Is there any way of reducing the acidity of fruit other than by
smothering it with pounds of sugar? I'm wondering if there's any cooking
method or other treatment available to the ordinary person. I like the
very tart fruits like gooseberries, blackcurrant and rhubarb (nominal
fruit) for desserts and jams but worry about the amounts of sugar I take
in.

Secondary question: I notice most of the low- or no-sugar jam recipes
emanate from the US and call for frozen apple juice concentrate. I know
this is widely available over there but I've never seen it in this
country, does anyone know if it's available here?

TIA

Brian Mitchell