Making jam at home is an ideal way of preserving fruit in season for use throughout the year. Good home-made jam has a very good, fruity flavour, a clear bright colour, a firm set, and will keep well.
Jam is made from two main ingredients, fruit and sugar. The fruit has to contain plenty of pectin and acid if it is to set properly. Some fruits contain plenty of pectin and acid and so will set easily. These are often the hard sour fruits such as plums or damsons. Other fruits contain less pectin and acid, so to make sure that the jam sets well you have to add pectin or acid in some form.
Fruits which contain plenty of pectin and acid and so set easily
Fruits with a moderate amount of pectin and acid
Fruits with low pectin and acid content which do not set well
Pectin is a gum-like substance found in the cell walls of ripe fruit in varying amounts. In under-ripe fruit it is in the form of pectose which can be turned to pectin when the fruit is stewed with an acid. In over-ripe fruit the pectin has turned to pectic acid and has lost its setting properties.
This means that you should choose fruit which is either ripe or under-ripe for making jam. Avoid fruits which are over-ripe as results are likely to be poor.
If the fruit you are using is low in pectin you can add to it either:
1 Some fruit of a kind with plenty of pectin, e.g. apples to blackberries, gooseberries or blackcurrants to strawberries.
2 Pectin in powder or liquid form, e.g. Certo'. Buy this from a chemist or grocer.
Acid is needed in jam
1 To convert any pectose to pectin and thus help it to set.
2 To improve the flavour and colour of the jam.
3 To prevent hard crystals of sugar forming in the jam when you store it.
If you are using fruits which are low in acid you can add it in the form of one of the following, before you start to cook the fruit:
4 Lemon juice (about 2 tablespoons to each 1 kg/2Ib of fruit).
5 Citric or tartaric acid, or cream of tartar ( ½-1 level teaspoon for each 1 kg/2lbs fruit). You can buy this at a chemist's or grocer's.
Use granulated sugar as it is cheapest and gives good results. You can buy special preserving sugar. This is meant to dissolve more easily and to produce a little less scum, but it is more expensive and not really necessary.
General method for making Jam
1 Prepare the jam jars.
2 Prepare the fruit according to what kind it is and cook gently until completely soft
3 Add the sugar and dissolve thoroughly.
4 Boil vigorously until setting point is reached.
5 Pour into the jars, cover, and label.
To prepare the jam jars
It is essential that these are clean, dry, and warm. Wash them thoroughly in warm, soapy water, rinse, and drain. Dry the outsides with a clean tea-towel.
Warm the jars by standing them on a wooden board on the floor of a your low oven or by placing them above a warm cooker.
To test for setting point
Once the sugar has been dissolved in the cooked fruit, the jam is vigorously boiled until setting point is reached, usually in about 15-20 minutes.
You have to test the jam to see if it has reached this point. There are several tests:
The wrinkle test
This is the simplest method.Place a small saucer in the fridge.
When you think that the jam may have reached setting point, remove it from the heat. Put a small teaspoon of jam on to the cold plate and let it cool a little.
Push the jam with your fingertips over the plate. If it wrinkles on the surface the jam should set. If not, boil for a little longer and test again.
The flake test
Use a clean, dry, wooden spoon to remove a little jam from the pan. Allow it to cool slightly. Gently pour the jam over the side of the spoon.
If it comes off in wide flakes it is ready. If it pours off the spoon in a thin trickle it is not.
The thermometer test
The jam should reach a temperature of 104'C or 1 05'C before it has the sugar concentration of 65% which is necessary for it to set.
Keep the thermometer in a pan of boiling water beside the jam pan. It enables you to check it for accuracy (the water boils at 100'C) and makes the thermometer easier to clean.
Scum is just made up of small bubbles of air which have been caught up in the sticky, boiling jam. It is harmless, but spoils the appearance of the jam. Once the jam has reached setting point, remove it from the heat. Stir in a small piece of butter or margarine. This will disperse most of the scum from the jam. If any remains, remove it with a metal spoon.Filling the jars
This should be done while the jam is very hot, unless you are making strawberry jam or marmalade.
With these, you allow the jam to cool for 15 minutes in the pan, so that all the fruit does not rise to the top of the jar.
Fill the jars very carefully as the hot jam can scald your hands badly. Use a jug to scoop the jam out of the pan. Scrape the bottom of the jug on the edge of the pan, then pour the jam into the jars. Fill them right to the top as jam shrinks when it cools.
Stand the jars on a board or baking tray and position each one right at the edge of the pan before you fill it. This keeps the outside of the jars clean and avoids splashes. Never hold a jar in your hands while pouring hot jam into it.
To cover the jars
As soon as you have filled them, place a waxed disc over the jam, wax side down. Damp the cellophane covers in a saucer of water, on one side only.
Place the dry side down, and secure with an elastic band. You can use jars with screw-top lids instead of cellophane tops.
Remove any splashes from the outside of the jars with a damp cloth. Place a label on the jar with the name of the jam and date.
If you want to decorate the jars with small circles or squares of cotton tabric, place these over the cellophane cover or screw-top jar and secure with an elastic band. Store the jam in a cool, dry, dark place.
Common faults in making jam
Jam will not set.
The jam has not been boiled for long enough and so has not reached setting point.
The fruit is over-ripe.
Fruit is of a kind low in pectin or acid and you
have not added anything to counteract this, e.g. lemon juice, cream of tartar.
Jam goes mouldy or ferments.
Not enough sugar.
Storing in a damp, warm place.
Crystals in the jam.
Jam has been boiled too long.
Too little acid.
Jam which is thick and stiff.
Boiled for too long past setting point.
Fruit which is tough and hard.
Fruit not properly cooked before sugar is added.