Had a look and those juices whilst out shopping today. 99p/litre was much cheaper than I expected (but the sign says "trial price"). The labelling of contents seemed rather defficient compared to the detailed info on virtually all products produced to be sold in the UK, so I checked the survey of preservatives in shop sold drinks on the FSA website, but it wasn't listed.
The strawberry juice interested me as itls very difficult to get hold of without additives/additional flavourings/etc., so I've bought one and added an activated yeast starter. I've not added/mixed it with anything else yet, because if it fails to start due to presence of preservatives I will only need to boil a litre of juice up to drive them off, rather than 4.5 litres.
It tasted really natural and quite sweet, but when I checked the sugar content and it contains 0.5Kg of sugar/gall (as expected from a juice drink).
As I intend mixing it (if it starts bubbling) with some blackcurrant and apple juice I am not worried about the acid content, but if it wasn't mentioned on the cherry (low acid fruit)juice label I might add a teaspoon of citric acid/juice of lemon per gall.
BUT IF it's OK, then 4 (would have suggested 5, but they + sugar wouldn't all fit in a demijohn) bottles of juice (don't rush out and buy them yet) with a total of 1.5lbs of sugar disolved in, keeping 0.5lbs of sugar and 1 bottle of juice back (in the fridge after opening) until any initial ferment dies down - keeping these back is important because of the amount of pulp in the juice that will rise to the top and spray out the airlock if the demijon is too full), then topping up to full gall with cooled, boiled water (probably about 225ml would be required). Or ferment it all in a covered bucket for 4 - 5 days, then strain into demikohn. I noticed it stated "pectin" amonst the ingredients on the strawberry juice - if it has that on the cherry juice label use double pectalase - 2 teaspons/gall.
So I will post again advising whether it's started fermenting, or if I had to boil it due to suspected undeclared preservative.
Edit - Looking good so far, tiny bubbles and the pulp is rsing to the top, but I've pitched in a yeast that was really going before, only to see it slow down due to presence of presrvative.