Droopy, I had not made this wine when I posted the recipe four years ago, but have since then. It is indeed a thinner wine than most, but also a sweet wine and sugar adds a little body to it. You can add a little glycerin to it to help thicken it a bit, but I would not over-do it. One tablespoon per gallon should be plenty. I would not add grape concentrate to this (or oak leaf wine) unless you really want to make a different wine.
My walnut leaf wine was not very good until it had aged about 16 months -- 10 months longer than the recipe suggests. It was quite nice at that point, and no thinner than most Japanese Sake. It is not a wine for everyone (but neither is sand burr nor bramble tips nor acorn wines), but worth making for the variety. Make it and cellar it for 16-18 months. I don't think you will enjoy it all that much before then.
As for the sugar, demerara is getting hard to find. I only know two stores in San Antonio, a city of over a million folks, that still carry it. Turbinado and "Sugar in the Raw" are much easier to find and could substitute, but neither has quite the same taste as demerara. Indeed, I think demerara is unmatched in flavor. I just wish it wasn't so expensive and was more available. But, if you have to substitute, I'd go for one of the others (NOT brown sugar, or white sugar with molasses).
Good luck....
Jack Keller, The Winemaking Home Page
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