7 De hyd ration of Fruits The United States is by far the largest producer of dried fruits, raisins and prunes being the most important tonnage-wise, with figs, apples, apricots, peaches and pears following in order of tonnage produced. Other countries with a substantial export trade in dried fruits are Greece (producing 90 percent of the world's currant supply), Iran, Turkey, Portugal, Iraq, Algeria, Australia, Argentina, Egypt and South Africa. Of the above, the Middle East countries are particularly important in the drying of figs and dates. Sun drying has always been important as a drying technique for fruit and it is still carried on extensively, other than for apples, prunes and some types ofraisin. Withcut fruits, particularlyapricots,pearsand peaches, it has long been considered that using solar energy to remove the water from these fruits produces a superior quality to that obtained by artificial drying, and in a dry harvesting season there are cost advantages, which have been critically pin-pointed since the fuel crisis in the 70's. However, reliance on sun drying brings the risk of inclement weather at harvest time and the difficulty of maintaining a high degree of sanitation in the process. Consequently processors have made considerable efforts to improve quality in artificial drying, particularly with cut fruits, (apricots, peaches and pears) by introducing the Dry-Blanch-Dry method, to which detailed reference is made in the process data on apricots which follows. I69 This method has been devised by Lazar, Barta and Smith of the Western Regional Research Laboratory, US Department of Agriculture, Albany, California, where promising tests have been made on apricots, peaches, pears and raisins. Apricots, particularly, responded well to this method, the dried fruit retaining a bright translucent colour instead of the dull red-orange of the sun dried product. The best results were obtained by reducing the blanching temperature to under 100°C at the 50 percent weight reduction point the primary drying. Such a system was also effective with raisins, whichsuffer fromsplittingof skinswitha 100°C blanch,and this was eliminated by a temperature reduction to 92°C. Sulphiting The use of sulphur houses was ordinarily, but not necessarily, exclusively associated with sun drying methods, and sulphite dipping with mechanical drying. A sulphuring house is always erected away from the main factory building. The fruit is spread on trays which are racked on trolleys in a similar manner to that used in tunnel drying. The trolleys are pushed into the sulphuring shed, which is fitted with a sulphur burner at the bottom end, with adequate venting to atmosphere, either by natural draught or by fan, through the roof. 2 to 3kg of sulphur are burnt for each ton of fruit treated, and the exposure time is varied according to the absorption characteristics of the fruit. The latter must be tested regularly but, as a guide, the concentration of SO, in thesulphur shed should be maintained at about 2 percent. Residual SO, in the dried fruit will range from 1500 to 2000ppm. An exception to the use of sulphite can be exercised with Thompson Seedless grapes for the production of 'natural' raisins instead of the more common 'golden-bleach' raisins which contain levels of SO, up to 2000ppm and are mostly artificially dried. Processing All the fruit processing described in this chapter except currants and peaches relates to artificial drying in either Conveyor Band, Tunnel or Stove Dryers,and whilst the Dry-Blanch-Dry method is prescribed for Apricots on the basis of the author's trials, it could equally be used for Pears and Peaches, Apple Rings and natural Raisins. Apples (Rings and Flakes) (1) Flow Sheet Feed to Line I70 I Washing I Grading I Peeling-Coring I Trimming I Sulphiting I Cutting I Re-sulphi ting I Drying I Inspection I Packing (2) Varieties USA Baldwin, Delicious, Jonathan, Permian, Winesap UK Bramley Seedling (Cooking variety) Left: A Fruit Washer produced by the Bead Engineering Company 171 Eastern Europe: Red Delicious, Golden Delicious, Jonathan Turkey: Arap Kisa (Cooking variety), Delicious Note: The more acid cooking varieties soften more readily when rehydrated, which can be an advantage. However, in practice, more dessert types are generally processed. This is mainly on account of their more symmetrical shape, which makes mechanical peeling easier