The fruit is directed to suitable fruit extracting systems for juice recovery. In the case of citrus juices two of the best known juice extractors were mentioned above. While squeezing citrus fruit, undesirable peel oil can easily get into the juice. To avoid this, some extractor systems are eliminating and collecting the peel oil before the juice is extracted. This is achieved by rasping and pricking the peel. The resulting oil raspings are spray washed off the peel and conveyed to a press where the oil/water mixture is separated from the solids to recover as much oil as possible. The oil/water mixture is separated in a two step centrifugation process producing the so-called cold pressed oil. Only after the oil is recovered from the peel the juice is extracted from the fruit in the extractor. This process applies to the BROWN (1) extractor system and those of other extractor manufacturers (e.g. BERTUZZI (4), INDELICATO (5), SPECIALE (6)).
Only the FMC extractor (see Figure 3.9-3.10) and recently, some similar machines from FOMESA (7) and OIC (8) allow a simultaneous collection of rasped peel for oil recovery and juice in separate streams. The juice passes from the extractor to a so-called finisher to remove the coarse pulp particles. Then the juice can be bottled as fresh juice or it can be used for the production of juice concentrate. If necessary, the pulp content of the juice can be further reduced by centrifugation, using so-called de-sludger type centrifuges (ALFA LAVAL and TETRA PAK (9), WESTFALIA SEPARATOR (10), etc.).
Fig. 3.9: The FMC Citrus Juice Extractor
Juice from fruit which is mashed for juice extraction, e.g. apples, pears, pineapples, grapes, cherries, is produced by pressing.
The structure of the mash varies according to the fruit type. A mash with a high fiber content is pressed more easily than mash from very soft fruit. Pineapples for example can be pressed easily with screw presses, whereas special presses have been developed for softer fruit, like apples. For many years, the BUCHER (11) press was commonly used for processing apples. The BUCHER HP press is a hydraulic press working in cycles. The mash is filled into the press and under pressure the juice drains through flexible hose-like drainage filter elements. Once the extraction is completed the pomace is discharged and the process starts over again. Yield and quality of the juice are excellent and the system has proven to operate reliably with many fruits .
Another type of press, the continuous beltpress, which was originally used for drying sewage sludge, has been re-designed for fruit processing. Belt presses for the food industry are available from various manufacturers (AMOS (12), BELLMER (13), DIEMME (14), FLOTTWEG (15), KLEIN (16), etc.) [2-5]. The working principle is to press the mash between two sieve belts which continuously pass around cylindrical rollers. At the beginning of the pressing operation the diameter of the rollers is large and the applied pressure is low. As the pressing operation progresses the rollers become smaller and the pressure increases. The tension of the belt and the pressure around the rollers can be adjusted pneumatically and the belt speed can be varied as well. The pressed pomace is removed from the belts by means of plastic scrapers and/ or by rotating brushes and the belts are cleaned with high pressure water on the return
1 Upper Cutter: Cuts a plug in the top of the citrus to permit the separation of the peel from the internal portions of the fruit. Upper / Lower Cup: Supports the exterior of the citrus throughout the squeeze cycle to prevent bursting.
Lower Cutter: Cuts a plug in the bottom of the citrus to allow the internal portions of the fruit access to the prefinisher tube. Prefinisher Tube: Separates, based on particle size, the internal elements of the citrus. Juice Manifold: Collects juice and juice sacs.
Orifice Tube: Generates pressure inside the prefinisher tube and collects and dis charges membrane and seeds.
2 In this early phase of the extraction cycle, the upper cup moves downward to cause pressure on the citrus so that the top and bottom plugs begin to be cut.
3 As the extractor cycle continues, pressure increases on the citrus causing the internal portions to be forced through the bottom of the fruit and into the prefinisher tube. The peel is now being discharged between the upper cup and cutter.
4 Upon completion of the extraction cycle the internal portions of the citrus are located in the prefinisher tube. At this time, the orifice tube moves upward, placing pressure on the contents of the prefinisher tube. This causes the juice and the juice sacs, due to their small particle size, to flow through the holes of the prefinisher tube and into the juice manifold. Particles larger than the holes in the prefinisher tube are forced through an opening in the orifice tube and discharged out the bottom.
Fig. 3.10: The FMC Citrus Juice Extractor Principle to the mash feed location. The juice coming from the press could contain coarse fruit particles which are removed by an additional simple screening device. When the recovered juice is to be bottled as natural cloudy juice or to be converted into cloudy concentrate it is advisable to remove the insoluble solids by centrifugation. This will avoid formation of bottom pulp in the bottle and it will also aid the concentration process in the evaporator.
The main advantage of this press is the short duration of the entire pressing operation which only lasts a few minutes from mashing the fruit to dejuicing.
The one-sieve belt press is a new development. Also here the belt passes around several cylindrical rollers of different diameters in order to increase the pressure during the pressing operation and to achieve a high yield.
To increase the yield and improve the pressability of the mash it is recommended to treat the mash with enzymes. Specific enzymes, referred to as "press enzymes", have been developed by leading enzyme manufacturers. In order to increase the yield of juice from the mash another specific enzyme for the so-called "mash liquification" was developed and tested.
When producing concentrates instead of fresh juice the juice yield from the mash can be increased by washing the pomace from the first pressing with water (e.g. 1:1) and repeating the pressing operation to recover additional soluble juice solids. Especially designed water extraction systems also result in yield increases (see below). The soluble solids recovered from washing of the pomace can be added to the juice. This procedure is not suitable for fresh juice production but only when processing concentrates due to the dilution with water and the lower soluble solids content in the water extracted juice.
When processing apples, the recovery of juice solids can also be achieved by continuous countercurrent extraction with water. These extraction systems were derived from the extraction of sugar beets in the sugar industry and they work either as hot or as cold extraction.
The extractors work well on freshly harvested, early fruit which has a firm structure. However, as the degree of maturity of the fruit progresses and as the fruit becomes softer, the operation becomes more and more difficult due to the softness of the mash and the decreasing water permeability of the mash layer. Water extraction systems are more and more replaced by the simpler fruit presses.
A similar procedure for the recovery of juice solids is applied in citrus processing. The dejuiced pulp coming from the juice finisher is countercurrently extracted with water in several processing steps. One extraction step consists of a mixing screw and a finisher. In the mixing screw the pulp is mixed with the extraction liquid and in the finisher the liquid is separated from the extracted pulp solids. The liquid is run countercurrently to the pulp from stage to stage. The more extraction steps are built into the process the better the recovery of soluble juice solids from the pulp and the higher the concentration of the recovered liquid. These so-called (soluble) pulp wash solids can be added back to the juice when processing the concentrate.
Another possibility is to produce concentrate from the recovered juice solids as such, so-called "pulp wash concentrate", or "OWP" (Orange Wash Pulp) or "WESO" (Water Extracted Solids) respectively.
The pulp wash liquid from citrus fruit contains a higher amount of pectin than the single strength juice from the juice extractors. In most cases it must be treated enzymatically to achieve a sufficiently high concentration in the evaporator. In order to aid the concentration it is also commonly practised to centrifuge the liquid prior to evaporation to remove some or most of the insoluble solids from the liquid.
The taste of these products is usually clean but flat and less aromatic than normal juice. A result of the higher pectin content, pulp wash products usually have an extremely good turbidity and cloud stability which makes them well suited for the production of drinks with low juice content.
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