1998 CORNELL FRUIT HANDLING AND STORAGE NEWSLETTER

Temperature management of apple fruit for maintenance of quality

We have been carrying out a project funded by the Statewide Program Committee Research/Extension Grants program to investigate temperature management of apple fruit for maintenance of quality for local and export markets. Problems in meeting firmness standards for fruit, particularly those exported to Europe, has been a major factor in deciding to put research and extension effort in to this area. A key objective of this study is to measure the effects of current temperature management strategies on apple fruit quality. Our initial approaches have involved obtaining base information on temperatures during different parts of the handling chain.

1. Effects of current packing operations on fruit temperatures

Skin and core temperatures of fruit from various positions on the packing line have been measured in nine packing houses (Table 1). Fruit that were tested included McIntosh, Empire, Delicious and Idared, and packing lines were operating with and without waxing. The data show that the warming of fruit can be rapid, even while in bins prior to entering the water dumper. The effects of the water dump process varied according to whether water was heated or not. However, by the post-dryer step, skin temperatures averaged 67^oF (individual operations ranged from 59 to 77^oF), while core temperatures averaged 43^oF (range from 39 to 50^oF). These temperatures were reached even when fruit were not actually being waxed. While on the sorting tables, core temperatures of fruit continued to increase. Technically, only heat moves. Surfaces warm first due to water and dryer temperatures being greater than apple temperatures. Later, as temperatures equilibrate, the core warms as the surface cools, and both become equal. In some cases, especially on rotary tables where fruit may revolve for some time before being packed, very high fruit temperatures were obtained. Temperatures of packed apples commonly exceeded 60^oF.

Packing is obviously necessary for the industry and warming of the fruit during this process is unavoidable. These data do, however, highlight a couple of important steps that can be taken to minimize warming and the time that fruit sit in warm conditions. The most important of these starts in the storage room prior to moving bins of fruit to the water dump. Temperatures in these rooms should be maintained at 32^oF for all varieties. Secondly, only the required number of bins to maintain the packing operation should be brought from the storage rooms. Operations that remove a morning's run at one time, for example, will cause undesirable warming of fruit to occur. Now that we have established the warming cycles that occur during packing operations the question that arises is, "What happens to temperatures of packed fruit?"

2. Cooling rates of fruit in packed cartons

Cardboard is a great insulator, so a warm product inside a sealed carton on a pallet will take a long time to cool. So far, our data for temperature changes over time in standard cartons are limited to one test in which fruit temperatures of 100 count McIntosh apples were measured over 10 days (Table 2). We put temperature probes (Figure 2) in single fruit in the center of cell packed cartons. These electronic probes can record temperatures over time and the information is downloaded by computer (Figure 3).

The cartons were positioned in a middle carton of the bottom, top and middle layers.

We measured two factors.

1. The time that it took for fruit to cool from the initial packing temperature. Sometimes, fruit actually warmed up during this period because heat was produced faster by fruit respiration than it was removed by the surrounding cold air. Interior fruit temperatures always exceeded exterior exposed fruit temperatures during cool-down.

2. The half cooling time is a standard index for expressing cooling effectiveness. This measures the time that is required to remove 50% of the heat from the apple. For example, if fruit temperatures are at 72^oF in a storage room at 32^oF, the temperature difference between the fruit and final desired temperature is 40^oF. A half cooling time of 8 hours means that it will take that time to reduce fruit temperatures by 20^oF to 52^oF, and a further 8 hours to reduce fruit temperatures by 10^oF to 42^oF. Fruit are generally considered "cooled" after three half cooling times (75% of heat removed). In the example, three half cooling times would equal 24 hours and the fruit temperature is 37^oF. Fruit will continue to cool to 32^oF if left in the 32^oF room.

