with this sugar. So a Winemaker will have to keep adding more free sulphur until the wines natural sugar and oxygen have been used up. It needs to reach saturation point, then the additional free sulphur will remain free and be able to protect the wine. Therefore the total sulphur content of the end wine will be very high. Reasonable if the grapes are in perfect shape and the pH is low enough this can help even in postfermentation to do less with the addition of sulphur dioxide; you are going to work with a good product and the intervention can be very minimal.
The alternatives of sulphur dioxide are in experimentation in the study of process of winemaking, since from the first commercial of wine from the English and Dutch to help to preserve their wines during transport. The barrels before filling with wine, sulfur candies were burnt inside to protect the wine. It was a trick that they learnt from the Romans who conducted the same practice over millennia before. However a study to try to replace the use of sulphur dioxide has shown a possible alternative especially in postfermentation can be the use of lysozyme which is a protein derived from egg whites it can help to delay or block the malolactic fermentation, prevent unwanted bacterial growth during storage or ageing and inhibit further bacterial spoilage in the case of stuck fermentation. Since sanitation play a critical role in winemaking, like cleaning barrel and tank to kill undesirable spectrum bacteria, fungus, moulds and yeast which can affect the wine especially in postfermentation; the use of Ozone an organic sanitizer, helps to clean and sterilize the environment and containers where the wine aging and give perhaps the possibility to avoid the use of SO2 in the winemaking. Although sulphur dioxide is free produce in small amount by wine yeast during alcoholic fermentation, thus to avoid the use of Sulphur dioxide the fermentation in maceration with the skin needs to be as long as possible to allow the yeast with the help of anthocyanins and polyphenol to protect the wine.
To my point of view exceptional healthy grapes require less intervention of treatment, for example aging the wine on the lees, left at the bottom of the oak protect the wine from oxidation, act as a stabilizer and preservative for the wine; which in this way become naturally elegant. The wine must be accompanied by frequent tasting to monitor the integrity and maturity in order to decide the time of bottling. At this point you decant the wine, assemble the various barrels and proceed to bottling. If you have good body, good value of volatile acidity and low in general other values (pH, residual sugar, dry extract) are in equilibrium with each other, a wine-grower-winemaker, brave, can and should bottle without adding sulphur.