Ok, I'm patching this together from a bunch of different stuff I've read over the years. It's pretty skechty. Lemme know if I'm missing something.
1) Make a big supply concentrated sugar syrup. 24 Baume?
2) Prepare fruit base. Puree fruit, open bottle of juice, etc. Adjust flavors. Fiddle with stabilizers
3) 'Dilute' fruit base with sugar syrup until you get ~18 Baume
This is mostly for fresh fruit. I am a little worried that with low moisture fruit or a cooked fruit (say roasted/caramelized apple or pears) would have enough inherent water in them. So I'd have to add water. Don't have a general rule for that yet.
Also, not sure how I should address the issue of the invert sugars like HF and high DE corn syrup. I was thinking of including them in the main supply of sucrose syrup, but that would throw off the meaning of the Baume reading, because inverts lower the freezing point more then sucrose.
I suppose this could work with purees from manufactures. They seem to have their own ideas. I was looking at the fact sheet from Les Verges Boiron, they want atomized gloucoe, pfft
Or I suppose I should go rob a bank and buy a pacojet. Don't have to worry about the sciency stuff then.