WITH FORCED-AIR1 RAPID COOLING OF FLORIDA CITRUS FRUITS. Most of the existing driers do a fair job of removing the fines, but they also remove the

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1 262 FLORIDA STATE HORTICULTURAL SOCIETY, The fines, if the requirements of (1) and (2) are met, and even if they are not met, will be dry at the end of the first pass. These must be removed quickly from the machine so as not to be burned or ground into dust. Medium sized particles likewise must be removed as soon as they are dry enough. 4. The coarse particles, particularly the large pieces of peel, must be retained in the drying zones long enough to lower their moisture content to about 10%, or close to the average desired product mois ture. 5. The separator must be efficient. Most of the existing driers do a fair job of removing the fines, but they also remove the coarse particles before they are dry. As a result, to secure the desired moisture content in the bag, the fine portions must be over dried in order to give an average bag moisture content of about 8%. These over-dried fines are prone to break up into dust in the drier and in the equipment between the drier and the bag. Summarizing these points, it is necessary to: 1. Introduce hot gas into the drier at a tem perature below 1200 F. 2. Mix this immediately and continuously with a large quantity of feed to reach a tempera ture of approximately 500 F. at the end of the first pass in the drier. 3. Remove the easily dried portion of the feed from the drier as soon as the moisture con tent is low enough. 4. Retain the difficulty dried particles of feed in the drying zones until their moisture content is close to the desired product moisture. 5. Use an efficient separator. I do not know of one drier, either steam or direct fired, which can meet all of these points which are necessary for producing the best quality feed and, in connection with direct fired driers, are necessary in order to avoid smoke and dust nuisances. The principal failing of the steam drier is in connection with No. 3. The fines are, in fact, in the drier longer than the coarse particles. The fire driers fail on all points, on one, two, four and five, by design deficiencies, and on number three because the operator finds it necessary to over-dry the fines in order to compensate for the under dried coarse particles. There is a feed drier recently installed for use on unpressed peel reported to meet its design capacity and also be practically smokeless and dustless. This is not due to the solving of the design problems, but rather to some improve ments in design combined with the much higher moisture content present in unpressed peel, which makes it harder to burn the peel. There are several "flash evaporators" in stalled in the state. These are direct fired units which mix the incoming press liquor with flue gas from a furnace, resulting in evaporation of part of the moisture in the liquid. Such carbon ized particles as are formed from the juice are mostly picked up by the scrubbing action of the apparatus. However, such smoke as is formed will escape with the vapors and appear as a blue or brown trail downwind, starting at the point where the white steam plume from the apparatus has dissipated. The only variable here that the operator has control over is the furnace tem perature. This is generally regulated by the capacity required or by the amount of carbon ized particles which can be tolerated in the molasses. The result is that this apparatus con tributes to the air pollution problem. The author has dust and smoke abatement projects under way at five processing plants. Two of these are combined with heat recovery projects. It is too early to report results at this time. RAPID COOLING OF FLORIDA CITRUS FRUITS WITH FORCED-AIR1 J. Soule, G. E. Yost and A. H. Bennett2 lapproved as Florida Agricultural Experiment Stations Journal Series No Assoc. Hort., Dept. of Fruit Crops, Univ. of Florida, Gainesville; Ag. Engr., USDA, Wenatchee, Wash.; Ag. Engr., USDA, Athens, Ga., respectively. Introduction More than half of the citrus fruits shipped from Florida in recent years has been packaged in half-box or smaller containers (3). Many packing houses have installed machinery for fill-

