From the University of Utah
Used with permission
[This paper was written in the late 1980's.]
Two methods of storing dry foods under carbon dioxide were compared.
Method 1: Place 10 grams (A piece having about the same volume of 1 tablespoon.) of dry ice per gallon of container volume into the chosen container. Fill the container, pouring the dry food on top of the dry ice. Set the lid on top of the container so that air currents will not carry away the carbon dioxide gas released from the dry ice. After two hours of venting, seal the container. The amount of dry ice recommended is adequate to completely fill the container with gaseous carbon dioxide. In areas of high humidity, wipe away the whisker growth of ice crystals on the dry ice just before putting it into the container. Do not seal the container before all of the dry ice has sublimed into the gas.
Method 2: Place one pound of dry ice per eight gallons of container volume into a plastic bag. Tie the plastic bag securely to a tube. When carbon dioxide gas flows from the tube, fill a container with carbon dioxide. The flow of carbon dioxide and the fill of the container may be checked with a burning match or candle. Carbon dioxide will extinguish the flame. Carefully and slowly add the dry food to the container, avoiding air currents which will replace the carbon dioxide. When the container is full, slowly withdraw the tube and immediately seal the container. A convenient tube may be obtained from an automotive store as 1/4" or 3/8" flexible fuel line. The flow of carbon dioxide may be speeded up by placing the plastic bag into warm water.
Procedure: Wheat and flour were treated by each method of five-gallon plastic containers with press-top lids and in No. 10 cans with sealed lids.
The five-gallon plastic containers were equipped with a serum of bottle caps. The container cap of flour treated with dry ice was entered with a 23 gauge syringe needle connected to a 3mm I.D. rubber tube. The end of the tube was immersed to a depth of 1-2 mm in soapy water. With the lid pressed into place the tube was the only escape for the gas. Wheat in no. 10 cans with dry ice were sealed after 15, 30, and 60 minutes. The level of carbon dioxide in the containers after 48 hours was estimated by measuring the amount of oxygen with an oxygen electrode. The electrode was adjusted to give a reading of 100%. Readings obtained from the electrode then indicated the displacement of air from the container. The percent of carbon dioxide was calculated as (100 - electrode reading.) The plastic containers equipped with serum bottle caps were penetrated with a 20 gauge 1" syringe needle to obtain a sample of gas from the container. The metal cans were penetrated by a 14 gauge 1" syringe needle.
A sample of flour was taken 48 hours after sealing from a no. 10 can representing each treatment.
Table 1 Carbon Dioxide Content Inside Containers of Wheat and Flour 48 Hours After Treatment Container Product Treatment % CO2 5 Gal Plastic Wheat Dry Ice 36% CO2 Gas 20% Flour Dry Ice 49% #10 Cans Wheat Dry Ice 15 Min 62%* 30 Min 76% 60 Min 89% CO2 Gas 40% Flour Dry Ice 53% CO2 Slow 21% Addition C02 Fast 5% Addition
*The can sealed after 15 minutes of venting was extremely bulged and apparently leaked. The cans vented for 30 minutes were slightly bulged as in a "soft swell."
The moisture contents of flour 48 hours after treatments was 12.99% for the dry ice treatment and 12.97% for the CO2 gas. These differences are not significant because the AACC methods claim reproducibility to 0.05%.
Gas escaping from the plastic container equipped with a vent tube was forming a bubble every 1-2 seconds for 1 hour after sealing the lid. Bubbling stopped between 1.5 hours and 2 hours after sealing the lid.
Conclusion: Both methods are capable of giving carbon dioxide above 10% which is adequate to kill insects by inhibiting aerobic respiration. The food must be added cautiously when using the gaseous carbon dioxide to avoid displacing the carbon dioxide with air.
There was no evidence of injury to the food by direct contact with the dry ice, and no evidence that the method adds moisture. The cans were treated on a rainy day with the humidity near 100%, thus conditions were such as to maximize the risk of adding moisture. When using dry ice, it appears that there would not be any advantage to using greater amounts because a 1 volume displacement seems very adequate. The container must not be sealed before the dry ice has sublimed. When using the recommended amounts of no.10 cans, the dry ice will sublime with one hour. When using the larger amount as required by the 5 gallon plastic containers, the lids should not be sealed for two hours.