In our trial, we found that the fruit in a center carton in the bottom layer of the pallet stack took 13 hours before any cooling occurred, and the half cooling time was 69 hours (Table 2). In other words, fruit in this carton took almost 9 days to "cool" after packing! Fruit in other positions cooled faster, but clearly still slower than desirable. These temperatures probably reflect commonly found cooling rates, although cooling in tray packed cartons is probably faster than that observed in the present study for cell packed cartons.

3. Methods by which cooling rates of fruit can be increased

We are investigating ways to improve cooling rates of apple fruit in packed cartons. Cartons with vents designed to allow air from the cold room to flow over the fruit are commonly used for apples from some growing regions. These cartons have been a standard for produce like grapes and tomatoes for many years. Figure 4, for example, shows New Zealand apple cartons with venting designed to maximize cooling rates. However, such cartons have not been used in New York. We compared the effectiveness of vented and standard cartons with handholds only under both passive and forced-air systems. Passive cooling was defined as cooling palletized cartons only in a traditional cold storage, while forced-air cooling utilizes a fan to actively pull cold air through and around cartons of fruit. Two tests for each carton/cooling combination were carried out using the 60 x 40 export carton for Empire. We inserted temperature probes into an apple placed in the center of the top tray in the 10th layer from the bottom (14 layer pallet) in positions indicated in Figure 5.

Fruit half cooling times were affected by location, but the effects of venting and cooling method were the most dramatic (Table 3). Note that in non-vented cartons, long delays occurred before fruit cooling was begun. In addition, two features of fruit temperature responses are particularly interesting. First, forced air cooling was about ten times faster than passive cooling, regardless of the presence of vents. Even with no vents, cooling of fruit would be complete within 24 hours (half cooling time x 3). Second, the presence of vents resulted in much faster cooling (approximately 2.5x faster) regardless of cooling method, although half cooling times still averaged 29 hours in passively cooled cartons.

4. Summary

This project is ongoing and further research is required before firm recommendations about carton design can be made to the industry. Although we have found in separate experiments that CA-stored fruit packed in April were 0.5 lb firmer when kept at 32^oF than 41^oF for only two weeks, the relationship between carton temperatures and fruit quality has not been established. This is a priority for future research, especially for export fruit where problems with firmness maintenance continue to plague the industry. An important outcome of this study may be that fruit with lower flesh firmness can be exported and still meet quality standards overseas. Carton venting, however, also brings an additional set of issues including faster warming of packed fruit if the cold chain is interrupted. Also, successful development of better cartons will require collaboration with manufacturers to ensure that carton strength is not compromised.

Nevertheless, our studies to date highlight the need to consider temperature management at all stages of the operation from harvest to market. The industry is actively concerned with cooling of fruit before storage, but this concern must also address the issues of temperature control during packing and transport.

Controlling postharvest decays on apples

Recommendations for controlling postharvest decays on apples remain largely unchanged from previous years and are summarized at the end of this article. Thiabendazole (TBZ, sold as Mertect 340F) and captan continue to be the only chemical fungicides with postharvest labels for apples. Several biocontrol fungicides are registered, but they are either unavailable in New York or ineffective under commercial conditions. Effectiveness of TBZ has been decreasing in recent years because of fungicide-resistance problems. Captan provides good control of postharvest decays when used at the full label rate of 2.5 lb per 100 gallons of drench solution, but use of captan is limited by zero-residue tolerances for captan in some export and US processing markets. In the absence of fully-effective postharvest fungicides, sanitation measures become increasingly important for controlling losses to storage decays.