2 SOULE, YOST, BENNETT: RAPID COOLING CITRUS 263 ing bags. Automation of packing facilities has led to renewed interest in precooling prior to packing. Citrus fruits succumb rapidly to decay when placed in poorly ventilated surroundings, such as exist in polyethylene bags or bagmaster cartons (8, 11, 16, 18), but cooling of packed containers, either by conventional methods of air precooling or refrigeration facilities of truck or rail cars (19, 22) is very slow, too slow for the volume of fruit shipped daily during the sea son from a large citrus packing house. Some packing houses have installed hydrocoolers in their lines. Water is an effective, economical medium of heat transfer that makes it possible to cool fruit more rapidly and less expensively than ordinary air precooling. Studies by Grierson and his co-workers (4, 5, 7, 8, 11, 13, 14, 15) at the Florida Citrus Experiment Station have shown the hydrocooling has a number of unde sirable features, such as the necessity of includ ing a fungicide in the cooling water to hold decay to a tolerable level, a more rapid subsequent decay upon warming of «hydrocooled fruit (over that of fruit held continuously cold), and chilling injury with certain varieties, notably grapefruit. All of this has stimulated new interest in air as a cooling medium. Guillou (12) mentioned that work on forcedair precooling of perishable produce was started in California in By 1958, a dozen commer cial forced-air precooling installations were made in the state. The direct antecedent of the re search discussed herein was a study conducted in Florida by Grierson and Hay ward (9, 10). Markedly improved air cooling of oranges in polyethylene bags in special bagmaster cartons (slotted top and bottom) was obtained when the latter were stacked tightly and a small pressure differential was maintained across the stacks in a slightly modified conventional air cold storage. A joint project between the U. S. Department of Agriculture and Florida Agricultural Experi ment Station was initiated in 1961 at Gaines ville. This research was undertaken to explore as fully as possible the engineering and biological aspects of forced-air precooling. Grierson and Hayward (9) demonstrated that a properly de signed cold air storage could cool packed con tainers in 4 to 6 hours. Emphasis in this investi gation, therefore, was placed on cooling of fruit in bulk on a pilot-plant scale. Pallet boxes, which contain about 1000 lb. fruit when fully loaded, were chosen to permit experimentation with quantities of fruit such as might be precooled by a small commercial packing house. A wide range of operating conditions, some involv ing redesign of the precooler, was purposely included to fully determine the effects of forcedair precooling on oranges, grapefruit, tangerines, and tangelos with respect to physiological break down and decay, along with cooling rates, power requirements, and efficiency of operation. Experiments in the forced-air precooler were carried out over two seasons. In , 144 precooling test runs under a variety of experi mental operating conditions were conducted. In addition, the work consisted of construction of the precooler, breaking-in of equipment, installa tion and calibration of instruments, a survey of possible patterns of air movement in the pre cooling system, measurements of air flow and, finally, major modifications in design of the pre cooler. In , 114 precooling test runs were made to compare rates of cooling with similar test runs of the previous season, random-filled and place-packed fruit in pallet boxes, effect of different fan speeds, and fruit packed in small containers. Because of the December, 1962 freeze, 40 test runs on effect of fan speeds were combined with a study of temperature distribu tion in oranges, grapefruit, and tangelos. Test runs, involving fruit in small containers, had to be deferred until oranges with minimal freeze damage could be obtained late in the season. A detailed account of the investigation will be found in Soule, Yost, and Bennett (20, 21) and Bennett, Soule, and Yost (2). A brief summary of the principal findings is presented herein. Materials and Methods Test fruit. Nine varieties, 'Hamlin/ 'Parson Brown/ 'Pineapple/ and 'Valencia' oranges; 'Duncan/ 'Marsh/ and 'Foster' grapefruit; 'Dancy' tangerines; and 'Orlando' tangelos were tested. Fruit for most of the precooling experi ments was obtained from the Citrus Experiment Station, Lake Alfred, and the Department of Fruit Crops grove on the University of Florida campus. Fruit was tree-run, washed, and "waxed." None was degreened. Fruit from the Citrus Experiment Station also received fungicidal treatment. Two lots of 'Valencia' oranges were donated from Mims Citrus Groers Association and Nevins Fruit Company for test runs of fruit in small containers. Fruit was obtained at intervals of 3 to 4 weeks during the season and stored at 40 F. until tested.

