Fruit processing, evaporation

It is also worth noting that Alfa Laval has developed a process evaporator for fruit juice and milk concentration using a nested stack of cones. Figure 16... 

A typical fruit juice evaporation system using the heat pump cycle is shown (PI, Cl), which uses low-temperature ammonia as the heating fluid. A frozen concentrated citrus juice process is described by Charm (Cl). The process uses a multistage falling-film evaporator. A major fault of concentrated orange juice is a flat flavor due to the loss of volatile constituents during evaporation. To overcome this, a portion of the fresh pulpy juice bypasses the evaporation cycle and is blended with the evaporated concentrate. 

Developments continue on citrus fruit processing. The membrane configurations most often used in juice clarification are tubular membranes or hollow fibre modules, as well as plate and frame systems using flat sheet membranes. The traditional method of concentrating juices and purees has been evaporation, but nowadays reverse osmosis is proving successful. Reverse osmosis plant performance depends on juice viscosity, the osmotic pressure of the solution, and the constraints imposed by the need for a particular product quality. 

Freeze Crystallization. Freezing may be used to form pure ice crystals, which are then removed from the slurry by screens sized to pass the fine sohds but to catch the crystals and leave behind a more concentrated slurry. The process has been considered mostly for solutions, not suspensions. However, freeze crystallization has been tested for concentrating orange juice where sohds are present (see Fruit juices). Commercial apphcations include fmit juices, coffee, beer, wine (qv), and vinegar (qv). A test on milk was begun in 1989 (123). Freeze crystallization has concentrated pulp and paper black hquor from 6% to 30% dissolved sohds and showed energy savings of over 75% compared with multiple-effect evaporation. Only 35—46 kJ/kg (15—20 Btu/lb) of water removed was consumed in the process (124). 

These evaporators operated somewhere between 48.9° and 82.2°C (120°-180°F). Fruit solids remained in these evaporators for a minimum of 30 minutes hence, the products produced on such evaporators were of poor quality and exhibited a strong heat processed flavor. 

DISTILLATION A heat-dependent process used to produce alcoholic beverages, such as whiskey, rum, and vodka. In this process, a fermented mash (of grains, vegetables, or fruits) is heated in a boiler, causing the alcohol to evaporate. The alcohol vapors are then collected and cooled in a condenser to produce the beverage. 

The RO potentialities as a concentration technique to remove water from fruit juices for the production of high-quality fruit-juice concentrate are well known [24], The most relevant advantages of the RO process over traditional evaporation are in the reduced thermal damage of the product, increase of aroma retention, and lower energy consumption, since the process is carried out at low temperature. 

Crystallization can be used to remove solvent from a liquid solution. For example, concentration of fruit juice requires the separation of solvent (water) from the natural juice. The common procedure is evaporation, but the derived juices may lose flavor components or undergo thermal degradation during the evaporative process. In freeze concentration, the solvent is crystallized (frozen) in relatively pure form to leave behind a solution with a higher solute concentration than the original mixture. Significant advantages in product taste have been observed in the application of this process to concentrations of various types of fruit juice. 

Concentration of fruit juices should not result in marked loss of ascorbic acid if the pressed juice is deaerated and and evaporated at low temperatures (100). Ascorbic acid retentions in excess of 90% have been reported for concentration and freezing processes (38,101) and can be expected for freeze concentration processes (100). 

Crystallization is one of the oldest and also one of the most important processes applied to chemical products. It is one of the oldest, indeed perhaps the second oldest, since it can in many cases be brought about by the simplest of means, concentration due to natural evaporation. Concentration is probably the oldest chemical process known to man since it occurs naturally in the cases of natural solutions, e.g.y sea water in shallow rock pools, or in drying the juices of ripened fruits. Crystallization must be regarded as the second oldest chemical process as being the direct result of concentration. It may be contended that solution should be given first place for age, but it seems clear that this could only have been a man-controlled process after there were crystals prepared from natural solutions. 

The aroma of citrus fruit is a speciality. It consists of the so-called water phase and the oil phase. Citrus juices contain small amounts of volatile oils (0.03-0.06%). During processing there is always a small amount of peel oil that gets into the juice. Also the juice contains a small amount of oil, called juice oil. During evaporation these oils get into the aroma where they create the so-called oil phase. This oil has a very special aroma and is different from the peel oil by analysis (gas chromatography) as well as flavour. Oil and water phase are kept separately and added back to the juice according to individual requirements. Properly applied, the oil phase imparts the special fresh note to the juice which cannot be achieved by adding the water phase only. 

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