Fruit and Vegetable Processing
* 1 Kg Pectin extract
* 1 Kg Sugar
* 10 gms ready made fruit pectin
* 7 gms citric acid.
Ripe but not over ripe fruits are selected slightly unripe yields more pectin than over ripe fruits, because as the fruit ripens the pectin presents in it, decomposes into peptic acid which does not form into jelly with acid and sugar, under ripe fruits for their Pectin content and ripe ones for their flavour. Generally, fruits like guava, apples are not required to peel, they are only washed and cut into thin slices of not less than ½" thickness.
Extraction of Pectin or Fruit Extract
Fruit slices are boiled with equal volume of water (i.e,. 2 Kg water to 1 Kg fruit in case of guava and oranges) without stirring. In case of highly juicy fruits (i.e, berries like grapes etc.) the fruits are merely crushed and boiled without addition of water.
Time required for boiling (optimum)
* Apple - 20-25 minutes
* Guava - 30-35 minutes
* Orange - 45-60 minutes
Pectin Content Test
Pectin content of fruit extract may be determined by taking 1 ml of boiled fruit extract in a test tube and add 3 ml alcohol (90%) in the test tube and leave for few minutes till clotting is formed. If a single clot is formed, it indicates that the fruit extract contains rich pectin, where as if small unstable clot is formed it indicates poor pectin.
The pectin extract or fruit extract may be pass through bags of linen, flannel or through felt or cheese cloth folded several times to obtain a clear extract. The bags or cloth should be first scalded in boiling water, squeeze and use while still hot and wet (Bags containing fruit extract should be squeeze otherwise the extract will not be due to fruit particles passing through the pores in the bag).
Adding of Sugar and Cooking
Generally equal quantity of sugar (i.e., 1 Kg sugar, 1Kg pectin extract) is sprinkled over the pectin while it is boiling with continuous stirring to ensure complete dissolution of sugar. The mixture is then filtered through a muslin cloth to remove impurities and boil all over again in a brisk fire till it starts boiling, sprinkle 10 gms ready made fruit pectin mixed with small quantity of sugar (10 gms) over the mixture and add citric acid just before the end point, i.e,. when temperature reaches 221°F or total soluble solids reached 65°Brix as measured with a Brix metre.
Determination of End Point
If refractometer and thermometer are not available the following simple test may be adopted to ensure whether the jelly is set or not.
* Cold plate test : A drop of the boiling liquid from the pan is taken and placed on a plate and allowed to cool quickly. If the jelly is about to set, the mixture on the plate will crinkle when pushed with the finger. The main drawback of this method is that while the drop on the plate is cooling, the jelly mixture continued to boil in the pan with the result that there is risk of over-cooking the product or of missing the correct setting point.
* Sheet or Flake test : In this case a small portion of the jelly is taken with a large spoon or wooden ladle and allowed to cool for a few seconds and let it drop. If the jelly drops like syrup, it requires further concentration but if it falls in the form of flakes or sheet the end point has reached.