Fungicide-resistance problems with apple postharvest pathogens have gradually increased in severity over the past 25 years. Many strains of Penicillium and Botrytis developed resistance to TBZ and related benzimidazole fungicides (Benlate, Topsin M) soon after these products were introduced in the 1970's. However, the benzimidazole fungicides continued to provide acceptable control of postharvest decays for at least 10 years after resistant strains of the pathogens were present in storages. Research in the mid-1980's showed that most of the benzimidazole-resistant strains of Penicillium expansum and Botrytis cinerea were unusually sensitive to diphenylamine (DPA), an anti-oxidant used to control storage scald on apples. In commercial practice, TBZ and DPA are usually applied together, and that combination provided adequate control of both benzimidazole-sensitive and benzimidazole-resistant pathogens. Effectiveness of the benzimidazole-DPA combination decreased, however, as strains of Penicillium expansum with resistance to both chemicals gradually emerged in the 1990's. These doubly-resistant strains have caused up to 15% decay in some lots of Empire fruit held in controlled atmosphere (CA) storage for 9-10 months after harvest.

Several biocontrol fungicides have federal registrations for postharvest use on apples. Biocontrol fungicides are formulations of bacteria or yeasts- living organisms that actually grow on the fruit after they are applied. Biocontrols do not act by killing pathogen spores or by inhibiting spore germination. Instead, they arrest decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms presumably utilize all of the available nutrients in the wounds, leaving nothing to support initial growth of the decay fungi. The decay fungi utilize the apple juice and damaged cells in wounds as a source of nutrients for initial growth of spores. When this "start-up fuel" is consumed by the biocontrol fungi, the pathogens are left without the nutrients needed to initiate growth.

A series of experiments was conducted with the biocontrol product, Decco I-182, during the 1997 harvest season to determine if it could be used alone or in combination with TBZ to control mixed populations of TBZ-sensitive and TBZ-resistant P. expansum. Decco I-182 is a formulation of the yeast Candida oleophila that was formerly marketed as 'Aspire'. Results from the 1997 trials showed that although Decco I-182 was sometimes as effective as the standard DPA/TBZ combination, it was never superior and its effectiveness seemed to fade as the duration of storage increased. Furthermore, there was no additive effect or benefit from combining Decco I-182 with the standard DPA/TBZ treatment. With continued research, more effective ways of applying and using Decco I-182 might be devised. In the meantime, however, there seems to be little reason for including this expensive product in postharvest treatments of apples.

Research we conducted over the past 10 years has repeatedly shown that the predominant postharvest pathogen in apples receiving postharvest treatments is Penicillium expansum. In apples that are moved to storage without treatment, decays caused by Botrytis cinerea often predominate. (Apples with Botrytis decay come out of CA storage as firm, tan, completely-decayed fruit that look very much like baked apples.) The biology and epidemiology of Botrytis decays in apples has not been adequately researched under east-coast conditions. However, it seems likely that Botrytis decays are uncommon in fruit receiving postharvest treatments because relatively few strains of Botrytis have developed resistance to both DPA and TBZ whereas such resistance is common in Penicillium.

Empire apples from western NY may require postharvest treatment to control the Botrytis decays that predominate when Empire fruit are stored without any postharvest treatment. We do not know why Botrytis decays are more common in Empire apples from Western NY than in those from the Hudson Valley. However, the prevalence of Botrytis in western NY may relate to growing conditions in the field. In some other crops (grapes, kiwi), researchers have shown that Botrytis infections that occur early in the season remain dormant until fruit begin to ripen. It is quite possible that latent Botrytis infections on apples are favored by the cooler summers (and perhaps cooler and damper conditions during bloom and petal fall) that generally prevail in western NY as compared to the Hudson Valley. If early-season conditions contribute to latent infections of Botrytis on apples, and if these latent infections are a primary cause of postharvest Botrytis decays under NY conditions, then 1998 could be a bad year for Botrytis decays in stored apples because the extended wet periods that prevailed during and immediately after bloom would have favored higher-than-usual levels of infection.

Following are suggestions for controlling postharvest decays of apples for the 1998 harvest season:

1. Apply postharvest fungicide treatments only to when needed. For example, most New York growers have found the Golden Delicious are best stored without any postharvest treatment. Empire produced in the Hudson Valley are frequently stored without any postharvest treatment, but Empire fruit from western NY may require treatment to prevent Botrytis. Fruit held for less than two months in regular cold storage seldom require any postharvest treatment. If DPA must be applied to control storage scald, then TBZ or TBZ plus captan should be applied to control pathogens that will accumulate in the drench solution.

