Based on the form in which the fruit is used, preserved products may be classified as:
- Jams, jellies, marmalade, cheese, toffee made from fruit in small pieces/ pulp/ juice
- Preserves, crystallized, glazed, candied fruits made from whole fruit/ big pieces
Jams are usually made from the pulp of the whole fruit . Three constituents namely pectin, sugar and acid are important in the preparation of jam. It can be made from one kind of fruit or from two or more kinds. Jam should have fruit content of at least 40 per cent and a total sugar content of not less than 68 per cent to prevent mould growth after opening the jar. Jams contain 0.5-0.6 per cent acid and invert sugar should not be more than 40 per cent. In India, fruits good for making jams are pineapples, mango (both ripe as well as raw), peach, pear, karonda, papaya, carrot, plum, apricot, apple, strawberry and gooseberry (rasbhari).
The whole fruit (strawberry, gooseberry) or the chopped pulp (mangoes, peaches, apples) of the fruit is cooked with a certain quantity of sugar (0.75 to 1.0 kg sugar for 1.0 kg fruit pulp) to a setting consistency, thick enough to hold the fruit tissues in position. If the fruit is not acidic enough, citric acid or lime juice is added to improve the flavour and the setting property.
Jelly is a crystal-clear jam but made only from the juice of the fruit. A clear juice extract, containing enough amount of pectin and acid, is boiled with certain proportion of sugar (0.75 to 1.0 kg sugar for 1.0 kg extract) to a consistency at which it will set on cooling. A perfect jelly should have a beautiful colour, should be transparent and firm, and on touching should quiver; it should not be syrupy like honey, sticky or have crystallized sugar; one should be able to cut it with a spoon and the spoon should come out clean.
Fruits like guava, apple, plum, karonda and papaya are generally used for jelly making. Some fruits which do not contain enough pectin like apricot, pineapple, strawberry, raspberry etc. can be used for jelly preparation only after addition of pectin powder.
Marmalade is made with the juice extract of citrus fruits like oranges and lemons with thin slices of the skin or the fruit suspended in the clear jelly-like mixture. Pectin and acid are both essential for the jelly-like consistency of marmalades. The proportion of sugar to juice is the same in a jelly.
Fruit bar or leather
In this, the fruit pulp is taken and its total soluble solids (TSS) content is raised to 30°Brix by adding sugar. This pulp is then spread on stainless steel trays smeared with fat which are dried in a mechanical dehydrator at 60±5°C for 2 hours. Potassium metabisulphite is added at the rate 0.2 per cent in the fruit pulp. Thin layer of pulp is dried on a pre-greased stainless steel or aluminum tray followed by second layer. Usually five layers are dried one above the other and the final product is packed in polythene bags. Fruit leather can be prepared from different fruit pulps like mango, peach, plum, apricot, papaya, etc.
Fruit toffees are made by mixing fruit pulp with other ingredients like glucose, milk powder and edible fat . The fruit pulp is first concentrated to half its volume in a steam jacketed kettle or pan over steam bath. Generally, for one kilo gram of concentrated pulp, 160 g of glucose, 320 g of milk powder and 200 g of edible fat is added. This mixture is further heated to a thick consistency (75- 80°Brix) followed by spreading it as a sheet of one cm thickness on a fat smeared flat tray and allowed to cool. Then these are cut into pieces (called as toffees) of desired size, wrapped and stored it in cool dry place.
Preserves or murabbas
A preserve is a product in which a mature fruit/ vegetable or its pieces are saturated with heavy sugar syrup. Shape of the fruit or the pieces is carefully preserved. Fruit pieces should remain tender, plump, glistening, firm and transparent. Care should be taken so that the flavour of the fruit is not masked by an excess of sugar. Fruits like Indian gooseberry (aonla), wood apple (bael), apple, pear, mango, cherry, karonda, papaya, pineapple and strawberry can be used for making preserves. These are made either with the whole fruit; particularly if the fruit is small in size or with uniformly cut pieces of the fruit like in the case of apples.
Candied fruits are first impregnated with cane sugar or glucose syrup and subsequently drained free of syrup and dried. These must be plump, tender and have highly flavoured sweet taste without any stickiness. The most suitable fruits for candying are aonla, karonda, pineapple, cherry, papaya, apple, peach and peels of orange, lemon, grapefruit, ginger etc.
Candied fruits covered with a thin transparent coating of sugar, which imparts them a glossy appearance, are known as glazed fruits .
Candied fruits when covered or coated with crystals of sugar, either by rolling in finely powdered sugar or by allowing sugar crystals to deposit on them from dense syrup are called crystallized fruits.