Fermentation is the process of microbes eating sugar, resulting in an acid byproduct, not the other way around.
Actually, there is no real fermentation in tobacco, like we know of in other genres. This is enzymatic. Microbes that develop during the curing stages die away, and the enzymes left behind work on it.
In krauts and when people make real pickles, not the grandma ones where the pour vinegar over them, it is a bacterial infection that occurs that produces acetic acids. I get this when I have used jars in making cavendishes out of my homegrown tobaccos. This wasn't on purpose, just reusing jars to cook the tobaccos, and then aged some in the jars and discovered that the twists that I stored in the jars created an acetic acid.
Most likely, it has to occur on its on, sort of like the natural process that cabbage goes through in becoming kim chi or kraut. Once the storage thing has produced this desired reaction, just don't wash it. I don't think acids have to be introduced artificially.
The old videos that I remember watching from McClellands a long time ago showed concrete surface with someone turning the tobacco with a shovel. My guess is that the slab had developed the bacteria, and they just kept feeding it tobacco... similar to using a starter to keep making sour dough breads. Rough analogy, not exact, but hopefully you get the image of how it might work. This is just logical guessing based on my experiences in playing and processing my own homegrown tobacco experiments, watching videos, and listening to podcasts of Mary and Mike... and filling in the gaps with what makes sense.
Who knows, maybe I'm wrong, but just adding vinegar to tobacco never gave me anything that tasted very good. And, I tried many different varieties of vinegar.