2. Always use DPA and TBZ together because that combination provides better control of both TBZ-sensitive and TBZ-resistant isolates than either product used alone. Follow label recommendations for rates, replenishing solutions, and maximum quantities of fruit that can be treated before the drencher solution must be replaced.

3. Captan used at the full label rate will help to control isolates of P. expansum that are resistant to DPA and TBZ. However, captan-treated fruit may be unacceptable in some markets. Furthermore, captan is again under close regulatory scrutiny because of the Food Quality Protection Act. The captan label might be revised in the near future. Using captan might reduce losses to postharvest decays but could significantly limit marketability of treated fruit.

4. Only use application equipment that has an effective agitation system in the holding tank. Otherwise, the fungicide(s) in the drench solution will settle out of solution on the bottom of the tank.

5. Use the cleanest bins available for fruit that is most at-risk for decay. Thus, where possible, use new bins or sanitized bins for Empire fruit that will be held in long-term storage and be especially careful of drench-water sanitation when these fruit are being treated.

6. Rapid cooling can significantly reduce the incidence of decay that develops in storage. If CA rooms are being filled rapidly, fruit should be pre-cooled in separate rooms before it is loaded in the CA room so as to reduce the total cooling time.

DPA effects on McIntosh and Empire

Last year we reported that McIntosh apples were firmer when treated with a prestorage drench with diphenylamine (DPA), regardless of the presence of calcium salts. This result supported earlier results obtained with Empire apples in 1995. There are two reasons for being interested in these responses. First, the apparent benefit obtained on firmness (and reduction of carbon dioxide injury) of these varieties may sometimes be critical in meeting market requirements. Second, and perhaps as important, is the observation that current handling and storage protocols have developed during a time that DPA application has become standard for the industry. If the chemical is lost to the industry, there may be implications for storage operations that we are not expecting. An excellent example of this possibility, were the increased fruit losses in Empire apples a few years ago because of external carbon dioxide injury. High losses occurred when many operators stopped using DPA, and ironically, the worst problems occurred in those operations with optimal storage conditions such as rapid CA. Historically, carbon dioxide injury used to be a standard problem for McIntosh, but incidence of the disorder now seems low. One reason may be the widespread use of DPA.

During the 1997 season we harvested fruit from 4 orchards in the major apple growing regions during the commercial harvest season. McIntosh apples were harvested from the Champlain, Hudson Valley and Western New York, and Empire only from Hudson Valley and Western New York. On the day of harvest, fruit were dipped in water, DPA, calcium chloride, Mertec 340-F, or a combined cocktail of all chemicals.
McIntosh apples were stored in 2% carbon dioxide and 2% oxygen, or 5% carbon dioxide (in 2% oxygen) after one month at the lower concentration as commercially recommended. Empire apples were stored in 2% carbon dioxide and 2% oxygen. Both varieties were stored for seven months and quality factors measured after one and seven days at 68 ^oF.

For McIntosh, firmness of DPA-treated fruit was always higher than water- or TBZ-treated fruit, but not always higher than calcium-treated fruit (Table x). However, the cocktail of all chemicals resulted in consistently firmer fruit in all growing regions. For Empire, DPA-treated fruit, alone or in combination, were always firmer than any other treatment (Table 1).

External carbon dioxide injury occurred only in Hudson Valley-grown McIntosh, being as high as 13% in fruit from one of the test orchards. Injury was absent in both DPA treatment. Senescent breakdown was found in both varieties and all regions, but was not affected by treatment. Superficial scald was found only in two orchards in the Champlain region, averaging 10%, but was completely controlled by DPA.

