Home Preservation of Dried Foods and Grains
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)
(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 diatomaceous 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
|
O2%
|
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 diatomaceous
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 diatomaceous 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 affects the grain. It probably does not.
Sensory evaluation of the bread gave the
same results as the previous tests.
Table 2. Oxygen content and number of Insects found in
wheat stored for 7 months with saw-toothed grain beetle after different
treatments.
Treatment
|
O2%
|
Insects (all dead)
|
Control (no treatment)
|
15.3%
|
3 adult 3 larva
|
CO2
|
12.2%
|
6 adult
|
Gum
|
6.6%
|
5 adult 12 larva
|
Bay Leaf
|
7.3%
|
5 adult 16 larva
|
D Earth
|
8.4%
|
12 adult 4 larva
|
Oil
|
17
|
8 adult
|
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.
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