3 264 FLORIDA STATE HORTICULTURAL SOCIETY, 1965 Containers. Most of the investigation was carried out with two types of pallet boxes, the standard commercial slatted wooden box (6) and the expanded metal mesh box. Dimensions were 42 x 42 x 26 in., and 42 x 42 x 30 in., re spectively. Capacity with 26 in. depth of fruit was approximately 1000 lb. Per cent opening in the wooden box bottom was 6.5, and in the ex panded metal, Prior to the season, a simulated pallet box, with solid sides and removable bottom, was built into the precooler. Small containers, used for 25 test runs, included 4/5 bu. wirebound boxes, 4/5 bu. fiberboard cartons, loose 8-lb. polyethylene bags, and 8-lb. polyethylene bags in bagmaster cartons. Precooler. The pilot-plant, forced-air pre cooler was designed for circulation of cold air, at' various flow rates, around fruits to provide for forced-convective heat transfer between air and surfaces of individual fruits. The initial capacity was 2 pallet boxes, i.e lb.; this was later reduced to 1000 lb. Insulation was expanded polystyrene, 3-in. thick, with inner and outer polyethylene vapor seals and covered with 0.5 in. plywood. Numerous minor and sev eral major modifications were made in the pre cooler as work progressed. The final version, used in , is shown in Fig. 1. Air was circulated with a 11,500 cfm. backward-curve fan equipped with variable speed drive and inter changeable pulleys. A damper provided further regulation of air flow. Warm air leaving fruit was chilled^,by passing it over 3 sets of finned evaporator coils. Each set of coils were cooled by a 3-hp. compressor and 1.5-ton condensing unit capable of maintaining a coil temperature as low as 0 F. A 2000-watt resistance heater was located in the fan outlet to assist in rewarming fruit. A small blower with an auto matic damper beneath the evaporator coils was installed to circulate air during "temperature pull-down." Instrumentation. Power consumption of the fan and compressors was measured with indus trial watt-hour meters. Static pressure drop across the fan was determined with a wallmounted vertical manometer. Readings of air flow in the system were made with a portable anemometer. Air and fruit temperatures were sensed with copper-constantan thermocouples DAMPER PRODUCT CHAMBER AIR STRAIGHTENERj VANES 11,500 c.f.m. FAN EVAPORATING COILS PLENUM CHAMBER RECIRCULATING FAN LOUVER FORCED-AIR PRECOOLING CHAMBER Figure 1.

4 SOULE, YOST, BENNETT: RAPID COOLING CITRUS 265 connected to recording potentiometers. Thermo couple junctions for air were 24 a.w.g.; those for fruit were 30 a.w.g. with 24 a.w.g. leads. Experimental procedures. Since there was very little background of forced-air precooling of citrus fruits in Florida (17), the first task was to establish operating parameters which would enable fruit to be cooled quickly without excessive injury. A preliminary survey was made which included 6 air patterns (3 with 1000 lb. and 3 with 2000 lb. of fruit), several air temperatures from 35 F. down to 5 F., and fan speeds from 1000 to 1500 rpm. From this a procedure was established for precooling test runs that, with some modifications, became stan dard throughout the investigation. Experiments were grouped into series in which a given variety and pallet box was precooled using 3 load sizes (250, 500, and 1000 lb.) and 4 rates of air flow (maximum, %, %, and % maximum). Initial fruit temperature was 70 F., except where this was a variable. Initial air temperature was 15 F. Fan speeds used were 1400 rpm. (approx imately 12,000 cfm. maximum air flow), 1030 rpm., and 670 rpm. All test runs conducted in and about 45 in were conducted with 1400 rpm fan speed. Each test run con sisted of a "temperature pull-down" period, in which portions of the system outside of the load were cooled to 15 F. as measured at the fan in let, and a precooling period. In the first 9 series of test runs, precooling was continued until the temperature at the center of orange and tanger ine fruits reached 40 F. and of grapefruit, 50 F. Subsequent test runs were made for a definite time interval, usually 1.50 hr. Fruit was counted and weighed periodically to deter mine loss in weight, presumably moisture. Un sized fruit was used in test runs, but sized fruit was used in The same fruit was precooled repeatedly with the addition of new fruit between trials only to bring a load up to desired weight or to replace decayed fruit. Measurements of power consumption and static pressure were taken at the beginning and end of each test run. Air flow tests were