low pectin content fruit cannot be used for jam and jelly preparation
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Fruit Preserves, Jams, And Jellies
The making of jellies and other preserves is an old and popular process, providing a means of keeping fruits far beyond their normal storage life and sometimes making use of blemished or off-grade fruits that may not be ideal for fresh consumption. In jelly making, the goal is to produce a clear, brilliant gel from the juice of a chosen fruit. Jams are made from the entire fruit, including the pulp, while preserves are essentially jellies that contain whole or large pieces. Marmalade, usually made from citrus fruit, is a jellylike concentrate of prepared juice and sliced peel.
ingredients lower the pH of the preserve and bind may be done in a highly controlled vacuum kettle, in which flavour volatiles are captured and returned to
The exact amount of sugar needed depends on the acidity level, the natural sugar content, and the type of product desired. If sugar content is too low, the resulting jelly will be tough; excessive sugar, on the other hand, will create a “soft set” that can be broken easily. Appropriate amounts of acid and pectin are added during the cooking process. The pH must be adjusted to an acidic level of approximately 3.1. Increased acidity reduces the amount of sugar needed in the blend, although excessive acidity can cause syneresis, or a separation of liquid from the gel. If the pectin level is inadequate, then the preserve will not “set”; that is, not enough water will be bound to create a complete gel.
Dehydration
Dehydration is among the oldest and most common forms of fruit preservation. In dehydration, moisture in the fruit is driven off, leaving a stable food that has a moisture content below that at which microorganisms can grow. There are three basic systems for dehydration: sun drying, such as that used for raisins; hot-air dehydration; and freeze-drying.
Dehydration has a number of advantages. Dehydrated fruit has a virtually unlimited shelf life when held under proper storage conditions. Drying does not significantly reduce the calories or minerals, and vitamin losses are similar to other preservation methods. In addition, by reducing the weight and the need for refrigeration, handling and transportation costs can be reduced dramatically. Dehydrated fruits are typically reduced in weight by 75 to 90 percent.
Thermal processes
In thermal processing, heat is used to destroy spoilage organisms and to inactivate troublesome enzymes. Enzymes are typically responsible for browning, softening, and the development of off-flavours. For high-acid fruit products the most typical thermal process is canning, in which fruit or fruit products are hot-filled or heated in a hermetically sealed container. The process temperature is generally in the range of 88° C (190° F).
Chemical preservation
Chemicals also can be used as a preservative, either through artificial addition or through the action of microorganisms. An example of the latter method is yeast fermentation, which can cause an increase in ethyl alcohol sufficient to preserve the fruit product.
Although irradiation is an expensive method, it has been shown to be an effective means of extending the shelf life of fresh fruits. Irradiated fruit products have not been well received by the public, even in light of evidence supporting the texture upon thawing.
A prerequisite for effective freezing is inactivation of fruit enzymes. Traditionally, this is done through blanching or by the addition of a chemical. Blanching consists of heating the fruit for a short time in water or steam prior to cooling and subsequent freezing. The blanch step is intended to inactivate enzyme systems responsible for off-flavours, browning, and softening.