The bottom line is that there are clear advantages to use of DPA, over and above, control of scald. However, it is labeled only as a scald-controlling chemical. If you are not currently using DPA we recommend that you continue to avoid its use. However, if you are using it, you need to know that it may be resulting in effects over and above prevention of scald development during storage. If the industry loses DPA for scald control, recognition of the impact of these other effects may become important especially as they relate to firmness and susceptibility of fruit to carbon dioxide injury.

Table 3: Effect of postharvest drench of water, DPA, CaCl2 and/or TBZ1 on firmness of 'McIntosh' and 'Empire' apples.2, 3
Cultivar	Treatment	Firmness (lb)
		Champlain	Hudson Valley	Western NY	Average
McIntosh
	Water	13.4	13.5	13.8	13.6 c
	DPA	13.5	13.8	14.2	13.8 ab
	CaCl2	13.3	13.7	14.0	13.7 bc
	TBZ	13.3	13.4	13.9	13.5 c
	DPA,CaCl2,TBZ	13.8	13.8	14.4	14.0 a
Empire
	Water	-	15.5	15.1	15.3 b
	DPA	-	15.8	15.5	15.7 a
	CaCl2	-	15.4	15.1	15.2 b
	TBZ	-	15.4	15.1	15.3 b
	DPA,CaCl2,TBZ	-	16.0	15.6	15.8 a
1 1000 ppm DPA; 25 lb/100gal CaCl2; 16 fl oz/100gal Mertec 340-F
2 For McIntosh, fruit were stored at 2% CO2 throughout or in 2% CO2 for one month then 5% CO2 (in 2% O2). Fruit were measured after 7 months and firmness readings are the average of 1 and 7 days shelf life at 68oF
3 Four orchards harvested in each region.

Rapid CA establishment using nitrogen

Air separation equipment and cryogenic Nitrogen have been in common use in the northeast for over ten years However, we still receive questions on the use of liquid nitrogen and the operation of air separators, so a review article on the subject seems to be in order. The two topics of the day are safe and effective application of liquid nitrogen, and operation of the air separator for rapid pulldown of oxygen.

Liquid Nitrogen

In 1986 we summarized our recommendations for liquid nitrogen use in rapid CA. Purging or "flushing" CA rooms is a very quick way of reducing the Oxygen level and it also eliminates the problems of CO₂ accumulation and hydrocarbon contamination experienced with catalytic burners. There are, however, some cautions to be observed when using liquid nitrogen.

The boiling point of liquid nitrogen is -320°F and it must be handled carefully to prevent injury to people and apples. We originally recommended introducing the liquid nitrogen directly into the CA room. This was because
external nitrogen vaporizers were not commonly available and without the vaporizer, the flow of gas from the Dewar was slow. With direct injection of liquid, a Dewar containing 45 gallons of liquid (3600 cubic feet of nitrogen gas) could be safely emptied in 20 to 30 minutes, but this procedure always left some freeze-damaged apples in the room. The loss of fruit and concern about ethylene produced by the spoiling apples caused most operators to use a vaporizer and convert the cold liquid to a gas before piping it to the CA room. Bulk truckloads of nitrogen are now commonly offloaded as vapor and nitrogen from Dewars may need to be fed through a vaporizer in order to achieve an acceptable purge rate for rapid CA.

Operators who use nitrogen routinely generally know how much nitrogen they need for each CA room. Those contemplating using nitrogen for the first time may wish to estimate the volume needed so that they can determine the cost or reserve a supply. Estimated liquid and gaseous nitrogen use per 1,000 bushels of storage is shown in Table 1

Liquid nitrogen is sold by the liter. One liter of liquid expands to 20 cubic feet of gas when it vaporizes. It is imperative that you monitor the room pressure when the nitrogen is being applied. Gaseous nitrogen is safer from a room pressure standpoint than direct injection of liquid, but it is still possible to over pressurize the room and destroy the gas seal if the nitrogen flow into the CA room exceeds the capacity of the port hole or exhaust vent. Room pressure should never exceed one inch of water column pressure.

