Manufacturing of fruit jam

Jam is made from crushed or ground fruit. The end product is less firm than jelly, but still holds its shape. The fruit content must be at least 40%. In mixed fruit jams the first-named fruit must be at least 50% of the total fruit. The total sugar content must be no less than 68%. In tropical climates, 70% sugar is preferable.

Fruit furnishes the flavor and part of the needed pectin and acid. Some irregular and imperfect fruit can be used.

In the manufacture of jam, the deforested fruit is passed through a pulper that allows essentially all the berries with the seeds to pass through the strainer.

Sugar and water are then added the amount of sugar depending on whether the frozen product was packed with or without sugar. About 0.1 – 0.15% dispersed pectin is then added and the product is heated in open kettles to concentrate it to soluble solids content about 68%.

When a commercial pectin is added, fully ripe fruit can be used. The use of this added pectin also increases the yield from a recipe.

Citric acid solution is then added to adjust the pH to 3.3 and the fruit is packed in glass jars and vacuum capped. The jars should be clean and sterilised. The ideal temperature for pouring is 82-85°C. Hotter than this and condensation will form under the lid. This will drop down and dilute the jam, allowing mould to grow. Colder than this and the jam will be difficult to pour.
Manufacturing of fruit jam

Processing of blackberries

More than 80% of the US production of blackberries in recent years has come from the Pacific Coast. The major blackberry-producing areas are Washington and Oregon. Blackberries grow on 2-yr old brambles or canes. Blackberries are very suitable for jam, marmalade and jelly as well as compote, sorbet, ice cream and parfait.

At the processing plant, the fruit is washed, inspected – to remove leaves, twigs, etc., and cooled to 32F. The fruit is held at this temperature until sold as fresh in retail sized baskets overwrapped with clear plastic or until it is processed.

Blackberries are harvested after ripening but before they have become soft and mushy. It is very unwise to allow the berries to become overripe, because they are then very susceptible to mold.

Blackberries should be thoroughly ripe when picked for freezing: otherwise they may turn red on freezing. The fruit is individually frozen in a cold air tunnel and packed in large metal cans with cap-type covers and held frozen. When the berries are to be used for producing jam and jelly, sugar is added to the cans so that the ratio of fruit to sugar is 5:1.

For producing jam, frozen fruit from cans is defrosted. The amount of sugar added results in a fruit to sugar ratio of 1:1. The pectin must be dispersed in the water before added to the mix. Water evaporated during the heating results in soluble solids content of 68%.

Blackberry jelly is produced by a similar process except that only clear juice is used, the amount of pectin is doubled, the soluble solids contents 65%, and the PH is adjusted to 2.9 – 3.2. Some blackberries are canned and heat-processed in water or light syrup for use as pie filling or in syrup for use in other desserts.
Processing of blackberries