Apple pectin

To prepare liquid apple pectin, it is best to use under-ripe apples that are still a bit green, hard, and sour. Ripe apples contain less pectin, but the level varies greatly from one tree to the next; some varieties are suitable when ripe, while some have virtually no pectin by that time. Over-ripe apples are the worst. You can use your damaged or misshapen apples for making pectin. Chop them in halves or quarters, fill a large pot, and then add just enough water to almost cover the apple chunks. Cover the pot and place it on low heat for a long time, until the apples are fully cooked and you have something that looks like runny applesauce with skins and seeds in it. Stir the apples every twenty minutes or so while they are cooking.

Arrange a strainer for this "sauce" by placing a cheese cloth (actually a white T-shirt) over the top of a five-gallon pail, secured by a cord tied around the rim. (A piece of cheese cloth in a colander works fine for smaller amounts.) The hot applesauce is then poured into the strainer; what drips out the bottom should be a clear, thick liquid that's a little bit slimy to the touch. That's your liquid apple pectin. I usually let mine strain overnight, because it drips slowly. You can get more pectin by pressing it, but then it comes out a little cloudy and carries more of the under-ripe apple flavor. I like to make a few gallons of this pectin at a time and then save it by canning or freezing - it's not hard to get a year's supply with one batch.

To test the strength of the pectin, pour a little bit of rubbing alcohol into a glass and then drop in a spoonful of pectin. The pectin will coagulate into a jelly-like mass. If this mass can be pulled out with a fork and it forms a heaping gob on the tines, it is concentrated enough to jell perfectly. If it can be picked up by the fork, but mostly hangs from it, then it will jell loosely. If it cannot be picked up by the fork in mostly one mass, then the concentration is too weak for it to jell. In this latter case, you just have to boil it down to increase the concentration of the pectin. (Note: the alcohol test doesn't work right if the pectin is hot.)
You mix this green apple juice with the blackberries and sugar and boil until it coats a spoon. Bingo jelly!