Before establishing the atmosphere, lock or seal all gas tight windows and doors and placard all access points with "Danger-Low Oxygen" signs. Defrost the evaporator(s) and fully open the porthole before initiating the purging process. Nitrogen should be injected into the room near the evaporator and all fans should be turned on to facilitate mixing. Make absolutely sure that the hallway space near the CA room porthole is well ventilated and that people are kept out of the area while purging is taking place. The cool, oxygen depleted effluent gas from the CA room may pool in the hallways, analysis rooms, loading docks, etc. and there may not be enough oxygen present to sustain human life. When the desired atmosphere concentration is achieved and the room pressure has dropped to near zero, close the porthole and continue to ventilate the hallway areas.

Air Separators

Air separators are now widely used to establish the low oxygen atmosphere and to a lesser extent for scrubbing CO₂ and maintaining the atmosphere in leaky or partially empty CA rooms. The same precautions associated with liquid nitrogen should be followed when purging with an air separator. Gas from an air separator will not cause freeze damage but it can over pressurize the CA room or cause asphyxiation. The oxygen-rich effluent from the air separator should be vented out doors and away from equipment.

The quantity of purge gas and rate of oxygen depletion during purging depends on the capacity of the air separator and the purity of gas being delivered. In Table 2, the quantity and purity of purge gas needed to achieve various storage atmospheres is shown. A lesser quantity of a purer gas is needed to achieve the same final oxygen level in the CA room. However, the cost of producing the purer gas is higher and the delivery is lower than for the less pure gas. In addition, because all air separators deliver higher capacities at lower purities, it is possible to achieve faster pull down rates at certain stages of the process by using a less pure gas.

All air separators have a unique output rate versus purity relationship making it impossible to accurately generalize the performance of all these systems. The manufacturer should be able (and willing) to specify in writing exactly what their machine will do for you. All air separators deliver less gas per hour as the purity of the gas increases. Typically, atmosphere establishment with these machines is faster if you start the purging process on a room at 21% oxygen with an air separator purity setting in the 95 to 96% nitrogen range and then increase the purity to 98% when the room oxygen has dropped below 10%. If you are purging to a final concentration below 5% oxygen, it is generally most efficient to change the purity setting from 98% to 99% when the room oxygen reaches approximately 5.5%. The optimum set points are unique to each machine, and if the manufacturer has other recommendations, follow those instead.

With the electronics available today, I cannot understand why the manufacturers do not simply add a $25 microprocessor to their control panel to provide the optimum purity during the entire purging process. Aside from faster atmosphere establishment, you will save money on electricity by making the indicated manual adjustments.

Separator Configurations:

In the past some growers experimented with returning the vent gas from the CA room to the air separator intake. Where the distances were short this could be accomplished without causing excessive back pressure in the CA room. The lower oxygen in the vent gas improved the separator efficiency, although considerable fresh air still had to be fed into the compressor along with the effluent from the CA room. Several years ago one of the air separator companies patented this process and it is now illegal to configure air separators in this manner.

To my knowledge, you can still legally "cascade" two rooms when using air separators or liquid nitrogen to establish the atmosphere. The output of one room is fed into the second CA room the begin the purging process. This procedure is also helpful in situations where harvest rates briefly exceed machine capacity. If machine capacity is constantly lagging, it would be wise to purchase some nitrogen to permit rapid CA establishment in all rooms.

Several people have called me over the past year to inquire about on site storage of nitrogen from their air separators. While this is an appealing concept, it is a very difficult thing to do on a large scale in a practical way.
If you require small quantities of nitrogen for purging carbon scrubbers after the regeneration cycle, then a tank with a capacity of several hundred cubic feet will suffice. This quantity of low pressure gas will supply the CO2 scrubber for several hours, and will prevent the air separator from "short cycling" each time the CO₂ scrubber is regenerated. Larger quantity storage is more difficult, especially if one wishes to have enough reserve gas to purge a CA room.

