7 Dehydration 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 followingin order of tonnage produced Other countries with a substantial export trade in dried fruits are Greece(producing 90 percent of the worlds currant supply), Iran, Turkey, Portugal, Iraq, Algeria, Australia, Argentina, Egypt and South Africa. Of the above, the Middle East countries are particularly importantin the drying of grand 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 pes ofraisin. With cut fruits, particularly apricots, pears and peaches, it has ong been considered that using solarenergy 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 70s 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
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, which suffer from splitting of skins with a 100Cblanch, and this was eliminated by a temperature reduction to 92"C. Sulphating 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 simila manner to that used in tunnel drying. The trolleys are pushed into the lphuring shed, which is fitted with a sulphur burner at the bottom end with adequate venting to atmosphere, either by natural draught or by fan, hrough 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 SO2 in the sulphur 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 golden-bleach raisins which contain levels of SO, up to 2000p 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 Apricotson the basis ofthe authors trials, it could equally be used for Pears and Peaches, Apple Rings and natural Raisins Apples(Rings and Flakes) (1) Flow Sheet Feed to Li
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
hing ding Peeling-Coring Sulphating g sulphite on g (2)Varieties USA: Baldwin, Delicious, Jonathan, Permian, Winesap UK: Bramley Seedling( Cooking variety) Left: A Fruit Washerproduced by the Bead Engineering Comp
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 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 symmetricalshape, which makes mechanical peeling easierand 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 downin Preparation and low acidity. However, they are grown more widely in America and Europe than almost any other dessert apple, and may be sed 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 Diameter Weight per fruit No per kg No per tonne in mm 14.286 14,286 11.765 11,765 115 8.696 8696 155 210 4.762 4,762 Subject to slight variation as between varieties. Peeling and Coring There are three options: (a) Hand peeling (b)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, Flash steam peeling can be carried out in a short immersion steam peeler operating at 17atm, and normally 15 seconds exposure time is
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 manufacturers rated throughput is more realistic. More manual trimming is often required after le 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% efficien @75% efficien 8 hours 2016 552 3312 4464 From the above factory figures, based on an actual days 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 a 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 lift simultaneous movement and removes the stem, calyx and seed cells in one a peration. The peeled and cored apple is then mechanically ejected from the spindle downa chute and on to a 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 ither a 1.5 percent salt solution or sulphite solution to prevent browning and oxidisation. This is most conveniently done in a flume which delivers
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