and less wasteful. Of the dessert varieties listed above, Delicious, both red and golden types, are the least suitable for processing, on account of their tendency to break down in preparation and low acidity. However, they are grown more widely in America and Europe than almost any other dessert apple, and may be used in seasons when there is a shortage of apples of higher acidity. (3) Product Handling The apples are brought to the plant in field boxes and, if pesticides have been used in the orchards, it is necessary to tip the fruit into a washing tank, or subject it to water sprays. It is essential to grade the apples, and the more accurately this is done, the less waste will occur in peeling and trimming. The following table gives the approximate number of each grade of apples (by diameter) per kilogram. Grading Diameter Weight per fruit No. per kg No. per tonne 50 70 14.286 14,286 60 85 11.765 11,765 70 115 8.696 8,696 80 155 6.452 6,452 90 210 4.762 4,762 in mm. in g Subject to slight variation as between varieties. Peeling and Coring There are three options: (a) Hand peeling ($)Steam flash peel (c) Mechanical peeling With hand peeling a substantial labour force will be required,and this may only be viable with a small scale operation. With careful control and skilled operators, peeling losses can be as low as 33-35 percent. Flash steam peeling can be carried out in a short immersion steam peeler operating at 17atm, and normally 15 seconds exposure time is I72 necessary. The apples then pass through a skin eliminator with powerful waterjets. Losses by this method vary from 45 to 47 percent for medium sized apples, including coring losses. Mechanical peeling can be carried out by a battery of semi automatic ‘Pease’ peeling and coring machines. Each machine has 4 paring and coring heads, and is fed by one operator at a rate of 80 apples per minute at 100 percent efficiency but, in practice, 75 percent of the manufacturer‘s rated throughput is more realistic. More manual trimming is often required after the machines, and 50 percent losses are usual. The following table gives the theoretical and proven outputs (factory test) of one 4 head unit. Diameter Throughput/hour Throughput/hour Throughput per in mm @ 100% efficiency @ 75% efficiency 8 hours 50 336 252 201 6 60 408 306 2448 70 552 414 331 2 80 744 558 4464 90 1008 756 6048 kg kg kg From the above factory figures, based on an actual day’s production, 4 units produced 6.5 tonnes of prepared apples averaging 70mm in diameter. 30 trimmers were employed on the inspection belt. A better type of mechanical peeler with automatic feed is available from Atlas-Pacific. This will handle 110 apples per minute (at 85 percent efficiency) or 700kg per hour of 80mm apples. Peeling losses are claimed to be 35-40 percent, and with regular shaped apples of good quality, few trimmers are required -approximately one third of the number needed with 4 semi automatic units. The principle of mechanical peeling and coring is that the apples are offered up to, and impaled on a rotating spindle and a spring-loaded ’floating’ peeling knife follows the contour of the rotating fruit, removing a narrow strip of peel. A circular coring knife then lifts in an arc in a simultaneous movement and removes the stem, calyx and seed cells in one operation. The peeled and cored apple is then mechanically ejected from the spindle down a chute and on toa discharge conveyor which delivers it to the inspection and trimming conveyor. As soon as the apple is peeled and trimmed it must be submerged in either a 1.5 percent salt solution or sulphite solution to prevent browning and oxidisation. This is most conveniently done in a flume which delivers I73 the fruit to the cutting machines. The fluming solution is recycled from a collecting tankat thepointwheretheapplesareseparatedout from the flume liquor, and from here they are conveyed to the cutters. Cutting The method of cutting will depend on whether ‘evaporated’ rings, or segments are being processed - or whether the apple is going to be dried down to low moisture (4 percent) as flakes. For the former a slicing machine will be required - either a CC model as described in Chapter 3, or a heavy duty slicer; if segments are required, a machine with radial knives is used, the number of knives depending on the size of segment required and the size of the fruit. The apples are