Storage Life of Dry Foods
·*Rotation is a key to wise food storage. If one day a week is set aside to eat from your food storage-your food source would be rotated every 5-7 years.
Introduction
· Four Factors That Effect Food Storage
o Temperature
o Moisture Content
o Container Atmosphere
o Storage Container
Determining the storage life of foods is at best an inexact science as there are so many variables. These range from the condition your food was in when you purchased it, what the food is store in, where it is stored, and the temperature it is stored at. This information is given as a general guide only.
Four Factors that effect food storage:
Long term food storage is best achieved by cool constant temperatures. Optimum conditions are 60 degrees or less. Storage that is done in warmer places will loose some of the nutrition and life span. A constant temperature would be one that doe not have extreme highs or lows. Although not all are able to store at 60 degrees or less, it is important to avoid attics, garages, and storage sheds. They may be cool at nights or on a winter day but daytime temperatures are sure to be warmer. That change daily kills nutrition and taste. Food storage is an investment so it is wise to protect that investment with proper methods. Insulating a closet or small area may be an answer.
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 you may expect it basically to hold true from room temperature down to freezing. No doubt, the inverse could also be considered true. Raising a temperature will half the storage life.
Storage Life Differences
Depending on Temperature
Constant Storage Storage life
Temp in degrees F In Years
---------------- ------------
39.76 - - - 40
49.84 - - - 30
59.92 - - - 20
70.00 - - - 10
80.08 - - - 5
90.16 - - - 2.5
100.24 - - 1.25
Note: the above chart is not for a specific food but shows the relationship between temperature and storage life.
Results of good and poor food storage practices:
An unopened paper bag of white flour which had been stored at 70 degrees F, in a dry climate had been sitting for 3 years in a closet. It made fine looking bread but had such an 'old' and bad flavor that it was difficult to eat. Several years ago a 4 gallon can of wheat that had been stored up high in a garage for about 30 years was used. This came from a part of the country is not as hot as some places, yet in the summers the average garage still gets up into the 90's. Normally wheat will store for 30 years under good conditions yet the bread from this particular wheat did not have a good taste and after a few batches the wheat ended up being thrown away.
Many have long term food storage in basements where the temperatures average around 60 degrees F. Experts give brown rice a 6 month storage life because of all the oils in it that go rancid but some are able to store longer because of the cooler conditions.
Several years ago, Walton Feed was able to test #10 cans that were 30 years old. The basement storage area they came from hovered around 58 degrees F. Benson Lab at BYU did a small evaluation on some of these dehydrated foods. The average oxygen percentage was 8.62%. Ratings according to the following scale were used for grading:
5 = Excellent 3 = Satisfactory 1 = unsatisfactory
4 = Good 2 = Minimum passing
These are the results of that testing:
Headspace Overall
Product % Oxygen Appearance Flavor Aroma Texture Rating
Veg Soup 9.0 3 4 4 4 3
Corn 0.292 3 3 4 2 3
Oats 2.3 4 4 4 4 4
Eggs 2.85 2 2 2 3 2
Dry Milk 20.85 4 4 4 4 4
Milk Solids 20.45 4 4 4 4 4
Butter Powder 4.6 3 3 3 3 3
Alan Wright from Benson Lab, BYU, wrote, “These evaluations are based solely on the products present (after storage) attributes. We did not compare these products against freshly produced counterparts. They were compared with basic standards of food quality. Considering the time period of storage, the products have stored very well (better than many stored that long, i.e. 7 November 1964, 11 August 1967, and 25 July 1970). Most certainly the storage conditions (reduced temperature and reduced oxygen) contributed to this. In general, the products are good and worthy of use. The egg powder would best be used as an ingredient rather than a food itself.”
With Walton’s present packing methods reducing oxygen content to .05%, storage life of present products should be even further enhanced.
These items had a 'good' to 'satisfactory' rating except for the eggs which had a 'minimum passing' rating. After 28 years it is most interesting that without absorbers and modern methods it passed so well.
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. You can expect good storage life if your storage temperature is at 60 degrees F or below. 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. It is also important to know that you can not dehydrate foods at home that reach these levels. Food that is dried to a moisture level of 10% moisture crisply snap when bent. Those of you who dehydrate foods at home know dehydrated foods from your dehydrator are quite pliable when bent, especially fruits. These will not store well for long term storage.
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. Bacteria, one of several agents which make food go rancid also needs oxygen to grow. 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.
- 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.
If oxygen absorber packets are used, care must be taken to use a storage container that can stand some vacuum. If it's not air tight, air will be sucked into your container as the oxygen is absorbed, reintroducing more oxygen that must be absorbed. Before long, the oxygen absorbers will have absorbed all the oxygen they can. Obviously, your product won't be oxygen free under these circumstances.
Factor #4: The container the product is stored in:
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 (Use only cans that are enamel lined, otherwise your food flavor will be tainted by the steel it comes in contact with. An enamel lined can also prevents the inside of the can from rusting.)
- Sealable food storage buckets
- Sealable food quality metal (lined) or plastic drums.
Oxygen absorbers also contain a minute amount of moisture to activate the absorber. Sometimes, with the heat generated by the absorber, they can cause sweating. Therefore using glass bottles or Tupper ware type containers are not recommended.
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 Walton'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 either condition concerns you, crack the lid to equalize the air pressure. You can do this without seriously degrading the storage ability of the product within the bucket. Remember to re-seal the lid after doing this by retapping the lid on tightly.
Bulging cans: Some bulging cans have been returned to Walton’s. In almost every case, these cans held mixes that contained baking powder or soda. 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. Oxygen absorbers can also react with the baking powder causing the cans to bulge. These cans have been sent off for bacteria analysis and in each case came back negative for bacteria. These mixes should be used with several years as they are not long term storage.
http://www.ldschurchnews.com/articles/51562/Home-food-storage-lasts-30-years-or-more.html
http://www.backwoodshome.com/articles/tate55.html
http://ndfs.byu.edu/home/Research/Long_Term_Food_Storage_Research/foodstorageresearch.aspx
http://everydayfoodstorage.net/