Making Fruit Juice

[Alaric]

I've been using an excess of summer fruit to make ny own juice. It's quite simple. Put fruit, water and sweetener in a jug and mash it with an electric mixer. Then strain to get clear juice. What I have found is that lemon juice is essential, not necessarily for flavour, but to stop the juice fermenting. I don't keep it for very long, not more than a week, but even then it would go effervescent almost immediately.

[Urbandreamer]

I've been using an excess of summer fruit to make ny own juice. It's quite simple. Put fruit, water and sweetener in a jug and mash it with an electric mixer. Then strain to get clear juice. What I have found is that lemon juice is essential, not necessarily for flavour, but to stop the juice fermenting. I don't keep it for very long, not more than a week, but even then it would go effervescent almost immediately.

Personally I have no problem with the idea of alcoholic drinks and might be tempted to add yeast.
However have you considered using wine or cider vinegar?
Shrub
https://www.youtube.com/watch?v=3AWqxSnArKk
https://www.youtube.com/watch?v=hH-XAm8ucWk

[UncleEbenezer]

I have a juicer that creates delicious drinks from a range of fruit and veg - and even spices. Akin to the "smoothie"s served in cafes. You can buy them from Usual Suspect retailers of kitchen appliances if you like your juices. Downside is that it's a bugger to wash up: several big parts take up a lot of dishwasher space, and pulp has to be scraped from the thin mesh first!

Fruits (and many veg) are our greatest source of good, natural sugars. Not to mention what some in the medical media describe as excess sugar! Why on Earth would you add sweeteners to something that is already the sweetest thing in an adult diet?

I wouldn't normally want to water it down either, beyond the effect of ice cubes. Just as I wouldn't water down most wines. But that's probably a matter of custom: living in Italy taught me that watering down the local wine - as the locals do - can work very well!

As for lemon? Works well with some fruits, but I would rarely combine it with non-citrus. Indeed, it can be quite unpleasant in combination with some otherwise-delicious juice. But then I drink a lot of it, so it has never had to last a week!