held in position by a rod through the core opening. With slices it is desirable, as far as possible, to use a machine which cuts at right angles to the centre axis. A slice of TO-12mm in thickness is customary. Too thick a slice will prolong drying. If flakes are required, the apples are fed into a G type dicer and cut in 1Omm by lOmm by 2mm pieces. Re-Sulphi f ing The Rings or Flakes are passed through a sulphite bath to bring the residual SO, level in the end-product up to 1500ppm (2000ppm is the legal maximum permitted. Dewatering Excess water is removed with as little delay as possible, otherwise leaching losses will occur. A leaching loss of 5 percent can occur with an immersion time of one minute when fluming and sulphiting. These losses of totalsugars and other soluble flavour constituents will reduce the weight of the final product, as of course the percentage of total solids in the prepared material as it enters the drying process is the whole key to viable production. Once the apples are peeled, therefore, they should not in any circumstances be stored in surge hoppers or tanks awaiting further handling. (4)Drying Conveyor Band, Stove or Tunnel Dryers, scaled to throughput. Inlet temperatures not to exceed 70°C in first zone, 50°C in last zone. Dry Rings and Segments down to 20-22% moisture Dry Flakes down to 4% moisture Raw moisture is assumed to be approximately 88%. Overall ratio 13:l and Drying ratio 7:1 for Apple Flakes. Overall ratio 10.5:l and Drying ratio 5.3:l for Rings. I74 (5) Storage for up to 8 months. Apricot (Halves) (1) Flow-sheet Freshapplesmaybestored inchillroomsat-1 "C to+3"Cat85-90% RH Feeding to line I Dip (whole) in SO, + citric acid I Pitting I Dip (Caps) in SO, + citric acid I First Stage Drying I Blanching I Second Stage Drying I Inspection I Packing (2) Varieties (recommended) Blenheim. (USA) Matalya (Middle East) (3) Product Handling Feeding to line is by bulk feeder, whence the fruit is elevated into a sulphitedip tankholdinga solutionof 2percent sodium metabisulphiteplus 0.5 percent citric acid, duration 5 minutes. Fruit is dewatered on a stainless screen and fed on to an inspection conveyor for pitting by hand, or alternatively elevated into an apricot pitting machine. Manually fed machines are also available from FMC. Caps are elevated into a second sulphiting tank with the same concentration as the initial dip, duration 1 1/2 minutes, followed by dewatering. First stage drying is carried out on trays (stainless mesh) the halves being in 'cup-up' position, ie, cut surface upwards. Trays are transferred to a steam blancher (belt-type) with transit time I75 giving exposure to steam for 4 to 5 minutes. Trays are transferred to a secondary dryer and in the final stage caps are reversed to 'cup-down' position. This reversal can be effected mechanically. Bin Drying to achieve moisture equilibrium. Inspection and Packing. Inspection belts should always be fitted with permanent magnets and metal detectors (non ferrous). (4) Drying Stove or Tunnel Dryers should be used in view of the lengthy drying cycle and the necessity of primary and secondary drying as separate operations. First stage drying is for 2 1 /2 - 3 hours with tray loading at lOkg per sq m. In this stage the weight reduction is 50% of the feed weight. Inlet temperature 71 "C cup-up position. The second stage drying is for 5 1 /2 - 7 hours at 71 "C reducing to 65°C half-way through the cycle at which stage the cups are reversed to cup-down position. Bin Conditioning at 49-50°C to achieve moisture equilibrium at 20-22%. Overall ratio: 8 : 1 Drying down ratio. 7.46 : 1. (5) Equipment Mechanical and manual apricot pitters and cup-up and cup-down machines can be supplied by Food Machinery Corp of San Jose, Cal. or FBR SrL of 43100 Parma, Italy. Banana Flakes (1) Flow-sheet Feeding to line I Hand Peeling I Buffer storage in SO, Dewatering I Pulping I Pasteurisation I I I7I Mixing I Homogenizing I Drying I Packing Gros Michel Cavendish (2) Varieties (3) Product Handling Single fruits are fed to the line, the stripping from 'hands' being handled outside the factory in sheds or at the farms, peeling and trimming off pith and dark flesh on a 'merry-go-round' conveyor. The peeled whole fruit is collected in buffer storage tanks (two required) with SO, solution 0.05-0.1 percent for up to an hour. The fruit is dewatered and fed into a comminuting machine with