Citrus Juices Processing Technology

Citrus Industry has developed in different parts of the world with different characteristics according to citrus species available for processing in specific areas. Ina any case, there are some basic operations that are common to all citrus processing plant regardless location, size and specific processing technology. These operations are: 

  • Fruit unloading
  • Juice and oil recovery
  • Juice processing
  • By-products recovery
  • Wastes disposal
Juice and oil can be recovered with different systems; the most popular is FMC's one (nowaday JBT Foodtech), In-Line extractors. 

About 50 % of extractors installed in USA are FMC,, whilst in Brazil, Argentina and Israel this is the only system used. In-Line are popular also in Italy and Spain and worldwide. The unique characteristic of FMC system is that is only machinery able to process fruits without a preliminary cutting fruits in two halves. In-Line extractors treat 3, 5 or 8 pieces of fruit for each cycle; upper cups, assembled on a solid bar, move up and down through a cams transmission system, while lower cups are fixed on machinery's bridge. All cups are made by "fingers" that criss-cross when upper cups go down towards lower cups. Extractors have channels hopper where fruit arrive through an inclined feed belt; a cams system casts fruits into lower cups and lower cups start to descend; in this way, fruits start to be pressed against circular knives that stay at the bottom of lower cups and helded on top of strainer tubes that work as juice pre-finishers. Descending action cuts a plug of peeland when "fingers" criss-cross all inner part of fruit is forced downwards through strainer tube; juice passes in the juice manifold; peel do not come in contact with the juice. The pressure of upper cup and a restrictor in the unperfored lower part of orifice tube, force juice to flow through the holed part of strainer tube in the juice manifold, which is completely closed. In the same time, strainer moves upwards, pressing segments and forcing residue juice to go out through the strainer; pulp, seeds and rags are ejected from bottom end of orifice tube. Extraction cycle is complete when orifice tube gets upper end of strainer tube.  With "In-Line" extractors both juice yield and quality are very good; data change according restrictor's holes size, with peel clearance, and according to the height that orifice tube gets within strainer. In-Line extractors, also recover essential oil in the same time of juicing; in fact "cup's "finger" cut peel in stripes and press it causing oil stream out; oil is collected by a water spray as an emulsion; this emulsion is collected in a screw-conveyor and goes into a finisher to remove suspended solids prior to go to separators. In few words, with FMC systems, fruits are separated in four streams : Juice, peels, cores and oil emulsion.  
The only small defect of FMC system is linked with the fact that oil contained in the peel plug gets into the juice, lowering its quality; for this reason, FMC has available modified sets for obtaini a really very high quality juice (Premium Juice) that are characterized by cups with different shape, strainer tube with truncated cone shape, smaller knives. All is done to decrease plug size and lowering extraction pressure; the final result is a juice that is extremely close to an home made one. To complete overview, we must remember that FMC system needs a preventive size calibration of the fruit. 

Brown extractors, produced by Automatic Machinery Corporation, are base on a completely different principle; oils is recovered witha machinery (BOE) wich remember a fruit washer that instead of brushes uses cylinders covered with spikes; so whole fruits undergo to many bites to free oil thatis collected in form of emulsion with water.With respect to juice recovery, fruits are sliced in half; the halves are oriented and picked up by synthetic rubber cups mounted on tracks, The positioning of the cups permits precise programming of the approach of the reamer into the fruit. The plastic serrated reamers, situated on a turntable mounted on a vertical plane, can be made to penetrate the fruit rapidly at first and then more slowly as the point of maximum penetration is reached. Juice collects in the machine and is conveyed to finishers, while the peel is diverted to the waste conveyor. Juice yield is good and quality is excellent. 

Pelatrice - Rotary Press system is used basically in Italy and Spain. This system do not need a preliminary fruit size calibration before juicing. First of all oil is recovered, by passing fruits through a grating system made by stainless steel cylinders and screw conveyors having surface like rawhide, under a water spraying; deoiled fruits then go in the rotary press where they are sliced in half and the two halves are  pressed against a fixed sieve by two contra-rotating steel cylinders. It is possible to control juicing pressure by adjusting the gap between sieve and cylinders, but juice quality and yield are lower respect to FMC or Brown systems; in fact may happen to have bigger fruits that are over-extracted while smaller fruits will be under-extracted. In the first of the two case some peel components are transferred into the juice, lowering the quality, while in the second case is the yield that is affected.   

Tagliabirillatrice - Sfumatrice system is another typically Italian system; in this system first, is recovered the juice and , then, the oil. Fruits arrive to tagliabirillatrice through vibrating hopper, are sliced in half and the two halved fall in cups that hold them while plastic reamers extract the juice. The system is very close to Brown system but the practical mechanic actuation is completely different. Extraction pressure is adjustable, but reamers speed is fixed. Juice quality is really excellent but machinery capacity is small.  Peels after juicing, go in the sfumatrice that extracts the oil; its quality is really excellent, and in fact sfumatrice lemon oil is the only used in perfumery, on the other side yields are lower that other systems. We think that properly improving this technique may result in a very good system for fresh orange juice production or for very good quality lemon juice (e.g. a cut-back one) even if in this case will be necessary to install systems for recovering the oil lost by sfumatrici.  
Raw juice contains a large amount of pulp and needs to be refined; this is usually made through finishers. Some of them are based on paddle principle, other on screw system, but, in any case, all them reject cells and reduce pulp content up about 10 % 

