Common storage requires rather simple structures and is easy to build. It’s building cost shall be lower than that of other two types of storage facilities. Since the storage is cooled by ventilating natural cool air, electric energy use shall be minimal. Common storage facilities are convenient for use and easy to operate.
The construction cost of cave storage would be fairly high if a thick layer of concrete liner is used. Such liner is necessary in a place like Taiwan where heavy rains and earthquakes are quite common. Once constructed, the structure is durable and requires little maintenance and repair costs, however. Well constructed cave storage facilities can be used for decades or even centuries if without natural or man-made destructive disasters. Cave storage may or may not have ventilation or exhaust fans. Even if fans are used, electric energy use shall be low. Since the cave must be narrow and elongated in shape, it is not convenient for loading and unloading fruits in the storage operation. Therefore, it may not suit for very large volumes of fruit storage.
Refrigerated storage facilities require sufficiently effective insulation and refrigeration machines and equipment. The initial construction cost should be the highest among the three types of storage facilities. The facilities also needs periodical maintenance services and even repairs only professionals can perform. The storage is cooled by mechanical refrigeration which requires a lot of electric energy. In general, the higher ambient temperature the more energy consumption; and the poorer insulation the more energy waste.
Among all three types of storage methods, refrigeration storage has the highest construction as well as maintenance costs and the highest energy use. Cave storage has high construction costs but low maintenance cost and low energy use, while common storage has the lowest costs and lowest energy use.
More Thoughts Concerning Commercial Storage
When selecting a storage method for commercial fruit storage, both technological and economic factors have to be considered. Whenever possible, environment friendliness of the method should also be considered. We therefore should use all of our knowledge about the requirements of the fruits, available technologies, economic feasibilities, and the environment to make a judicious choice.
Storing fruits in cooler locations
In citrus fruit storage under sub-tropical climate, cooling and maintaining coolness in the storage are usually desirable or even necessary processes. It would be wise, therefore, to select cooler locations to store fruits if economically feasible. The cooler the climate, the better chance to utilize cool ambient air in storage. Cooler ambient air also helps reducing the cost of refrigeration when refrigeration is used. That is because less heat energy to be transferred into the storage by means of conduction and convection and therefore less heat energy to be transferred out of the storage by mechanical means.
Most of our ‘Ponkan’ mandarins are grown in the central and southern Taiwan, and most of our ‘Liucheng’ oranges are grown in the southern Taiwan. During the storage seasons (i.e., winter and spring) of these citrus fruits, the ambient air temperature is much lower in northern Taiwan than in the central or southern Taiwan. For instance, when three spots of interest are compared, Miaoli has significantly lower temperatures than Chiayi which in turn has significantly lower temperatures than Tainan (Fig. 9). Miaoli is located in the north and is the place where our experimental cave and common storage facilities are located. Both Chiayi and Tainan are located in the south and are the places where lots of mandarins and oranges are grown. The farthest distance between any two spots of the three is >150 km. When considering other factors, more than half of the population of the main island of Taiwan resides in the northern part and the main south to north highways and railways pass through Miaoli. Wouldn’t it be wise to store at least part of southern grown citrus fruits in appropriate places like Miaoli in the north? This is a good example for studies on selecting cooler places for citrus storage.
Uses of various storage methods in combination
Common storage has virtues of being low cost and environment friendly. Cave storage is also environment friendly but is more costly and more difficult to build and less convenient to use.
Refrigerated storage is most costly among the three storage methods, and it also requires a lot of electric energy consumption which is considered environment unfriendly. Therefore, while selecting a storage method for a predictable lot of fruits, common storage should be considered first followed by cave and refrigerated storage provided that satisfactory storage conditions for the lot of fruits can be met.
Fig. 9. Comparison of ambient temperatures of Miaoli ( ), Chiayi ( ) and Tainan ( ) in the citrus harvesting and storage season of 2007-2008. Based on data published by Taiwan Weather Bureau.
According to our research results and field observations, ‘Ponkan’ mandarins and ‘Tankan’
tangors grown in the northern part of Taiwan may be stored in common storage in the north for 1 to 3 months without severe losses. Cave storage or refrigerated storage may be used for longer periods of storage in order to maintain better fruit quality and to minimize storage disorders.
Common storage in the southern region is less useful for lack of cool ambient air in the region.
Building cave storage in the south may not be advisable either for the same reason. Therefore, southern grown citrus fruits may be stored in common storage in the south for only a short period (1 to 2 months). The fruits may be shipped to the north and stored in either common storage or cave storage for longer periods (2 to 4 months), however. Refrigerated storage can, of course, be built in any region, but is needed only for long terms (4 to 5 months) of storage for Taiwan citrus.