The situation is best examined in light of the information in Table 2. It requires from 2,415 to 2,775 cubic feet of 99% and 98% purity nitrogen respectively, to purge 1000 bushels of storage capacity down to 5% oxygen. A 10,000 bushel CA room would require roughly 25,000 cubic feet of nitrogen. In terms of volume, this is approximately equal to the empty volume of a 10,000 bushel CA room. Since the nitrogen from the air separator is produced at a relatively low pressure (5 to 6 atmospheres), the storage vessel(s) have to be large to accommodate significant volumes. (At 5 atmospheres of pressure, the 25,000 cubic feet would fit into a space 1/5th the size of the empty 10,000 bushel CA room.) Higher pressure storage would require robust tanks and booster pumps to compress the gas. While these things are all technically feasible, they are not cost efficient in a one time use per season application.

Storage Tips

Respiration: The respiration rate of apples at 40°F is double that at 32°F. This fact underscores the need for rapid cooling at harvest. This also means that if temperatures are not closely maintained, significant deterioration can occur during long term storage. Store all varieties at the safe recommended temperature and make sure the temperature is being accurately maintained. Do not store chill-sensitive varieties at colder than recommended temperatures.

Leak tests: All CA rooms should be leak tested to insure gas tightness. One of the recommendations for successful CA is a pressure test standard whereby the room loses half of its pressure in 20 to 30 minutes. We suggest starting from a positive pressure of one inch water column and recording the time it takes to reach one-half inch. This should take at least 20 minutes. The starting pressure may be less than one inch, but the time to reach half the starting pressure should still be 20 minutes.
In some cases rooms may test less than 20 minutes and still function satisfactorily. We recommend 20 minutes because this gives a factor of safety and rooms always tend to get less gas tight with age and abuse.
Some growers expressed concern about testing metal clad "tin rooms". They feel one inch of negative pressure could loosen the metal from the walls in old rooms. If the metal and the fasteners have seriously deteriorated this could happen as an alternative test we recommend using less pressure, e.g. 0.3 to 0.4 inches of water column when testing these room under "vacuum". This is sufficient pressure to use
soap solution to find small leaks that do not make audible noise.

Storage Trivia

'Soap': 'Soap' solution for leak testing CA rooms can be improved by adding glycerin to the detergent-water mixture. The glycerin creates a stronger bubble that persists longer and is more visible. Add the same volume of glycerin as dish detergent to your solution. This may be brushed or spritzed on the areas being tested. This solution will wash off easily with water.

Voids: Fully loaded CA rooms actually contain more voids than solids. A 20 bushel hardwood bin occupies about 34 cubic feet of space in the CA room. There is about 3 cubic feet of solid wood in the bin and the 20 bushels of fruit displace about 17 cubic feet. The total solids volume of the bin plus the fruit is approximately 20 cubic feet, or one cubic foot of solids inside the room per bushel. The volume of most CA rooms ranges from about 2.1 to 2.6 cubic foot per bushel of capacity. This means there are somewhere between 1.1 to 1.6 cubic feet of empty space for every 1.0 cubic foot of solids inside the filled CA room.

Acknowledgements

Many growers and storage operators contributed fruit and allowed us to obtain data from their storage and packing operations. Special thanks go to Walt Blackler and Bob Rigdon at Apple Acres who allowed us to obtain much of the data on forced air cooling in their facility. The Statewide Program Committee Research/Extension Grants program has funded the temperature project. Thanks also to Bill Gerling at Lake Ontario Fruit for assisting with commercial-scale trials of Decco I-182. Tom Clark assisted with collection of temperature information. We thank Jackie Nock and Melany Budiman (Ithaca), and Fritz Meyer, Catherine Ahlers and Albert Woelfersheim (Hudson Valley Lab.) for excellent technical assistance.