I never thought about that before, that wine kills the mother. It makes a lot of sense though. And, I've poured cider vinegar into half bottles of wine from time to time, and then waited a while before I used it as vinegar. I have no idea whether or not any additional acetic acid was formed.
Here is the thing, vinegar comes to us through two different processes. The one with the mother in a solution that contains sugar of one kind or another, the bacteria or yeast, which ever it is eats the sugar and makes acid and there you have vinegar. Consider
apple cider vinegar. You start with apple juice and when the process is finished, it isn't sweet, it's sour. All the vitamins and minerals from the apple juice, the anti oxidants, what ever is in the juice is in the vinegar. Yum. You can make vinegar out of
honey by diluting the honey with water, adding unpasteurized cider vinegar with the mother in it, waiting.
It is important to let the process have plenty of air. You can't stopper the bottle, and it is good if there is a large surface area where air touches the soon-to-be vinegar liquid.
There are plenty of creatures floating in the air that do NOT make vinegar, so a lot of people like to have guaze or paper of something that lets air through, but not air travelers looking for a place to raise a family. I have used paper held onto the jar with a rubber band. I'm sure plenty of things work.
The other way vinegar is made, white vinegar, is starting with ethanol, bubbling oxygen through it and it oxygenates the ethanol, and you get acetic acid, which they then dilute to 5-8% acid.
In the interest of accuracy, I've checked Wiki, and I'm disagreeing with them a bit. Maybe I'm wrong, but, they do say pure ethanol is "fermented" to make white vinegar, and I'm pretty sure NOTHING grows in pure alcohol, so who knows.
To get rhubarb vinegar, you could either put some rhubarb into a bottle of unflavored vinegar , or you could cook rhubarb with sugar strain, dilute, add live vinegar and wait.
Interesting idea though, rhubarb vinegar.
Thekla