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BUT FIRST - about sugar:
I guess there's no harm in reminding you that yeast turns sugar into CO2 plus alcohol, so the more sugar in the wine the more alcohol you'll get.... except for two little snags: First, yeast dies when the alcohol reaches ~22% (depending on the yeast) - I recall hearing that someone had developed a yeast that could tolerate nearly 30%, but who sells it? Second, too much concentration of sugar blocks the yeast from working.
Another little point of fact: the more sugar in the wine, the higher the gravity.... which means the higher any floating object will sit on the surface. Conversely: the more alcohol in the wine, the lower the gravity.
If you have a calibrated hydrometer and check starting gravity, then check again at intervals, you'll know roughly how much alcohol is being created. If your wine ends-up at '1' (Water, as reference, is '1'), then the alcohol will be exactly balancing the remaining sugar, so the wine will be slightly sweet (ie, 'medium'). For a dry wine you need a final gravity of ~0.99 or 0.98.
Most ingredients contain some sugar. Grapes have loads so needs no added sugar. Parsley has almost none, so all its sugar needs to be added. If the main ingredient is crushed (fruit) or boiled (vegetable) then the sugar should get released so that when you dissolve, say, 1Kg/gall(5-litres) of sugar into the 'must' (unfermented wine), the starting gravity reading should be accurate.
BUT intelligent guessing and tasting is a fine substitute if you don't have a hydrometer, so knowing what I've written above (and details like those in the chart below) is not essential. You can, if you like, skip all this sugar stuff and just get on with making the wine.
A 'Useful' Chart
The chart is copied from a book, and there's a formula I found in another book which goes:
Alcohol = (Start gravity - Finish gravity)/0.0736
That formula, disconcertingly (but not surprisingly), fails to tally with the chart. It's precisely this kind of typical inconsistency that led me many years ago to treat with a level of scepticism what I read in wine-making books - and most definitely where there's a recipe for sage wine! A quick surf of the web revealed a banana-wine recipe that to me is obvious tosh.
Hence, apart from the chart and formula, what you read on this site is from real experience... no make-believe, no conjecture, no blind copying. So you just have to strike lucky - or use common sense. I'd say, regard what you read as merely a guide, but above all you can't beat experience.