Fruits vary a great deal in how much pectin or pectin precursors are present. Raspberries and strawberries, for instance, are low in pectin, while apples, citrus fruits, gooseberries and currants are high.
Pectin can be extracted from high-pectin fruits and added to low-pectin ones to make better jams with less cooking.
Commercial pectin today is usually extracted from the white inner part of citrus skins or apples.
Pectin produces structure and a kind of stiffness in jams by forming a water-holding network within the juice or crushed fruit. Before jelling starts, individual molecules of pectin are surrounded and isolated from each other by water molecules. If the surrounding solution is acid enough, the pectin loses some of its attraction for these isolating water molecules. Sour fruit will normally provide enough acid to take care of this step. If the acid content of the fruit is low, lemon juice can be added to make the fruit mixture more acid.
Once the pectin has loosened its hold on the water molecules, something more attractive must pull the water away from the pectin. This is the role of sugar. Artificial sweeteners may affect taste, but they do not attract water as sugar does. This is why ordinary pectin cannot be used to make jellies without sugar.
With its water stripped away, pectin opens out into a structure which links readily with other pectin molecules to form a three dimensional network. This network is what gives the stiffness to the finished product.
Underripe fruit has more pectin than fully ripe. Jams made without added pectin should use 25% under ripe fruit.
Pectin is concentrated in the skins and cores of fruit, that is why recipes call for these to be included. They are best tied up in a square of muslin and placed in with the main ingredients.
Some recipes call for a second cooking, this extracts more pectin as in the marmalade recipe.
Commercial pectin's may be used with any fruit. These are sold as 'Jam sugar' (sugar with added pectin) or as liquid, usually extracted from apples or citrus fruit.
Jams made with added pectin require less cooking times and generally give larger yields.
Adding a small nugget of butter will reduce foaming, with jams made with extra pectin.
Another way is to add a cooking apple, chopped and tied up in a muslin square. Cook at the same time as the main ingredients. Any lemons left after the juice has been extracted, can also be added to the muslin bag.
Combining poor pectin fruit with high pectin fruit is another way to ensure that a good set is obtained. Combinations are blackcurrant and rhubarb, gooseberry and strawberry or loganberry and raspberry.
Home-made pectin
Pectin is most effective when extracted from high content fruits cooking apples, gooseberries and redcurrant.
The complete fruit is used as the skin or cores contain the highest content.
Wash 1kg / 2 lb of fruit. If apples, chop coarsely. Place in saucepan with 750ml / 1¼ pints of water
bring to the boil, turn down heat, simmer for 40 minutes until pulped. Strain through a jelly bag, test pectin strength by mixing a teaspoon of liquid
in a cup and with three teaspoons of methylated spirits. Swill contents together allow to cool and pour away methylated spirits. If liquid has formed a clot
then the pectin of liquid is high, if liquid has formed separated clots then cook for a further 10-15 minutes.
Only use if pectin content is high.
Use 150-300ml / ¼-½ pint of pectin extract, with 2kg / 4 lb of low pectin fruit.
Acid in jams
Acid is needed in jam making for flavour and gel formation. The acid content varies in different fruits and is higher in underripe fruits. Most fruits supply enough acid for gel formation. If additional acid is needed, the recipe will call for lemon juice. Commercial pectin products contain acids which help to ensure gelling.
