Vacuum Storage in Plastic Bags. From Teguh Muhammad Sardjono (Indonesia), he informs us that farmers in Indonesia do not store paddy for a long time and face no problems. BULOG however maintains security stocks in a network of warehouses throughout the country. As they store milled rice in bags, insect pest infestation is controlled through regular bag stack fumigation with phosphine, carbon dioxide, or contact insecticides. They are very concerned about storage losses and possible chemical residues. In an article in by J. Sassen in Far Eastern Agriculture, he argues for the technical and financial advantages of vacuum storage in plastic bags (shrink-wrap storage), compared to silo storage technology. The ASEAN Post Harvest seminar participants in Surabaya several years ago will recall visiting the site where BULOG was using the technology. It was reported that over 100,000 tons of brown rice were vacuum stored by BULOG. We would be interested in the technical and economic assessment of this methodology from the user's viewpoint.
Storage in Plastic Enclosures. At a smaller scale, a request came in from IRRI's man, Keith Fahrney in Laos for a 10 ton paddy storage recommendation. One of the possibilities is the sealed plastic enclosure developed by NAPHIRE with assistance from ACIAR and Israel. When last evaluated, the technology had problems including: moisture condensation on the top layers and rodents coming through the plastic sheets. We got an immediate response from Jan Van Graver (CSIRO, Australia). He states that condensation is minimized if the plastic cubes are well sealed and are placed in the shade. Further, rodent penetration can be overcome by ensuring that the plastic sheeting forming the side-walls do not droop to the ground. If the walls are sheer and do not provide a hiding place for rodents there will be no penetration. Alternatively, Van Graver stated that the enclosures could be built over a foundation made of rice hull. This is similar to the volcani cubes developed in Israel. Drs Jonathan Donahaye and Shlomo Navarro report that they first tried out the plastic storage cubes in Sri Lanka to enable a cooperative to control prices at the farm gate. They reported that this storage method protected the paddy for at least 3 months. The two scientists confirm that moisture condensation in outdoor storage is intense in extreme temperature gradients. Moisture condensation is confined to the top layers. Placing the cubes in the shade prevented moisture condensation, according to the Australian - NAPHIRE experience. Further information on enclosure storage can be obtained from the Department of Stored Products, Agricultural Research Organization, Bet Dagan 50-250, Israel, or BUPRE (formerly NAPHIRE) Munoz, Nueva Ecija, Philippines.
While this technology is being refined, we recommend that Keith Farhney use barn storage, or the paddy granary used in Central Thailand. This is an elevated wooden bulk bin with rodent guards. They have abundant good lumber in Laos, and Thais have been using paddy granary as long as they can recall. Insect infestation can be a problem if paddy is stored over 3 months, but there are ways to control them.
Bulk Storage Systems for Asia. Bulk systems allow more efficient handling within the processing plant, and better pest control. Stored grain is a living, breathing seed that generates heat. In cases of insect infestation, the respiration of the insects creates hot spots. Hot spots create vapor pressure differentials and convection currents resulting in moisture migration from hot to cold spots, accelerating heat generation. If left uncontrolled, the wet grain will rot. Management of bulk systems requires aeration with dry air. In the tropics, aeration can only be done when the relative humidity of the air is below the equilibrium level of grain measured at 14% wb. Aeration with humid air remoisturizes the grain, causing fissures in the paddy.
We had the opportunity to develop specifications for a bulk storage and handling system for a client company in Bukidnon, Philippines. The aspect of bulk storage in a corrugated metal silo outdoors for corn is the same as for paddy, with the exception that corn is soiled with debris from bees-wings. Norman Teter (retired extension engineer, University of Nebraska) had ascertained that in the tropics a larger aeration fan is needed for a shorter time. Using the computer programme developed at UNSW by Dr Driscol's group, Justin Tumambing (NAPHIRE) was requested to input the weather data in Mindanao, and he derived an airflow-rate 4 times the norm specified in the US. This confirmed Norman Teter's estimate and inferred a much bigger aeration blower with a higher horsepower motor. There has been difficulty experienced in Southeast Asia with the use of outdoor silos including the problem of grain rotting in the sides, the top and in the bottom of the silo. Rotting in the bottom of the silo may be explained by moisture migration. Wetting in the top and sides comes from moisture condensing on the grain. Apparently when the air space underneath the roof is heated during the day, the relative humidity drops and the grain absorbs a lot of moisture which condenses when it gets into contact with the cold metal roof early in the morning. Water has been seen streaming from under the roof to the side walls wetting the grain. This phenomenon was eliminated with two exhaust fans to evacuate the air space underneath the roof at night. Apart from this, the technicians were instructed to strictly follow aeration guidelines set for them. There has been no report of spoilage yet.
In a recent interview of a rice miller in the Philippines, he was asked for his wish list for improving operations. His priority was bulk handling and storage. He was paying PHP1.00 (US$0.03) for every movement of a 50 kilo bag, and there are 10 movements in the plant as the grain is dried stored milled and transferred. Research and pilot systems have to demonstrate that bulk systems technology is feasible in the tropics, if only to be able to control pest infestation and increase labor productivity.
Passive Aeration. Dr Maitrie Neubanij (Post Harvest Section, Thailand) tried to induce passive aeration by installing perforated pipes vertically in a metal experimental silo. He observed no temperature gradients in the pipe to induce a chimney effect, with no effect on the heating of the grain near the walls on the east and west sides of the silo. This is highlighted here, as it is commonly thought that inserting pipes in a bin can provide the required air movement to neutralize the effect of solar heating, the heat of respiration of grain and insects, and prevent moisture migration.
Refrigerated bulk storage. A European designed system in Thailand used refrigerated bulk bins for storing paddy. It is rumored that the system has been discontinued. A possibility is when the cold grain is withdrawn from the silo in humidity, moisture can condense on the grain. In a visit to Taiwan, the corrugated sheet metal silos of a farmer's association was insulated. Refrigerated air (perhaps with some reheating) was being pumped into the silo. It was difficult to obtain details from the owners and the economist. Refrigerated systems for bulk storage of paddy are being promoted in Asia, and more information is needed.