Once the sugar in the bucket of rhubarb has all dissolved - takes about a day - the sugar can be gradually rinsed off with a gallon of water into another bucket.
Keep the rhubarb as it can be cooked down & eaten.
Actually it can be eaten as it is like sweeties - the sugar softens the rhubarb as well as sweetening it.
Add in the tin of grape concentrate and give the bucket a stir.
At this point, the specific gravity of the mixture needs to be taken - pop the hydrometer into the bucket (or a sample jug) & take the reading.
It should be somewhere about 1080 - 1090, although if it is lower than that, more sugar can be added (add by 2oz at a time) until the reading is there or there abouts.
Now for the magic.
Add a teaspoon of yeast nutrient & a teaspoon of yeast, give a final stir, cover the bucket & leave in a warm room. By tomorrow morning it will be fizzing away, turning the sweet rhubarb juice into light fruity delicious wine!