conducted separately from precooling test runs for each combination of fruit variety, pallet box, load size, fan speed, and 10 damper settings from fully closed to fully open. Data were converted to standard temperature and barometric pressure. Results and Discussions Experimental variables investigated in the forced-air precooling study were 9 varieties of oranges, grapefruit, tangerines, and tangelos, 9 air patterns, 3 load sizes, 3 fans peeds, 5 initial fruit temperatures, 2 types of pallet box, 2 methods of filling pallet boxes, and 4 types of small container. Preliminary Survey. The preliminary sur vey of 6 patterns of air movement through the precooling system brought out 3 important points which were corroborated repeatedly in later test runs. First, all of the air should go through the load if cooling is to be effective. The process of forced-air cooling of fruit has 2 components, transfer of heat from the interior of a fruit to the surface by means of conduction and transfer of heat away from the surface by means of convection. The latter must be ac complished in order for the former to be effec tive; thus air by-passing the load is wasted. Second, a study of air movement through the load from side to side, from one side end and out the top, or from two sides and out the top showed that the most efficient system is one in which air moves vertically, preferably upward. Cold air absorbs heat from warm fruit in pass ing through the load and tends to rise; there fore, more efficient use of refrigeration is obtained when air is introduced into the bottom of the load, the cold side, first. Third, cooling of fruit was accelerated as initial air tempera ture was reduced from 35 F. to 5 F. Fruit exhibited no sign of immediate of subsequent physiological breakdown or increased. decay, regardless of the initial air temperature, pro vided surface temperature of the fruit did not drop below 25 F. An initial air temperature of about 15 F. was chosen for precooling test runs, since this gave rapid cooling, did not result in freezing up of the evaporator coils, and required a "temperature pull-down" period of only about 0.50 hr. Rate of Cooling. Typical cooling curyes for 'Valencia' oranges and 'Duncan' grapefruit are shown in Figure 2. Fruit temperature at the center (tc always dropped more "slowly than surface temperature (ts). There was a lag of 0.25 to 0.50 hr., most pronounced with grape fruit, at the beginning of precooling before center temperature dropped appreciably below the initial value. Subsequent to this lag period, there was a series of nearly uniform tempera-

5 266 FLORIDA STATE HORTICULTURAL SOCIETY, 1965 ture gradients from center (tc) to surface (t8) of fruit, from surface of fruit (tg) to adjacent air, (21^) and from air around fruit (1^,) to air next to refrigeration units (ta). Refriger ation capacity was not adequate to maintain a uniform air temperature; therefore, rate of cooling was dependent upon the rate of heat removal from the system as a whole. Four principal variables were found to affect cooling rate. These were variety, load size, fan speed, and initial fruit temperature. Oranges, tan gerines, and tangelos were precooled from initial mass-average temperatures (21) of 70 to 90 F. down to 35 to 50 F. in an hour or less. The most rapid cooling rate was obtained with about 3500 cmf. air flow. Grapefruit cooled a little more slowly than oranges. The cooling rate was directly correlated with fruit size as modified by shape, rind thickness, presence of a hollow center, and other fruit factors. Tangerines and tangelos cooled a little more rapidly under com parable conditions than oranges and grapefruit, but not as rapidly as their small size would have indicated. On the other hand, grapefruit did not cool as slowly relative to oranges as their comparative size would have led one to expect. A possible explanation of these results may lie in the proportion of rind to pulp in volved, since Bennett, Chace and Cubbedge (1) showed that rind and juice vesicles have marked different thermal conductivities. The smallest (250 lb.) of the 3 load sizes used in the precooling test runs cooled the fast est, and the largest (1000 lb.) the slowest. The situation was just the reverse, however, when the total amount of heat removed was consid ered. Nearly 3 times as much heat was removed from a 1000 lb. as compared to 250 lb. load for a given quantity of refrigeration capacity (19). Efficiency of precooler operation increased and cost per pound of fruit cooled decreased rapidly as load size was increased. Effects of fan speed upon rate of cooling were twofold, with respect to rate of air move ment and heat produced by the fan and its motor. At the maximum fan speed of 1400 rpm., air flow through a load of fruit ranged from about 3000 to 12,500 cfm. Approximately 40 IOO VALENCIA ORANGES.50 LOO L50 TIME (hrs.) DUNCAN GRAPEFRUIT i **** 50 IDO 150 TIME (hrs.) Figure 2. Time- tempera ture curves for 500 lb. loads of 'Valencia1 oranges (test run 75) and 'Duncan' grapefruit (test run 50), standard wooden pallet box. (tc center of fruit, ts " surface of fruit, t > average of air in box, ta air next to fan inlet)