Refrigeration cost would be lower in the north than in the south due to lower ambient temperatures in the former. A good combination of three types of storage facilities, particularly when built in cooler locations, will save money and energy while providing adequate protection for citrus fruits.
References
1. Booth, R. H. and R. L. Shaw. 1981. Principles of potato storage. International Potato Center, Lima, Peru. 105 pp.
2. Cohen, E. 1988. The chemical composition and sensory flavor quality of ‘Mineola’ tangerines.
I. Effects of fruit size and within-tree position. J. Hort. Sci. 63:175-178.
3. Eckert, J. W. 1978. Post-harvest diseases of citrus fruits. Outlook on Agric. 9(5):225-232.
4. Grierson, W. and S. Ben-Yehoshua. 1986. Storage of citrus fruit. In: Wardowski, W. F., S. Nayg and W. Grierson (eds.). Fresh citrus fruit. AVI, Van Nostrand Reinhold Co. Inc., New York.
p.479-507.
5. Grierson, W. and T. T. Hatton. 1977. Factors involved in storage of citrus fruits: a new evaluation. Proc. Int. Soc. Citriculture , Vol. 1. p.227-231.
6. Liu, F. W. 2005. Technologies and strategies for harvesting, quarantine treatment, storage, transportation, and marketing of ‘Ponkan’ mandarin (Citrus reticulata Blanco), Tankan (C.
tankan Hayata), and ‘Liucheng’ orange (C. sinensis Osbeck) targeted for export. Taiwan Agric.
Research Inst. Publication No. 117. p.1-13. (In Chinese with English summary).
7. Liu, F. W. 2009. Development of long-term storage methods for ‘Liucheng’ orange (C. sinensis Osbeck). Proc. Symposium on 2009 Research Achievement of Chung-Cheng Agricultural Technology and Social Welfare Foundation. p.146-170. (In Chinese).
8. Liu, F. W., C. H. Han and Y. C. Liang. 2005. Quantitative changes in each component of quality attributes in ‘Ponkan’ mandarin (Citrus reticulata Blanco), Tankan (C. tankan Hayata), and ‘Liucheng’ orange (C. sinensis Osbeck) during long-term storage. J. Chinese Soc. Hort. Sci.
51:217-228. (In Chinese with English abstract).
9. Liu, F. W., C. H. Han and Y. C. Liang. 2005a. Effect of humidity in long-term storage on losses of weight by ‘Ponkan’ mandarin (Citrus reticulata Blanco), Tankan (C. tankan Hayata), and
‘Liucheng’ orange (C. sinensis Osbeck). J. Chinese Soc. Hort. Sci. 51:295-304. (In Chinese with English abstract).
10. Liu, F. W., M. H. Lu and Y. T. Wang. 1997. Development of improved storage methods for
‘Ponkan’ and ‘Tankan’ mandarins and ‘Liucheng’ orange. Proc. Symposium on Post-harvest Handling and Marketing of Horticultural Crops. Taiwan Agric. Research Inst. Special Publication No. 60. p.20-37. (In Chinese with English summary).
11. Liu, F. W., C. H. Pan, S. M. Hsueh and T. H. Hung. 1998. Influences of maturity at harvest and storage temperature on the storability of ‘Ponkan’ mandarin (Citrus reticulata Blanco). J.
Chinese Soc. Hort. Sci. 44:239-253. (In Chinese with English abstract).
12. Liu, F. W. C. H. Pan and T. H. Hung. 1998. Influences of harvesting date and storage temperature on the quality and storability of tankan (Citrus tankan Hayata). J. Chinese Soc.
Hort. Sci. 44: 253-263. (In Chinese with English abstract).
13. Liu, F. W. T. T. Wang and C. H. Pan. 1998. Maturity characteristics of ‘Ponkan’ mandarin (Citrus reticulata Blanco), Tankan (C. tankan Hayata) and ‘Liucheng’ orange (C. sinensis Osbeck) in harvesting seasons. J. Chinese Soc. Hort. Sci. 44:265-273. (In Chinese with English abstract).
14. Site, J. W. and H. J. Reitz. 1949. The variation in individual Valencia oranges from different locations of the tree as a guide to sampling methods and spot-picking for quality. I. Soluble solids in juice. Proc. Amer. Soc. Hort. Sci. 54:1-10.
15. Stewart, I. and T. A. Wheaton. 1971. Effects of ethylene and temperature on carotinoid pigmentation of citrus peel. Proc. Fla. Hort. Soc. 84:264-266.
16. Wells, A. W. 1962. Effects of storage temperature and humidity on loss of weight by fruit. U. S.
Dept. Agric. Marketing Research Rpt. 536. 14pp.