The rhubarb plants on the allotment grow across the path, so when we visit we pull any stalks that are obstructing the way. Last time I went I pulled 15lb of rhubarb (about 7kg. I know - it sounds like a lot to me, too), which is enough to make 5 gallons of rhubarb wine.
The first stage of making any wine is to extract the flavour from the main ingredient. You can squeeze the juice directly from grapes, oranges etc. But some other ingredients need different treatment, often by boiling in water then straining. Rhubarb is a bit unusual - you chop it up then cover with sugar. The sugar sucks the juice out of the rhubarb and dissolves, then you strain off the syrup, dilute it with water and ferment that. I didn't believe it either, but I had a go, and it worked just as it said in the book.