6 SOULE, YOST, BENNETT: RAPID COOLING CITRUS 267 pet. of the precooler's refrigeration capacity was required to remove heat introduced into the system by the fan. At 670 rpm., maximum air flow through a load varied from about 2700 to 5600 cfm. However, less than 5 pet. of the refrigeration capacity was required to offset fan heat. Cooling of fruit at 670 rmp. fan speed was in fact so rapid that the precooling period had to be reduced to 1.00 hr. from the usual 1.50 lest fruit be frozen. The influence of initial fruit temperature upon rate of cooling is shown graphically in Fig. 3. Progressively more heat was removed from 'Valencia' oranges as initial temperatures was raised from 70 F. to 95 F. Oranges packed in 4/5 bu. wirebound boxes, ventilated 4/5 bu. cartons, or loose 8-lb. poly ethylene bags precooled about half as fast as bulk fruit. Bagged fruit in non-ventilated bagmaster cartons precooled very slowly (19). Efficiency and costs of electricity. Precool ing system efficiency, i.e. the proportion of the refrigeration capacity devoted to removal of heat from fruit, ranged from 22.4 to 58.2 pet. among test runs of oranges in pallet boxes and from 1.0 to 18.6 pet. for oranges packed in small containers. Total cost of electricity (at ioo,95 :75 SURFACE CENTER FINAL FRUIT TEMPERATURE ( F.) Figure 3. Fruit temperatures of 500 lb. loads of 'Valencia' oranges precooled for 1.50 hr. in standard wooden pallet box. per kwh) was from 19.4 to 42.0 cents for 1.00 hr. of precooling. Cost per pound varied from to mill. Biological effects of precooling. Loss in weight, presumably moisture, from fruit during precooling ranged from about 0.1 to 0.2 pet. per test run. Humidity control, which would have been difficult with the low air temperatures used, was not attempted. Loss of moisture to the point of causing visible shrinkage was never a problem even when the same fruit was pre cooled from 12 to 24 times. A primary concern at the outset of the in vestigation was whether fruit would show phy siological breakdown and increased decay when it was subjected to the low temperatures neces sary for rapid precooling. Even among grape fruit, rind breakdown as a result of precooling was virtually nonexistent. None was found with other varieties, except for one series of test runs with tangelos at 670 rpm. fan speed. Here, fruit in the bottom third of the load was frozen when surface temperature was dropped to about 19 F. If care was taken to keep surface tem perature to 25 F. or above, there was no injury with these or other fruits. Decay in the course of over 230 precooling test runs with loads from 250 to 1000 lb. amounted to a few hundred fruit, or far less than expectation considering the abuse to which this fruit was subjected. LITERATURE CITED 1. Bennett, A. H., W. G. Chace, Jr., and R. H. Cubbedge Thermal conductivity of Valencia orange and Marsh grapefruit rind and juice vesicles. ASHRAE Trans actions (In press). 2, J. Soule, and G. E. Yost Tem perature response of Florida citrus to forced-air precooling. Summer meeting ASHRAE, Portland, Oregon, July 5-7, Florida Department of Agriculture Annual Report Division of Fruit and Vegetable Inspection Fla. Dept. Agr. 76p. 4. Grierson, W Preliminary studies on cooling Florida oranges prior to packing. Proc. Fla. State Hort. Soc. 70: Dowicooling. Fla. Citrus Exp. Sta. Mimeo Rept. No (comp.) Handling Florida oranges in pallet boxes. U. S. Dept. Agr. Marketing Res. Rept p. 7 - and F. W. Hayward Hydrocooling studies with Florida citrus. Proc. Fla. State Hort. Soc. 71: and Precooling, packaging, and fungicides as factors affecting appearance and keeping quality of oranges in simulated transit experi ments. Proc. Amer. Soc. Hort. Sci. 76: and Precooling of Florida citrus fruits. Fla. Agr. Exp. Sta. Ann. Rept. 1960: and Precooling of citrus fruits. Fla. Agri. Exp. Sta. Ann. Rept. 1961: ,, and M. F. Oberbacher Simulated packing, shipping, and marketing experi ments with Valencia oranges. Proc. Fla. State Hort. Soc. 72:

7 268 FLORIDA STATE HORTICULTURAL SOCIETY, Guillou, R Coolers for fruits and vegetables. Cal. Agr. Exp. Sta. Bui p. 13. Hayward, F. W Water damage in the hydrocooling of citrus fruits. Proc. Fla. State Hort. Soc. 75: and W. G. Long Precooling of citrus fruits. Fla. Agr. Exp. Sta. Ann. Rept and M. F. Oberbacher, Effects of continuous refrigeration on the keeping qualities of oranges. Proc. Fla. State Hort. Soc. 74: , _.., and W. Grierson Perforations in polyethylene bags as related to decay of oranges. Proc. Fla. State Hort. Soc. 74: Leggett, J. T. and G. E. Sutton Precooling of citrus fruits. Fla. Eng. Indus. Exp. Sta. Bui p. 18. McCornack, A. A. and E. F. Hopkins Decay and rind breakdown of oranges in fiberboard cartons and wirebound boxes. Proc. Fla. State Hort. Soc. 75: Rose, D. H., H. T. Cook, and W. H. Redit Harvesting, handling, and transportation of citrus fruits. U. S. Dept. Agr. Bibliog. Bui p. 20. Soule, J., G. E. Yost, and A. H. Bennett Certain heat characteristics of oranges, grapefruit, and tangelos during forced-air precooling Ann. meeting Amer. Soc. Agr. Eng. Paper No ,, and Forced-air precooling of Florida citrus fruits. U. S. Dept. Agr. Tech. Bui. (In preparation). 22. Winston, J. R Harvesting and handling citrus fruits in the Gulf States. U. S. Dept. Agr. Farmer's Bui p. (revised). THE SYSTEMATIC ANALYSIS OF VOLATILE FLAVOR COMPONENTS IN R. W. Wolford, J. A. Attaway, and L. J. Barabas2 Abstract Solvent extracts of high quality orange essences were analyzed systematically using gas chromatography, thin layer chromatography, infrared spectroscopy, and mass spectrometry. By employing several combinations of these techniques the identities of 41 compounds from five chemical classifications were confirmed. These were aldehydes and ketones, alcohols, acids, terpene hydrocarbons, and esters. Four additional components were assigned tentative identifications. Preliminary results of analyses, using dual channel flame ionization and electron capture detection systems in gas chromatography, are presented to show an additional tool available for the analysis of complex mixtures of flavor components. Introduction Investigations concerning the volatile flavor of orange juices have required a workable knowledge of the types of chemical compounds contributing to the flavor. Although the ulti mate criteria of acceptability for processed citrus products lie, in flavor appeal as determined by ddor and.jtaste, the objective development of such knowledge using instrumental and chemical methods has been necessary. This is true Florida Agricultural Experiment Stations Journal Series No lcooperative research by the Florida Citrus Commission and Florida Citrus Experiment Station. 2Florida Citrus Commission, Lake Alfred, Florida. ORANGE JUICES1 whether it be for controlling their retention in processed products, such as, frozen concentrated orange juice or for recovery of the flavor com ponents as usable material for subsequent addi tion to the product. Through the application of gas chromatog raphy to analysis of volatile flavor components of Florida citrus juices (10) was provided a quick and efficient method for separating these flavor producing compounds. Likewise, it helped to overcome one of the principal obstacles to a successful completion of such investigations, namely, the separation and detection of materials present in only minute quantities in juices and recovered juice essences. Other publications (11, 12) have since described the analysis of flavor components in orange essences. SubtxactWe pro cedures (11) have revealed many trace com ponents and indicated that incomplete resolution of the complex mixture frequently caused two or more suspected compounds to have the same relative retention time. These factors posed some difficult problems in identification, some of which were resolved by derivative formation and characterization, adsorption, paper partition and thin layer chromatography. The identification of carbonyls, saturated aliphatic alcohols, ter pene alcohols, and organic acids (1, 2, 3) are good examples of the use of these supplementary techniques. Also, the application of thin layer chromatography to the analysis of esters, terpene hydrocarbons, aldehydes, ketones, and alcohols (4, 6, 7) provided confirmation for previously identified components. The use of re-chromatography by programmed temperature gas chromatography (PTGC) and flame ionization detection (PTGG-FI) on fractions collected from the thermal conductivity detection systems, to-