a 0.5mm mesh screen to remove the seeds and fibre. Use an Urschel Comitrol machine with homogenising head SH 200084N (capacity 2000kg per hr) Feed pump into an auger-type steam blancher and pasteurise for 8 to 10 minutes in live steam. Collect pulp in a U-Trough mixer. Add SO, solution,reducing original total solids from 25 to about 20 percent. Level of SO, will be regulated to arrive at a residual SO, level in the end-product of 150ppm at the discharge point. Feed the pulp into a colloid mill for secondary homogenization. Elevate by auger feed to a drum dryer, with drum temperature of 171 "C drying to 4 percent moisture. Inspect flakes on belt conveyor, with metal detectors (ferrous and non ferrous). Add up to 2 percent anticaking additive and pack in airtight cans (4) Drying should not exceed 93°C and the drum temperature 171°C. Ratio overall: 8:l Drying ratio: 4.4:l Final moistures of flakes is maximum 4% Currants and from grapes grown in the Aeghion-Patra and Korinthos region. Single drum dryer on which the maximum product temperature Almost 90 percent of the world's currant supply comes from Greece, The best quality currants are produced from the Vostizza grape I77 peculiar to this part of the Greek mainland. The fruit is grown sometimes on relatively small farms as well as on the larger estate farms, and the whole crop is contracted to a handful of merchants, in Patra mainly, and these process the crop after the farmers deliver it to the storage and processing factories. Currants are not produced,in quantity to the author’s knowledge, outside of Greece, other than small tonnages in Australia and South Africa, therefore the methods described come from knowledge acquired on visits to the Patra region. All the fruit is sun dried and this operation is carried out by two methods: (a) by stripping the grapes from the vine and laying them on concrete floors outside the farmsteads, protecting them by sheets of paper underneath and with gauze or nylon net on the top to protect them from birds and other predators, and also from the rays of direct sunlight at the hottest time of the day. (b) by taking off the bunches and hanging them on the shoots of the vine to dry under the protection of the foliage. This is labour intensive but is practised by the smaller growers, or others who have abundant cheap labour. This method produces a premium quality currant and commands a higher price from the proccssor. The fruit is dried down to about 14 percent moisture in the farm yards, and is then stripped from the stems to a tolerancc of 6 percent waste matter before delivery to the processing factories. Secondary Processing The dried fruit is assessed for quality on delivery to the warehouses, and is piled in heaps on the concrete floors, sometimes up to three or four metres deep. The currants, as delivered, are then prc-riddled to remove stalks, dirt, stones and other extraneous matter, and are aspirated in a second stage of dry cleaning. They then pass on to a ’breaking’ machine, which separates the fruit where it has becomc compacted. Fruit then goes to grading machines which separate it into three sizes -small, standard and ’jumbo’. The first grade is set aside for catering outlets, the standard for retail and other premium outlets, and the over-size fruit normally go as a by-product for the production of alcohol. The separate grades are washed by fluming over riffle plates, and pass to a spin drying machine which removes the exccss water centrifugally. Fruit is then packed in lined wooden boxes, or cartons, which finally go into I78 a fumigation shed for methyl-bromide treatment. This has to be repeated at regular intervals during storage, and before shipment. The process has not changed radically over many years, and at first sight would appear to be primitive. However, with the demands for rising quality standards by the importers and users of dried fruit, it is almost universal practice for the fruit to be re-selected, washed and re-dried when it arrives in the buyers’ premises. The number of dried hit importers in the United Kingdom is relatively small but they arebig companies with excellent processing facilities and, being ‘brand conscious’, they invariably market a high quality and hygienic product. This applies to importers in Europe and elsewhere equally rigidly. Paw Paw (Carica Papaya) (1) Flow-Sheet Feed to Line I Washing I Inspec tion I