Preparation and extraction of juice
i. Selection of fruit:
Only fully ripe fruits are selected. Overripe and green fruits, if used, adversely affect the quality of the juice.
ii. Sorting and washing
Diseased, damaged (or) decayed fruits are rejected or trimmed. Dirt and spray residues of arsenic, lead, etc., are removed by washing with water or dilute hydrochloric acid (1 part acid 20 parts water).
iii. Juice extraction
Generally, the juice is extracted from fresh fruit by crushing and pressing them. Screw-type juice extractors, basket presses, or fruit pulpers are mostly used.
The method of extraction differs from fruit to fruit because of differences in their structure and composition. Before pressing, most fruits are crushed to facilitate the extraction. Some require heat processing for breaking up the juice–containing tissues. In the case of citrus fruits, the fruit is cut into halves, and the juice is extracted by light pressure in a juice extractor or by pressing the halves in small wooden juice extraction. Care should be taken to remove the rind of citrus fruits completely otherwise it makes the juice bitter. Finally, the juice is strained through a thick cloth or a sieve to remove the seeds. All equipments used in the preparation of fruit juices and squashes should be rust and acid-proof. Copper and iron vessels should be strictly avoided as these metals react with fruit acids and cause blackening of the product. Machines and equipment made of aluminum, stainless steel, etc. can be used. Extracted juices should not be unnecessarily exposed to air as it will spoil the colour, taste, and aroma and also reduce the vitamin content.
Fruit juices contain some air, most of which is present on the surface of the juice and some is dissolved in it. Most of the air as well as other gases are removed by subjecting the fresh juice to a high vacuum. This process is called deaeration and the equipment used for the purpose is called a deaerator. Being a very expensive method, it is not used in India at present.
v. Straining (or) Filtration
Fruit juices always contain varying amounts of suspended matter consisting of broken fruit tissue, seed, skin, gums, pectic substances, and protein in colloidal suspension. Seeds and pieces of pulp and skin which adversely affect the quality of juice, are removed by straining through a thick cloth or sieve. Removal of all suspended matter improves the appearance but often results in the disappearance of fruity character and flavour. The present practice is to let fruit juices and beverages retain a cloudy or pulpy appearance to some extent. In the case of grape juice, apple juice and lime juice cordial, however, a brilliantly clear appearance is preferred.
Complete removal of all suspended material from juice, as in lime juice cordial, is known as clarification which is closely related to the quality, appearance, and flavour of the juice. The following methods of clarification are used (a) Settling (b) filtration (c) freezing (D) cold storage (e) high temperatures (f) chemicals such as gelatin, albumen, casein, the mixture of tannin and gelatin (g) enzymes such as pectinol and filtragol.
vii. Addition of sugar
All juices are sweetened by adding sugar, except those of grape and apple. Sugar also acts as a preservative for the flavour and colour and prolongs the keeping quality. Sugar-based products can be divided into 3 groups on the basis of sugar content.
- Low sugar – 30 per cent sugar or below
- Medium sugar – sugar above 30 and below 50%
- High sugar – 50% sugar and above
Sugar can be added directly to the juice or as a syrup made by dissolving it in hot water, clarifying by the addition of a small quantity of citric acid or a few drops of lime juice and filtering.
Juices, squashes, syrups, etc. are sometimes fortified with vitamins to enhance their nutritive value, to improve taste, texture, or colour, and to replace nutrients lost in processing.
Usually, ascorbic acid and Beta-carotene (water-soluble form) are added at the rate of 250-500 mg and 7-10 mg per litre, respectively. Ascorbic acid acts as an antioxidant and beta-carotene imparts an attractive orange colour. For a balanced taste some acids are added. Citric acid is often used for all types of beverages and phosphoric acid for cola-type of drinks.
Fruit juices, RTS, and nectars are preserved by pasteurization but sometimes chemical preservatives are used. Squashes, crushes and cordials are preserved only by adding chemicals. In the case of syrup, the sugar concentration is sufficient to prevent spoilage. Fruit juice concentrates are preserved by heating, freezing, or adding chemicals.
x. Preservation by Bottling
Bottles are thoroughly washed with hot water and filled leaving 1.5-2.5 cm headspace. They are then sealed either with crown corks (by crown corking machine) or with caps (by capping machine).
Juices are of two types
- Natural juice (pure juice): It is the juice, extracted from ripe fruits, and contains only natural sugars.
- Sweetened juice: It is a liquid product which contains at least 85% juice and 10% TSS.
Pure fruit juices such as apple juice and orange juice are commercially manufactured. Apple juice is generally bottled while other juices are canned.
A. Apple juice
Apples → Washing with 1.5% Hcl – Grating (apple grater)→ Crushing for juice extraction → Straining → Clarification (By enzyme (or) gelatin) → Filtration→ Heating at 82-85oC → Filling hot into cans →Sealing → Processing at 100oC for 15 min. → Cooling → Storage.
B. Citrus juice
Mandarin and sweet oranges → Washing → Peeling (By hand) → Separation and cleaning of segments → Juice extraction (Screw type extractor) → Straining → Heating at 80oC – Bottling (or) canning (Baby food cans) → Crown corking (or) can sealing →Pasteurization → Cooling → Storage.