Factor #1: The Temperature   Temperature has more to do with how long well dried foods store than anything else. The USDA states, "Each 5.6 C. (10.08F) drop in temperature doubles the storage life of the seeds." Obviously, there is a limit as to how far this statement can be taken. However I expect it basically holds true from room temperature down to freezing. No doubt, the inverse could also be considered true. "Each 5.6C. (10.08F) rise in temperature halves the storage life of seeds." This theory holds true for non-garden seeds as well.
Storage Life Differences Depending on Temperature
                     Constant Storage   Storage life
                     Temp in degrees F    In Years
                     ----------------   ------------
                            37.6  -   -   -  40
                            48.4  -   -   -  30
                            59.2  -   -   -  20
                            70.0  -   -   -  10
                            80.8  -   -   -   5
                            91.6  -   -   - 2.5
                           102.4  -   -    1.25
Note: the above chart is not for a specific food but shows the relationship between temperature and storage life.
The bottom line is even with the very best packaging methods, if you are planning on storing your food in a warm environment, it will only last a fraction of the time it would last if stored in a cool, dry place. It is important you also find a place where the temperature remains constant. Frequent temperature changes shorten storage life. If you don't have a cool place for your food storage, plan on rotating your storage quickly enough to prevent food loss. Factor #2: Product Moisture Content By looking at the USDA nutritional tables, dry beans, grains, and flours contain an average of 10% moisture. Although it is very difficult and unnecessary to remove all moisture from dry foods, it is imperative that any food be stored as dry as possible. Foods with excess moisture can spoil right in their containers. This is an important consideration when packing food with dry ice as moisture condenses and freezes on the outer surface of the dry ice. For long term storage, grains should have a moisture content of 10% or less. It is difficult to accurately measure this without special equipment. Factor #3: Atmosphere the Product is Stored in Foods packed in air don't store as well as in oxygen free gasses. This is because air contains oxygen which oxidizes many of the compounds in food. Food storage companies have a couple of different processes for removing the oxygen:
  • Displacing the oxygen: This is done by purging out all the air in the product with an inert gas. Nitrogen is almost always used because it is the most inert gas known. People doing their own packing occasionally use dry ice which gives off carbon dioxide gas, and probably works just about as well.  Rainy Day Foods/Walton Feed no longer use this method as the oxygen absorbers do a better job.
  • Absorb the oxygen: Oxygen absorber packets do just that. Air contains about 78% nitrogen and 21% oxygen, leaving about 1% for the other gasses. If the oxygen is absorbed, what remains is 99% pure nitrogen in a partial vacuum.
Using oxygen absorber packets ensure  a longer storage life.   Once an absorber is placed in a container,  the container needs to be airtight.   The absorber will then do the job of taking up all the oxygen and leaving it with just nitrogen.   Obviously, your product will be oxygen free under these circumstances.   Buckets should have good gaskets in the lid and even better use a mylar bag on the inside of the bucket.   Cans should have a good seam that will not allow air to pass through.   These absorbers are not intended to use with glass bottles which can not be air tight and allow light in.   Mylar bags require a good seal while other types of bags may "breathe"  too much to keep it airtight. Factor #4: The Container the Products are Stored   To get the best storage life out of your product it must have a hermetic (air tight) seal. Containers that do this well are
  • #10 Cans
  • Seal-able food storage buckets
  • Seal-able food quality metal or plastic drums.
Whatever container you use, be sure it is food grade as your product can be tainted with whatever the container is made from. Plastic sacks are not good air tight containers, for even if they are sealed, the relatively thin plastic 'breathes,' allowing air to pass through. Paper sacks are of course even worse. There is some concern as to how good a seal is made by the lids on plastic buckets used by food storage companies. Manufacturer studies show an extremely small amount of air transfer. This amount is so small, however, that it can be considered a hermetic seal. It has also been found that the lids can be re-used several times without dramatically degrading the performance of the seal. People who purchase products from food storage providers are often concerned about receiving their buckets bulging or with one side collapsed in. Collapsed buckets occasionally occur when ordering from Rainy Day Food's  as the elevation of their packing facility is above 6,000 feet. As the buckets are shipped to a lower elevation, the increased ambient air pressure can sometimes push in one side. If a side is popped in, it is a great indication that the bucket is indeed sealed. And this also holds true for buckets that might be under a slight amount of pressure. If you have purchased a super pail (one that has a mylar bag inside the bucket), crack the lid to equalize the air pressure. You can do this without degrading the storage ability of the product within the bucket as the mylar bag is sealed with the product and absorber.   Remember to re-seal the lid after doing this. Bulging cans: Some bulging cans have been returned to Rainy Day Food's. In almost every case, these cans held mixes that contained baking powder or soda. These cans were sent off for bacteria analysis and came back negative. It is believed that occasionally the extremely small amount of moisture found in the product interacts over time with the baking powder or soda and creates a small amount of carbon dioxide gas. This information was taken from the original Walton Feed website.