Peeling I Quartering I De-seeding I Inspection I Cutting I Drying I Conditioning I Inspection I Packing (2) Varieties Indigenous I79 (3) Product Handling Whole fruit is washed and inspected before peeling, quartering and de-seeding; the latter will most probably be done manually. Thebest type of belt for the latter processes is a stainless Sandvik-type conveyor rather than a rubber belt, for reasons of hygiene. The quartered fruit is then cut into small segments or dice by a Model C dicer set for 6 by 6 by 6mm cubes upwards to 13mm After drying and conditioning the material is inspected, screened and packed. (4) Drying Stove dryers are normally used with an inlet temperature of 88°C for 1 hour, reducing to 65°C in the second and final stages. End moisture should be 6%. Raw moisture 92-94%. Peaches (1) Flow Sheet Primary Processing Feed to Line I Grading I Washing I Dewatering I Pitting/Halving I Sulphuring I Drying I Sweating Secondary Processing Inspection I Washing I Sulphuring I Grading I80 Right: A manual apricot pitter I Inspection I Packing (2) Varieties Freestone Peaches should be used - not Clingstone. The main variety in California is Muir, followed by Rochester, Hale's Early, and Peregrine. There are many Mediterranean varieties which are equally suitable. (3) Product Handling Fruit is harvested in fully ripe condition and must be handled with care to avoid bruising. The peaches are first graded and inspected toremove damaged or diseased fruit and then washed to remove dirt and skin 'fuzz'. After washing, the fruit is dewatered. Freestone peaches do not require peeling in the manner that Clingstones are handled for canning, ie, lye dipping. Pitting and halving may be done by hand for a small operation but for larger throughputs machine pitting and halving is essential. l 8 l The caps are then placed on wooden trays, cap uppermost in a single layer, and the trays are racked on to trolleys and placed in the sulphuring shed. 2.5kg of sulphur is burned for each tonne of fruit loaded in the shed. The exposure time is 4 to 5 hours or such time as is required to obtain a residual SO, level of 2000 to 2500ppm at the end of the cycle. The trays are stacked singly in the drying yard, on racks about 25 cm from the ground and exposed to the sun for 10-12 days, according to climatic conditions; the fruit is dried to about 18 percent moisture in this period. After sun-drying the fruit is transferred to curing or 'sweating' boxes to equalise the moisture. Alternatively, it may be spread out on a clean concrete floor and turned regularly. Any wet fruit is returned to the traysand spread on the racks again for further sun-drying. Secondary Processing After preliminary inspection of the halves, they are washed in a rotary reel washer torender the fruit pliable,and in the course of this washing about 10 percent moisture is re-absorbed. The fruit is finally spread on the sulphiting trays again and then returned to the sulphuring shed, where it is exposed to the burning sulphur for a further 4 hours. Final moisture is controlled at 22 - 25 percent. The fruit is graded again into six sizes determined by the diameter of the caps. (4) Drying The drying method described is sun-drying, as the drying cycle is so prolonged as to make artificial drying in tunnels too protracted. Experiments have been conducted, however, by the Agricultural Research Service of the US Department of Agriculture on drying by the DBD method (Dry-Blanch- Dry) with some success - using tunnel dryers. Whilst this method has been proposed for commercially drying apricots, based on the author's practical trials, no personally collated data on DBD is available, hence sun-drying only has been proposed. The US trials on DBD disclose the following information: Sulphiting Time 1st stage drying Blanch 2nd stage drying Product Analysis. Moisture SO, 3% S 0, Dip 8 mins 4.5hours 68'C 6mins 17 hrs 63 68'C 16 % llOOppm @1Oo"C The Research Institute reports that no commercial drying of peaches I82 by this method is currently being carried on at the time of the experiments but that the results were sufficiently encouraging to promote larger scale tests. Pineapple (1) Flow-Sheet Feed to line I Washing I Grading I Sizing-coring I Inspection I Slicing I Dicing: Segmenting, Sulphiting, Drying I Conditioning I Inspec tion I Packing (2) Varieties Smooth Cayenne (3) Product Handling Pineapples are usually