From The Preservatorium preserving book. This will help set preserves made with low-pectin fruit. I prefer it to using commercial pectin which usually calls for huge amounts of sugar. Sure, the set will not be as "stiff" but I prefer the taste and texture.
Lee Murphy, the author, recommends using green, unripe apples, but if you can't find them, use tart Granny Smith apples.
This is super easy to make!
This recipe makes about 5 1/2 litres.
7 lbs green apples (stems removed and quartered)
12 cups water
In a large stockpot, bring the apples and the water to a boil over high heat. Cook the apples until they are falling apart, about 20 - 30 minutes.
In a food processor or food mill, pulse in small batches to create a mash, strain through a sieve or chinois. For a clearer juice, line the sieve with cheesecloth.
Freeze in smaller containers for use in preserving recipes. Keeps for six to nine months.