Want to know what to look out for when picking or buying fruit for jam? Or what proportion of fruit to sugar is best? Delia has all the answers...
Home-made jams are made from just two ingredients, fruit and sugar, unlike some of their cousins on the supermarket shelves. In fact, I am a passionate studier of labels and have rarely come across any commercially made jam or marmalade that contains only fruit and sugar. So, both in terms of quality and economy, it makes sense to make them at home and add that touch of luxury to everyday eating.
Jam is essentially preserved fruit. The fruit, if it’s in good condition (and slightly under-ripe) contains in its cell walls a natural setting agent called pectin. This, together with the natural acid from the fruit, is released when the fruit is boiled with sugar. As it boils, the sugar concentrates and all three – sugar, acid and pectin – combine to form a mass that eventually reaches ‘setting point’.
The vital point to remember is that all ingredients like fruit and vegetables for preserving must be sound. Anything that looks damaged or decayed in the slightest way should not be used. The fruit should also be dry, since the water content of damp fruit will dilute the pectin and the acid and render them less active. Any dusty fruit should only be wiped with damp kitchen paper, and anyway, the boiling will effectively purify the fruit. Slightly under-ripe fruit actually contains more pectin and fruit acid than over-ripe fruit (which should therefore be avoided). With those fruits that contain less acid than others, this deficiency is made up by adding lemon juice.
The proportion of sugar to fruit varies according to the type of fruit used. I believe really sharp fruits, such as damsons or loganberries, make the best jams because they are not overpowered by the sweetness of the sugar, and the fruit flavour is predominant. This is also why I think Seville oranges make the best marmalade, tasting of oranges rather than sugar. Of course, other fruits also make good jams – providing the fruit content is high and there’s not too much sugar.