processed in cans and on a large scale, involving high speed and highly specialised plant manufactured by two American Corporations, FMC of San Jose, Cal. and The Carter Co Inc. of Hawaii, the traditional home of pineapple canning. Evaporated pineapple is processed therefore on a much smaller scale. After washing, which should be carried out in a flood-type washing machine to avoid bruising, (probably a tomato washing and inspection line would be most suitable for a medium sized operation), the fruit is graded. Most hit will fall into the range 1.6 to 2kg (with crowns) and the crowns represent 16-20 percent of this weight. Diameter will range from 7.6 to 14cm and length from 18 to 22cm. Possibly the smaller fruit will be most economical I83 for drying and the operation would be more viable if it were combined with canning, where the larger diameter fruit could be diverted for this purpose. The standard high speed high capacity Honiron pineapple grader, made by the Carter company, has a capacity of up to 60 tons per hour; therefore, for a smaller operation, a simple fruit or vegetable grader would have to be adapted. Sizing and coring is usually carried out on a Honomach Ginaca machine set for a specific size and operating at 120 pineapples per minute. Alternatively, if small fruit are going to be used the Carter Co can offer a small Sizer-Corer to handle 7cm fruit at half the price of the Ginaca. After sizing and coring, which implies the removal of the skin and coring down the centre of the fruit, a cylinder of fruit is left, which passes on to a stainless steel conveyor belt for inspection and trimming if required. The trimmed cylinders are then conveyed into a pineapple slicer, thence to a Honiron segment cutter, which will produce dice, spears, titbits or chunks. This is a relatively small capacity machine but is probably relevant in context of a medium sized drying project. The comminuted pieces are then sulphited by immersion in a sulphiting tank, dewatered and passed to the dryer. After conditioning, the fruit is inspected screened and packed. (4) Drying For a medium sized operation, probably a double tray dryer or stove dryer is most suitable, and again a lower temperature is often used in the first stage - 63°C - finishing at 65°C - 68°C. This tends to prevent caramelisation of the sucrose in the fruit. Raw Moisture is about 85%. Moisture content in the end-product ranges from 15 to 18%. Drying ratio: 6:l Overall ratio depends on crown weight and sizing losses, which could be up to 50%. This would create an overall ratio of 12:l. (5) Equipment Suppliers Carter Co Inc 91-060 Hanua Street, Ewa Beach, Hawaii 96706. - or FMC International AG 1459 Coleman Avenue, Box 1178, San Jose, CA 95108 USA. Pears (1) Flow-Sheet Special pineapple plant: Maturing I i 84 Feed to Line I Grading I Washing I Inspection I Peeling-coring I Halving/Quartering I Inspection/Trimminlj I Sulphiting I Dewatering I Drying I Inspection I Packing (2) Varieties Williams Bon Chretien (Bartlett) (3)Product Handling Whilst William's are probably the best variety for processing they are somewhat difficult to produce for processing at the criticalstageof maturity, and it is almost impossible to pick off the tree and transfer to the factory at this stage, as in 2 to 3 days after ripening they soften and become flavourless and rapidly deteriorate. it is necessary, therefore to pick them green at a specific Maturometer reading, hold in store in boxes at 16" to 18°C in 85 percent humidity. They are tested daily with a Maturometer,and fed into the plant when exactly ripe for processing. Pears for dehydration should not be too large, as this would prolong the drying cycle. 50 to 60mm diameter is about the top limit for size, and 45mm the lowest calibration. The graded fruit is separated into two sizes, which are transferred separately into a fruit washer, then inspected for damaged or blemished pears. I85 The fruit is then conveyed into an Atlas Pacific Pear peeling, coring, and halving unit with waste conveyors. If required the fruit could be quartered instead of halved. Each Atlas unit requires one operator and handles 750 - 800kg per hr depending on the size of fruit. As there is an hydro- feed tank in the Atlas Pacific plant, the preliminary wash may not be thought necessary, and is therefore optional. The cut pears are then passed over an inspection belt for trimming so