Home Preservation Of Dried Foods And Grains

From the Benson Institute Review, Winter 1984 pp. 19-20, BYU
Used with permission

By Dr. Albert E. Purcell, Research Associate, Department of Food Science and Nutrition, Brigham Young University
(Preliminary report of research on home storage of grains and dried foods)

Grains and dry foods may form a basis for food storage programs, These products are not subject to microbial or fungal attack, but both are subject to infestation. The infestation may be in the product either as live insects or insect eggs at the times of procurement, or the stored products may become Infested during storage. The latter may be prevented by selection of proper containers.

Containers selected for storage of grains and dried foods should have a tight seal that will not allow passage of tiny larva of the pests which may infest dried foods. These pests, either larva or adult, are capable of penetrating thin plastics. This eliminates the use of plastic bags or thin plastic containers. Heavy plastic, 5 gallon containers appear to resist invasion, but if rodents are a problem, rats and mice can penetrate them.

Glass containers with hard plastic or metal lids are excellent storage containers if they can be stored without the possibility of breakage. Containers may be toppled from a shelf and be broken or crushed by debris as a result of earthquakes or other structural damage. Metal cans are the most suitable storage containers. They are resistant to insects and rodents. They may be dropped and rather severely crushed without contaminating the contents or even breaking open. Storage in metal containers allows only one possibility for infestation and that is that the grain or food is infested at the time it is put into storage.

When preparing food for storage, it is prudent to use some treatment detrimental to insects or insect eggs in the product. There are presently as many recommendations for this as there are for curing warts, and many testimonials about effectiveness. Most grains and dried foods are not infested at the time of storage and any successful storage of such products becomes a testimonial to the effectiveness of the method used. We have devised a number of experiments to test the effectiveness of various methods of preparing grains and dried foods for storage in sealed cans.

In one experiment, soft wheat with a moisture content of 12.3 percent was placed in size 303 metal cans with 8 live powder post beetles. Four cans were treated by one of each of the following methods: carbon dioxide (dry ice), spearmint gum, freezing, bay leaf, and diatomacious earth. The cans were stored at 70 degrees Fahrenheit plus or minus 5 degrees. At the end of the storage period, oxygen content of the cans was determined, Cans were opened and the number of insects were counted and the amount of damage rated subjectively. Germination of the wheat was tested. The wheat was cleaned, ground to whole wheat flour and made into bread rolls, The rolls were evaluated by a taste panel.

No live insects were found, as shown in Table 1. If it is assumed that the oxygen loss could be counted as carbon dioxide, it appears that the insects were killed by an increase in carbon dioxide before completing a reproductive cycle. The finding of more adults than were added suggests that eggs or young larva had time to mature.

Table 1. Oxygen content, insects found and subjective evaluation of wheat infested with powder post beetles and stored 245 days after treatment.

Treatment %02 Insects Remarks Control (no treatment) 18.4 8 dead adults Hollow kernels & powder CO2 12.4 8 dead adults No hollow kernels Gum 16.4 8 dead adults Hollow kernels & dust Freezing 19.1 8 dead adults No hollow kernels Bay Leaf 11.3 11 dead adults Numerous hollow kernels D Earth 7.5 10 dead adults Numerous hollow kernels. The presence of hollow kernels suggests that the insects were able to damage some wheat in the samples treated with spearmint gum, bay leaf and diatomacious earth.

The wheat was tested for germination and there was 100 percent germination in all samples, The wheat was not damaged by any of the treatments. Sensory evaluation of the bread indicated there was no significant difference in the quality of flavor, but a number of panelists detected a spearmint flavor in the rolls made from wheat treated with gum.

A similar test was repeated with the saw-toothed grain beetle using the same variety of wheat at 13.3 moisture. These samples were stored 198 days. The freezing treatment was omitted because of its previously proven effectiveness. An oil treatment was added. Again in this test, no live insects were found, as shown in Table 2.

The oxygen levels were lower and all cans had some grains that had tiny sprouts. Control, bay, gum, and diatomacious earth had some larva, suggesting that some eggs or small larva were added with the adults. There were fewer hollow kernels, suggesting that the insects had less time to damage the wheat, because the higher respiration rate of the more moist grain increased C02 concentration faster.

There was 100 percent germination in all samples except the one with the gum. This observation has not been repeated, thus it cannot be concluded that gum adversely...

Table 2. Oxygen content and number of Insects found in wheat stored for 7 months with saw-toothed grain beetle after different treatments.Treatment %02 Insects (all dead) Control 15.3 3adult. 3 larva 002 12.2 6 adult Bay leaf 73 5 adult. 16 larva Gum 6.6 5 adult. 12 larva D. Earth 8.4 12 adult. 4 larva Oil 17.0 8 adult ...affects the grain. It probably does not.

Sensory evaluation of the bread gave the same results as the previous tests.

A test with the saw-toothed grain beetle was set up using cans with a thin press top plastic lid. The wheat for this test had been frozen previously to kill all the insects and eggs. One sample was set up with no added insects. The cans were all stored in the same cardboard box. At the end of one year, all samples were so heavily infested that no counts were made. The oxygen content of the cans was near that of air.

The main conclusions drawn from these tests is that infestations in hermetically sealed containers are self-limiting due to generation of carbon dioxide by the respiring grain [and insects]. Plastic lids do not provide an adequate barrier to prevent re-infestation. Unless there is good reason to believe that the grain is completely free of infestation, the grain should be treated by freezing to -10 degrees Fahrenheit (-23 Centigrade) at the center of the container for 2-4 hours or with carbon dioxide according to the following procedure: Place dry ice into the container (l oz./gal. or 2 gm./liter) and fill the container with wheat. Set the lid in place but do not seal. When the frost that formed on the bottom of the container has melted, seal the container. If the container is sealed before the dry ice is gone, the container may burst.

Chemical treatment of wheat with malathion, ethylene dichloride, or ethylene dibromide has been used very successfully for a number of years, but now that analytical methods have been refined to detect minute quantities of residues, the use of these chemicals by the U.S. Food and Drug Administration has been declared harmful and is therefore not recommended.

The Benson Institute welcomes articles from scientists concerning agriculture, food storage, and other related topics. Please send articles to The Benson Institute Review, 8-49, Brigham Young University, Prove, Utah 84602.