While sulfites can occur naturally, what is meant by the use of sulfites in the making of wine is to ADD sulfites to the wine - popularly with campden tablets (potassium metabisulphite). This occurs at two times in commercial winemaking. The first time is when the grapes are first crushed. The purpose is to kill any organisms that might be on the grapes and juice. The natural amounts present will not do the job. The second time is to stop fermentation when they reach their desired alcohol level. All the yeast is killed and therefore cannot convert more sugar to alcohol. It also kills any organisms that might have again been introduced - most particularly acetobacter bacteria, which makes vinegar.
In my experience, the addition of sulfites is unnecessary if you maintain a sterile work environment. I keep my equipment clean and sterile and I have never had a problem with spoilage. Also, the level of alcohol can be precisely controlled without the use of sulfites via hydrometer measurements and proper yeast selection (though the addition of sugar beforehand could pose a problem for sacramental wine). Also, once the wine is done fermenting, the high alcohol level (10-18%/vol) will prevent most organisms from being able to thrive.
There are a host of other additives that can be added (most of this science having been advanced in the past 150 years) to create a more balanced wine. None of these are super critical for making wine from grapes (though I assert that pectic enzymes are critical for a good apple wine, but that won’t be used for sacramental wine - I hope :p).
Then there is the addition of yeast. If someone asserts that the addition of yeast is a violation of no additives, that someone needs a course in chemistry or biology 101. No yeast, no alcohol, it’s as simple as that. Now on the old European estates that have been established for hundreds of years, the addition of yeast is not necessary because they have developed a monoculture in their environment. But most of us need to help nature along and give the yeast the advantage over competing organisms.
Also, the use of wooden barrels could pose a problem for sacramental wine, since that introduces a host of additives that help age the wine. Therefore, today the best option are glass carboys to store the wine.
And due to the fact that it isn’t being aged in wood, the wine should be drunk fairly soon (it won’t get much of an advantage from aging in glass). Sacramental wine is best within a year or two of making.
Did I leave anything out? If you have anymore questions on making sacramental wine or wine in general (grape or other), let me know.