that any seed cells which may have been missed by the peeling plant, or any discoloured flesh are removed. The product is then sulphite dipped and dewatered. A sulphite solution vessel and stirrer are located alongside the applicator tank to make up the concentrated solution, which is metered in, to maintain the SO, level. Drying is by stove or tunnel dryer, as the cycle is 12-18 hours depending on piece size. Low drying temperatures must be observed in order to retain the cream colour of the pears. The dried halves or segments are inspected and packed in the same way as for apples and apricots. (4) Drying Tray loading is about lOkg per square metre. Inlet temperatureat the hot end should not exceed 65°C and 57°C at the cool end. Conditioning at 49°C to 50°C. Dry down to 20 - 22%. Raw moisture = 85%. Overall ratio = 10.5:l to 11:l Drying ratio = 5:l (5) Equipment Suppliers Complete pear peeling, coring and cutting plant: Atlas Pacific Engineering Co 67th and Hollis Street, Emeryville, CA 94608 USA. Maturometer (hand machine): FMC. Pear core trimmers: FMC (hand tool). Plums (Prunes) (1) Flow-Sheet (A)Drying (B) Processing I I Feed to Line Dry Screening I I Washing Grading I86 I I Inspection Holding I I Drying Blending I I Conditioning Stabilising I Dewatering I Sorting I Packing (2)Varieties Oregon-type Red Plums (3) Product Handling The plums are fed from a bulk feeder to the washing plant, which is usually a reel washer with a powerful water spray. If the fruit carries an exceptional amount of soil and extraneous matter a second flood wash may be necessary. The plums then pass over an inspection belt on which defective fruit and any remaining stalk or leaf are removed. They are then loaded on to drying trays for drying in a stove dryer or a twoor three pass tunnel dryer. As thcdrying cycle is 24- 36hr- occasionally up to 48hr for large fruit - this is the only type of dryer suitable. Drying tends to be uneven hence it is necessary to transfer the prunes on to tables for conditioning and here to remove any wet fruit for secondary drying. The prunes are then transferred into boxes to be held for what is described as 'processing'(B). The second flow-sheet describes this supplementary handling. Theprunesare passed througha dry reel tobreakdownany 'clumping'. They are then graded into sizes dictated by the count per kg weight. The largest fruit may be 55 per kg and the smallest 330 per kg. The local type of plum will dictate, by its average size, how many grades will be required to produce an acceptable presentation. To limit the number of grades, some blending of near equal sizes is done from the holding boxes of primary graded plums. Moisture is then stabiliscd by some rehydration in steam to arrive at 20-22 percent moisture, then dewatering. Where permitted by food laws a I87 spray of potassium sorbate solution is applied to give a residual level of A final inspection is given before packing in 14kg cartons. 400ppm. (4) Drying Inlet temperatures in the first zone should not exceed 75°C otherwise there may be some problem of fruit bursting. Drying temperatures reduce progressively to50”C in the finishing zone, and theend moisture is normally in the range 16 to 19%. In reprocessing the steam rehydration brings this up to the 20 to 22% referred to earlier. The dual process permits the initial drying to be done during the harvesting period, and the secondary processing is done out of season as the product is required for marketing. Raw moisture of plums is 83%. Drying ratio can be expected to be about 6:l Overall ratio will depend very much on the condition and size of the raw material but should fall between 8:l to 10:l. Raisins (Golden Bleached) The Thompson Seedless Grape is used mainly for the production of raisins, although Muscat and Sultinana grapes are processed in some localities. California is the major producer, with Greece, Australia and Turkey also being substantially involved. There are several methods of production, namely soda-oil or sodium hydroxidedip before sun-drying (California) rack-drying (Australia), natural sun-drying without pre-dip, sulphur bleach, and golden bleach. The soda dip involves immersing the fresh grapes in a 0.25 percent solution sodium hydroxide at a temperature at 94°C for a few seconds, then rinsing in cold water before sun-drying. The lye treatment removes the bloom and checks the skin to hasten drying. A