If you get the stuff that's traditionally made, you get a vinegar made from a sorghum base (like most Chinese liquor is) that uses a very convoluted "koji"-like starter (qu) made of barley, peas and bran. It's about 3000 years old, the technique, and the best stuff comes from Qingxu or Taiyuan. The terroir around these are unmistakable.

Key things that differentiate it from western traditions of vinegar production include:

1. Solid state fermentation where the fermentation happens in large ceramic jars as a solid mass, not as a liquid.
2. Manual turning. Several times per day the mash is mixed up by hand to control temperature and aerate it. (This is back-breaking labour, so traditional Shanxi vinegar is EXPENSIVE yo! The commercial stuff I mentioned automates this.)
3. Smoking. About half the mash is smoked over a fire after fermentation to give it its characteristic smoky (duh!) flavour and black colour.
4. The vinegar is then extracted and put into enormous clay jars for aging.

The aging process involves putting the jars outside into the elements. In the summer the water evaporates away, concentrating the vinegar and flavour elements. In the winter the water freezes at the top and is scooped out, further concentrating the product. After as little as 3 years, but as many as 12, the vinegar is filtered, bottled and sold. The longer the better, generally.

If this were a commercial vinegar it would then be pasteurized to kill any ongoing growth, but the real stuff, again, is not pasteurized (though it is filtered). This means if you get a bottle of the real stuff, you have a living vinegar whose character will change as your store it. The aging doesn't stop when you get the bottle. Store it properly and it will grow ever more complex and flavourful over time. I've tasted some ten year stuff that was later stored in a friend's home for a further five years. It ... yeah. It was not something I'd ever tasted before.

If you decide to try this out, be very careful with your purchase. Make sure you know the provenance of what you're getting back to the individual farm.