When low moisture, low-fat dry foods are purchased in large quantities, they must be stored properly to remain edible and pest free. One method of storage is to use dry ice in HDPE plastic buckets.
Buckets should be opaque. Use food-grade plastic buckets with gaskets in the lid. Never use buckets that have held anything but food.
Dry ice is solidified carbon dioxide. Care should be taken when handling it to avoid burns. Hands should be protected by cloth or leather gloves, or folded paper when handling it. Search the internet for local sources of dry ice.
At room temperature, dry ice will sublimate, or turn to gas, from its solid form. When dry ice is placed in a container of food, the resultant carbon dioxide forces the oxygen and free moisture out of the container. The remaining atmosphere suffocates insects but does not usually kill insect eggs in the food. If the container is kept sealed and airtight, the carbon dioxide will remain, and the eggs will not hatch. Over time, the eggs may die. Repeated openings of the container will allow air and moisture to return and eggs may then hatch.
When treating dry foods with dry ice, approximately 12 ounces of dry ice is required for 100 pounds of grain – 4 ounces per 5-gallon bucket or 6 ounces per 6-gallon bucket.
To treat dry foods in plastic buckets:
- Place 2 to 3 inches of food in the bottom of the bucket.
- Wearing gloves, wipe frost from the dry ice using a clean dry towel.
- Place dry ice in the center of the bucket on top of the food.
- Pour food over the dry ice to within 1 inch of the top.
- Loosely attach the lid.
- Wait at least one hour or until the bottom of the bucket is no longer very cold before sealing the lid on.
- Secure the lid tightly.
- If the bucket lid or sides begin to bulge after a short time, “pop” the lid. Do not allow the gas pressure to remain.
- When the bucket no longer bulges, it is safe to store.
- Be sure the bucket lid is on tightly before it is stored, or carbon dioxide will be lost and replaced by air (oxygen and nitrogen).
Avoid placing dry ice directly on plastic. The extreme cold could cause the plastic to become brittle and crack. Also, do not use glass containers. The pressure of the gas could cause the glass to shatter.
Buckets should not be stored directly on cement. They should rest on racks or pieces of wood to allow air to circulate underneath and prevent the cement from sweating. Avoid stacking them more than 3 high especially without boards between the layers or the center of the lid may crack and break.