second method used in Australia is to dip them in a solution of 0.3 percent lye, 0.5 percent potassium carbonate and 0.4 percent olive oil at 82°C for 2-3 seconds. This is not rinsed off before drying. For the last two to three days of drying, the fruit is placed in direct sunlight to effect a colour change from dull green to yellow or light brown. The process which follows, however, concerns the process for Golden Bleach Raisins in which the grapes are dried mechanically in a tunnel dryer. This type of dryer is rccommendcd in view of the long drying cycle of 24-25 hours. I88 (1) Flow-Sheet (Primary Process) Feed to Line I Inspection I Lye Dip I Washing I Tray Loading I Sulphuring I Drying I Fumigating in Sweat Boxes (Secondary Process) Feed to Line I Dry Screening I Stemming (1) I Screening I Aspiration (1) Stemming (2) I Aspiration (2) I Washing I Dewatering I Stemming (3) I Sorting I Packing I89 Fumigating (Flowline by Courtesy Van Arsdel, Copley and Morgan - Food Dehydration 1973) (2) Product Handling This is done in two stages Stage 1. Inspection. The grapes are inspected when fed to the line, and diseased and damaged fruit removed. In some instances, large bunches are broken down to smaller ones to facilitate quicker drying. Dipping. The grapes are dipped for 2-3 seconds in a lye bath (94°C) in a solution of 0.25 percent sodium hydroxide, then washed in cold water. Tray loading. In California the fruit is loaded on to wooden trays which are racked on to trucks and transferred to the sulphuring house. Sulphuring. The trucks are held in the sulphuring house for about 4 hours, exposed to the fumes of burning sulphur - 2kg of sulphur being used per tonne of grapes in the chamber. Drying. The trucks are then transferred to a tunnel dryer, where they remain until dried down to about 12 percent moisture. The trays are loaded 19kg per square metre, or 3 1 /2-41b per square foot. The inlet temperatures in the first tunnel must be kept low, otherwise SO, losses by heat will cause discolouration. 74°C should be adequate in the first stage, with a finishing temperature of 55°C. An SO, target of 2000ppm should be aimed at to maintain the bright colour desired. The dried fruit are then stored in ’sweat’ boxes until they are ready for secondary processing. During this period the boxes should be fumigated at two weekly intervals to kill any infestation, and the ‘sweating’ is merely a process of conditioning the fruit at ambient temperature and allowing it to reach equilibrium by moisture diffusion through the mass of product. The effect is similar to that in conditioning vegetables in bins after primary drying except in the case of fruit there is no heated air-flow and conditioning is natural at ambient temperature. Stage 2. The raisins are fed from the sweat boxes on to a rotary/aspirated screen to remove extraneous matter. Sfemming. They pass into a stemming machine which mechanically removes the raisins from the panicles by a strigging action. The fruit must notbe higher than 12 percent moisture,otherwise thestems will be too soggy I90 and may clog the machine. ScreeninglAspiration. This is a further cleaning operation to remove any trace of stem left behind by the previous operation. Stem Capping: Aspiration. Stem capping removes the small stem adhering to the individual raisins and these stems have to be removed by aspiration. If at any stage stemming proves to be difficult due to the residual moisture being slightly too high, some further rapid drying may be necessary in a stove or cabinet drying, at 50"- 55°C. for 3-4 hours. Washing. This is a rapid rinse to finally clean the fruit and will increase the moisture to maximum 17 percent. The raisins are then dewatered. Inspection. At this point the fruit is inspected to remove any residual cap stems and imperfect fruit. Grading. This may be necessary if a retail pack demands a specific size of fruit. In this case the larger fruit will be screened out for this purpose and the smaller grade for catering packs. Packing. Catering packs are normally 301b (or 13.5kg) and retail packs Fumigation. This should be carried at regular intervals by methyl bromideina fumigatingchamberat thcrateof2.1 kg per 1OOcumofchamber space. This applies to the sweat boxes and to the final packs. BIBLIOGRAPHY W.B. Van Arsdel and A.I.Morgan. jr. Food Dehydration 1973 Californian Golden Bleach Raisins 11 :I 73. 500g. 191