After juice and oil recoveries are complete, juice processing is different according plant size, market shares, geographical locations of citrus plants. There is no doubt that most part of orange juice, lemon, juice, grapefruit juice is pasteurized and concentrated, but, mainly in Italy and Israel juice is still further refined up to 0,5 % pulp content to be suitable for soft drinks applications. Juice processing lines are usually made by coupling in series dekanters and vertical clarifiers; dekanters take away mainly the coarse pulp and facilitate the following work of clarifiers that fix final pulp content to desired level. All this is necessary because soft drinks customer do not like to see sediment at the bottles bottom. In soft drinks products are also important organoleptic characteristics, intended, mainly, as color intensity and cloudiness properties; opposite to juices, freshness and taste are less important based on dilution in soft drink and flavors addition, whilst stability is of top importance. After finishing, juice is pasteurized in tubular or plate heat exchangers with heat recovery. 
Citrus juices undergo to qualitative degradations if maintained, for more of a short time to room temperature, cause to  enzymatic and microbiological activities. Problems are, clarification, separation, concentrates gelation and microbial fermentation. All those problems are cancelled by pasteurization, that however, due to thermal sensitivity of citrus juices induces flavor variations and browning reactions. So, pasteurization needs to be optimized. Treatments usually are made using temperatures between 90 and 95°C for times ranging between 15 and 60 seconds.

Heat exchangers needs to be designed to support pulp; usually are tubular or plate exchangers with heat recovery using steam or, preferably, hot water as heating media. Due to pH of citrus juices there is no harm of developments of pathogenic microbe; in citrus juices can develop yeast, moulds and lactobacillus that may impart a bad butter flavor to the juice due diacetyl as end product of their metabolism.  Common yeasts are Saccharomyces and Candida; heat resistance of yeasts and moulds is lower respect to Pectinesterase one. Moulds presence is, usually, linked to post-pasteurization causes.  

After pasteurization, juice is, if necessary, debittered and is delivered to evaporators that eliminate water with enormous money savings in storage and transport costs. Frozen Concentrated Orange Juice (FCOJ) is surely a world "commodity". Brazil is leading producing country with more than 14 million MT of oranges and an output of more than 1 million MT of 65°Bx FCOJ. USA keep the second place with about 740.000 MT of concentrate, but we have to remember that in the States there is an enormous production of  fresh and Not From Concentrated (NFC) orange juice. Juice evaporators are, surely, machinery with higher technology in Citrus Industry and today are only distant relatives of simple machines of the beginning, when "forced circulation" evaporators were used. At that time a centrifugal pump was pumping juice through an heat exchanger where a small part of the water was evaporated at each recycle; liquid and vapors were separated in large cameras.  Processing temperature was of about 50°C for a long time. Thereafter falling film evaporators were developed, and product quality was heavily improved;   those evaporators were made by stainless steel cylinders approximately of 90 cm of diameter in which juice were sprayed against inner walls surface; on the other side there was hot water; evaporated water was transported upwards by steam jets and was condensed by a barometric condenser. Will to obtain better quality products was the real engine for developments of citrus evaporators. In forties, Mojonnier brothers invented their low temperature evaporator: It was a falling film evaporator that was using as heating media hot gas arising from a refrigerant in a heat pump cycle; in other words, hot gases were supplying heat to a falling film heat exchanger while liquid was condensing water vapor in side-exchangers. Juice film and vapors had the same direction. In the same period, were built first specimen of multi-effect machinery. In the sixties became clear that working at relatively low temperature for a long time was qualitatively less convenient of using high temperatures for a short time. 

Was Ralph Cook to invent the first evaporato based on this principle and he named it  T.A.S.T.E. (Thermally Accelerated Short Time Evaporator). This evaporators are able also to pasteurize the juice inactivating also the natural enzymes. In TASTE evaporators, juice is pumped through a series of interstage preheaters in which temperature is increased through heat transfer from vapors deriving from previous effect. The first preheater uses live steam and brings the juice to the temperature foreseen for first effect inlet. This preheater is able to supply a temperature - time profile adequate to inactivate PE and microbiologically stabilize the product. At every stage feed flashes through distribution cones and is evaporated in the tube - nest. Liquid and vapor go out at the bottom of tube - nest and are separated in cyclone - separators sided to tube - nests. Vapors go to next efect and are used as heaters to continue with evaporation process. Every effect is designed in such a way to obtain about the same amount of evaporation. Obviously, increasing concentration and lowering the temperature, viscosity increases causing a reduction of heat transfer rate.  This means higher exchange surface to balance heat flow from previous effect and is the reason why first effects require just one stage, while final are multistage. 

Concentrated juice coming from last stage is addressed to  a "flash cooler" where it undergoes to an adiabatic expansion, increasing its concentration and, in the same time, decreasing its temperature up to 5 -10°C. Most TASTE work with four effects and six stages; some others use seven effects and eight stages, the new ones are designed with five effects. Evaporation capacity varies in a extremely large range from 5.000 to 400.000 lbs/h of evaporated water. 
Other evaporators that we can mention are APV and Alfa-Laval plate - evaporators, Schmidt Sigmastar Evaporators and TVR Wiegand evaporators.