Ive kinda made similar stuff (Im living in the uk) there isn't much available in the way of grape juice locally by me although I kinda prefer white I can get the ingredients for a red far more easily, although I cant get much in the way of white grape their is 2 veg shops close by, so ive kinda experimented with a mixture of real fruit and grape concentrate.
locally I cannot get white grape juice and there is only 2 red grape juices I can find locally one is welches red but low sugar the other is a Spanish red grape, I tend to mix one litre of each per gallon, with a combination of raspberry from cartons and black currant (reconstituted Ribena, watered down 4 to 1 and used the same as the carton juice then) recently ive tried red plums at a rate of one container ie 6 plums per gallon, de piped and sliced leaving the skins on.
taste wise, raspberry tends to give a slightly dryish flavour which is quite pronounced, the Ribena gives a bit of a more mellow raspberry hit, the plums tend to give a very mellow kinda taste, think merlot type flavour from plums.
If u use real fruit I tend to remove the fruit after about 7 days using a sieve, this is quite important as it prevents off flavours from rotting fruit, in my experience, by that time most of the sugar is alcohol and the fruit is beginning to look a bit sad any way.
as a rough guide ive found 2 litres of grape, plus, up to 1/3 rd of other juice combinations work well per gallon I also add between 1/2 to 1 kg per gallon of sugar, which usually ends up around the 13.5 to 14 % abv region.
hint if you read tasting notes for a particular red grape wine eg merlot cabernet etc you can add small amounts of fruit mentioned in the tasting notes to arrive at a desired flavour, also don't forget to use a source of oak, which makes a red nicer usually.
its my experience that carton juice on their own are quite bland unless u add extra fruit to tweak them.
If u get stuff floating on top use a syphon to get rid of it, fruit sediment which sinks is fine provided it passes through a sieve, in my experience and likely adds to the flavour once its matured, if your after a burgundy kinda taste, leave the wine siting on the sediment which has sunk, while it matures, anything which floats can add off flavours.
thinking strawberry and other fruits with tiny seed pips, these need filtering with a fine cloth filter, the tiny pips if left in the sediment produce an excess of tannin from the pips and a decidedly bitter taste, I expect most other pips to have the same effect, so best to remove pips after around 7 days or so, by whatever means u need ie big pips pick them out eg plum stones if u use them for finer pips filtering may be required.
welches on its own ive found to finish slightly sweet and slightly bland with little character, to speak of, hence the tweaks, although its a perfectly fine base grape juice.
Hope it turns out ok.
Arne.
