It may be a little late for this now, but in retrospect it may not be and it can always be used for the forthcoming year.
If you have some apples starting to get a little bruised or have a load of crab apples left over from a foray into the countryside one way of using them up is to make your own pectin stock for use either later in the year or during the course of next.
Some fruit's don't have much pectin such as cherries figs grapes marrows pears pineapple rhubarb and strawberries which are classified as low pectin fruits; and occasionally possibly Apricots blackberries greengages loganberries and raspberries Medium pectin fruits will need a bit of a boost to help make any jams or jellies set properly.
High pectin fruits are citrus fruits (oranges lemons grapefruits etc) cooking apples, crab apples, cranberries, damsons, gooseberries plums and quinces.
Take your basic fruit, this may be Apple (any kind) redcurrant, gooseberry and damsons may all be used to produce pectin stock and be used to add to jams and jellies made from fruits low in pectin. It is quite easy to achieve this.
So prepare your fruits by putting in a pan with just enough water to cover and cook gently until fruit softens; strain through a jelly bag overnight and don't squeeze as this will produce a cloudy pectin stock which you don't want. Retain the syrup that has dripped through jelly bag and pop into a clean pan and bring to the boil. Then add to hot sterlised bottles/jars which are heatproof, seal and then immerse these in a deep pan of hot water where the bottles are covered topped to bottom in water (hot water bath processing) and boil for approximately 5 minutes (this removes any air which is chiefly responsible for causing foods to go off). Leave to cool. When coolness is achieved label. Put in your pantry until you need it.
To use: Any low pectin fruit should be well softened before adding the pectin stock. The amount of pectin varies as to what fruit is used but a general guide is 150 ml/ 5 fl oz pectin stock to 2kg(4lb) fruit.
If rather than make your own and a commercial variety of pectin is used 50-125 ml (2 to 4 fl oz).
If using dried pectin (these are occsionally available in little boxes containing sachets) 2 teaspoons of dried pectin to each 450g(1lb) of fruit.
If you make your own pectin stock this will save you having to purchase the commercial variety called Certo or the dried pectin powder from something that may be free from the countryside or just a little past its best. And it will be on the pantry shelf there ready to use when that batch of cherry jam just didn't set properly.