Pectin test.

I thought I might add my two cents to conversations on the internet about pectin - particularly since the first one I found was atrocious:

Windygales, you obviously didn't know what you were talking about in your initial post, but thanks for the quick turnaround via BBC food. Her question actually wasn't 'what is pectin?' though, so your second answer is just as useless as your first.

The rest of the conversation has a similar confused, incorrect or speaking-just-for-the-sake-of-it tone.

Who doesn't have methylated spirits around their house? And why are they referred to as meths?

Pectin is a naturally occuring gelling agent in fruit. You can extract it by cooking beforehand. It is assisted by natural acids in the fruit, and you can increase the gelling process by adding lemon juice or tartaric acid. Over-ripe or stale fruit, as well as whole fruit cooked into a preserve, will have less pectin also. Do the pectin test before adding the sugar to determine how much you will need.

Fruits high in pectin and acid:

Currants (red, black and white)

Loganberries

Firm raspberries

Mulberries

Firm, ripe plums  (teehee)

Green apples

Quinces

Citrus

Fruits low in pectin or acid (little to none.)

Pears

Peaches

Sweet cherries

Very ripe grapes

Apricots

Strawberries

Melon

Overripe figs

How I pectin test (alcohol method):
Requires: methylated spirits, boiled fruit, a jar and a lid.

Cover fruit with water and cook between 15-45 minutes (depends on the type), and add 1 tablespoon of that liquid to a jar. Add 3 tablespoons of metho to the jar and shake thoroughly for a minute. Allow to stand for two minutes and pour from one container to another, or stir with a fork. If the mixture has clotted, there's plenty of pectin present and I will add 3/4 of a cup of sugar to one cup liquid, and about 50mLs of citrus juice per 2 cups of liquid.

If there is not, I will cook for another half hour, then re-test. If needed I will increase the sugar/liquid ratio to 1:1 and add an extra 25mls acid per cup, or purchase pectin from a store (absolutely last option, and I still haven't needed to buy any yet...)

For further reading, here's a page whose author knows how to make a jam or two. Maybe even jellies, curds and compotes. It's got good images of how to test for pectin, and gives you a few more choices than I have (jelmeter test, spoon sheet test, refractometer test).