Aww, poor little blackcurrant, not even able to unite with its brethren by being eaten.
By the way, I previously missed Jude's question about crabapple jelly. I have an apple jelly recipe that should work just the same for crabapples (although test the sweetness of the result, as crabapples are often less sweet than other apples). I'll copy it here for you:
Ingredients:
2kg apples
juice of 1 lemon
water to cover
1 cup of sugar for each cup of juice
Method:
Leaving apples unpeeled and uncored, cut into pieces and place in saucepan with water to cover (and presumably the lemon juice, although the book doesn't say). Simmer for 45 minutes to an hour or until fruit is quite tender.
Strain fruit through a sterilised cheesecloth and leave to drip overnight. Do not squeeze the cheesecloth, as this can make your jelly cloudy.
Measure liquid (tip: use digital scales to weigh it as it goes into the pot), and add an equal volume of warmed sugar. Heat juice and sugar, stirring until sugar dissolves, then cease stirring.
Boil rapidly until jelly sets when tested. Start testing after jelly has been boiling for ten minutes.
When setting point is reached, remove scum before filling sterilised jars.
I like to test the jelly with a cold plate/saucer. I keep the plate in the freezer until the test, then drop a teaspoon of jelly onto it. If after one minute, the jelly stays put when the plate is tilted, it's ready. I think there's a method involving dropping a teaspoon of jelly into cold water, but I haven't used it.
Jars can be sterilised in various methods. If you use a water bath, be sure the jars are completely dry before putting the jelly in, or they can crack. I prefer to sterilise my jars in the oven (set it to about 120 C to allow for any variation from thermostat temperature, and leave in for ten minutes or until you need them). Be sure to only put hot liquid into hot jars.
The tips are advice based on me not knowing what you already know. If you have your own way of doing those things, feel free to ignore mine.