There are two important points to remember when making jams, jellies or marmalades:
1) There must be the correct proportions of juice, sugar, acid and pectin in order to form a
good gel. Checks that can be made to ensure that the proportions are correct are given in
Section 6.1. In general, slightly under-ripe fruits contain more acid and pectin than do overripe
fruits, but there are differences in the amounts of acid and pectin in different types of
fruit (Table 4.8).
2) Water must be boiled off quickly to concentrate the mixture before it darkens. If whole
fruit is used, there are two heating stages: at the start, the fruit is heated slowly to soften it
and to extract pectin; then the mixture is boiled rapidly until the sugar content reaches 68-
72%. This change in heat output requires a large and easily controllable burner. At a small
scale, a stainless steel pan and a gas burner can be used2
, but the mixture should be
constantly stirred to prevent it burning onto the base of the pan, particularly towards the
end of boiling when it thickens. At higher production rates, a double-jacketed pan is better
because it gives more even and faster heating and does not risk burning the product.
Methods to test for the correct point to stop boiling are described in Section 6.1and a
summary of common faults in jam making is shown in Table 4.10.