How to make concentrated juices
In the modern canning industry, fruit juices are concentrated mainly from apples, grapes, and citrus fruits (mandarins). Such juices contain from 50 to 70% of dry substances. Concentrated juices can reduce by 4-6 times the number of containers for packaging (compared with the original juice), the storage area for storing the finished product and vehicles for its transportation.
Three methods for producing juices have been developed: concentration by evaporation (thermal method), freezing and reverse osmosis.
The thermal method of concentrating the juice is carried out in high-performance vacuum evaporation plants, most often of film type, at a boiling point not higher than 50 ° C. The juice spreads in the apparatus with a thin film (about 1 mm thick) and decreases from 10 to 70% in just a few tens of seconds. This method gives good results for juices non-viscous, clarified, transparent.This method preserves the appearance, taste and color of the juice. To preserve the aroma of the product carry out the capture of aromatic substances, which are often easily volatile. When concentrating the juice, they evaporate and leave the apparatus along with the first portions of the juice vapor. These volatile aromatics trap and condense. Concentrated, cooled fragrances packaged in bottles. Before using concentrated juice, they can be returned to juice before diluting the concentrate with water.
Unclarified juices concentrate to 55% of dry matter, clarified — up to 70%, except for cranberry, which is concentrated to a dry matter content of 55%. Tangerine juice is concentrated to 45% solids.
Concentrated juice with a solids content of 70% immediately after boiling is packed into a prepared container (at a temperature of 40-50 ° C). When the content of 55% solids juice to prevent bacterial spoilage preserve sorbic acid or sterilized. When canning hot bottling concentrated juice after boiling quickly heated to 85-86 ° C and packaged in prepared hot jars.
Aromatic substances are stored separately from the juice concentrate added just before packing the concentrate into small containers for sale.
Concentration of reverse osmosis is intensively studied and attracted the attention of scientists in our country and abroad.
The separation of substances using a membrane under pressure is called ultrafiltration and reverse osmosis. Under the method of reverse osmosis understand the forced filtering of solutions through a semi-permeable membrane, permeable solvent molecules and trapping molecules or ions of dissolved substances. The phenomenon of osmosis is common in nature and is associated with the spontaneous transition of the solvent through a semipermeable wall.
If a pressure greater than osmotic is used, the solvent is transferred through the membrane in the opposite direction, which is the basis of the reverse osmosis method.
Ultrafiltration is the process of separating high-molecular and low-molecular compounds in the liquid phase on selective membranes that let in molecules of low-molecular compounds and retard high-molecular compounds.
Ultrafiltration is carried out at a relatively low pressure of 0.3 - 1.0 MPa and is used for clarification and stabilization of fruit juices.
Reverse osmosis processes are carried out at a pressure of 4.0-10.0 MPa. The devices of membrane separation for these processes are identical, only the pore sizes of the membranes are different. For reverse osmosis membranes have small pores (0.1-10 m) and high retention capacity.
Domestic industry mastered the production of cellulose-type membranes of the type “Vladipor”.
Research conducted by scientists on the use of reverse osmosis to concentrate fruit juices has shown that the use of this method is preferable to evaporation, because operating costs are reduced, thermal and oxidative degradation of the product is absent, and the preservation of aromatic substances is enhanced. The method is under development.
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