STORAGE LIFE OF DRY FOODS
In Consultation with Stephen Portela
FOUR FACTORS THAT AFFECT FOOD STORAGE
|Note: this chart is not for a specific food but shows the relationship between temperature and storage life. Let's look at a couple of real life examples of good and poor food storage practices: |
About a year ago we got an unopened paper bag of white flour which had been stored at 70oF, in a dry climate. It 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.
For another example, a couple of years ago in the Puget Sound area we were given a 4 gallon can of wheat that had been stored up high in a garage for about 30 years. This 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. Even though wheat will store for 30+ years under good conditions, the bread from this particular wheat was very bad tasting and after a few batches we ended up throwing the wheat away (something I always dislike doing).
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.
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. As air is sucked into your container as the oxygen is absorbed, it reintroduces 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. Walton Feed gets around this problem with their plastic Super Pail buckets by purging the product first with nitrogen before tossing in the two oxygen absorber packets. This way the absorbers have little or no oxygen to absorb and don't create a vacuum within the pail. As cans work well under a partial vacuum, purging them with nitrogen isn't necessary before inserting the oxygen absorber packet and sealing the lid. Large seeds store better in nitrogen. On the other hand, small seeds, like many garden seeds store better in air. For this reason Walton cans their garden seed packs in air.
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:
Sealable food storage buckets
Sealable food quality metal or plastic drums
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.
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.
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 storageability of the product within the bucket. Remember to re-seal the lid after doing this.
Bulging cans: Some bulging cans have been returned to Waltons. 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.
Hulled or Pearled Oat
The Hard Grains
Soft Grains have softer outer shells which don't protect the seed interior as well as hard shelled seeds and therefore won't store as long. Hermetically sealed in the absence of oxygen, plan on a storage life of 8 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
The Hard Grains all store well because of their hard outer shell which is nature's near perfect container. Remove that container and the contents rapidly deteriorate. Wheat, probably nature's longest storing seed, has been known to be edible after scores of years when stored in a cool dry place. As a general rule for hard grains, hermetically sealed in the absence of oxygen, plan on a storage life of 10-12 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
Hard red wheat
Hard white wheat
Special bake wheat
As beans age they lose their oils, resist water absorption and won't swell. Worst case, they must be ground to be used. Storing beans in nitrogen helps prolong the loss of these oils as does cool temperatures. Hermetically sealed in the absence of oxygen, plan on a storage life of 8-10 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
Black Turtle Beans
Great Northern KidneyBeans
Small Red Beans
Dehydrated vegetables store well if hermetically sealed in the absence of oxygen. Plan on a storage life of 8-10 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
Dehydrated Dairy Products
Dehydrated dairy products generally store very well if stored dry in hermetically sealed containers. Plan on a storage life of 15 years if stored at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures. One exception is Morning Moo. As a new whey based product, it hasn't been tested for long term storage. Plan on rotating this product after 5 years.
Morning Moo Whey Powder
Flours and Other Products Made From Cracked/Ground Seed
After seeds are broken open their outer shells can no longer protect the seed contents and seed nutrients start to degrade. Don't try to store unprotected flours longer than a year. Hermetically sealed in the absence of oxygen, plan on a storage life of 5 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
All Purpose Flour
Whole Wheat Flour
Granola Wheat Flakes
Pasta will store longer than flour if kept dry. Hermetically sealed in the absence of oxygen, plan on a storage life of 8 - 10 years at a stable temperature of 70oF. Pasta should keep proportionately longer if stored at cooler temperatures.
Fruit doesn't keep as well as many dehydrated items. Hermetically sealed in the absence of oxygen, plan on a storage life of 5 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures.
Honey, Salt and Sugar
Honey, salt and sugar should keep indefinitely if stored free of moisture. Watch out for additives in the honey. It is possible to buy honey with water and sugar added. This honey generally doesn't crystallize like pure 100% honey does when stored for a long time. If there are additives, there is no saying how long it will last.
Peanut Butter Powder
Peanut butter powder will not store as long as wheat flour. Hermetically sealed in the absence of oxygen, plan on a storage life of 4-5 years at a stable temperature of 70oF. It should keep proportionately longer if stored at cooler temperatures.
Brown and White Rices
Brown and white rices store very differently. Brown rice is only expected to store for 6 months under average conditions. This is because of the essential fatty acids in brown rice. These oils quickly go rancid as they oxidize. It will store much longer if refrigerated. White rice has the outer shell removed along with those fats. Because of this, white rice isn't nearly as good for you, but will store longer. Hermetically sealed in the absence of oxygen, plan on a storage life for white rice of 8-10 years at a stable temperature of 70oF. It should keep proportionately longer if stored at cooler temperatures.
Seeds or Sprouting Seeds
All viable seeds are hibernating tiny living plants that only need moisture and warmth to sprout. And much like a chick in an egg, all the nutrients this little life needs to spring into existence is contained within it's shell.
Like boiling an egg, heating a seed will kill that little life within it. However, unlike an egg, a seed can withstand cold temperatures. As seeds usually remain edible after the life within it dies, we must use different criteria when determining sproutable seed storage life. And again the big deciding factor is temperature. The big seed companies freeze their seed between seasons to promote long life. Of course, you can also do the same thing. Plan on a storage life of 4 years at a stable temperature of 70oF. They should keep proportionately longer if stored at cooler temperatures. Rita Bingham's Sprouting Book suggests that "Vacuum sealed or nitrogen treated seeds store longest, with a shelf life of up to 15 years." This is presupposing they are kept very cool or frozen.
Alfalfa is a unique seed as it actually germinates better if the seed is 2 or 3 years old. Most any sample of alfalfa contains 'hard' seed and 'soft' seed. Soft seed germinates within two days while hard seed germinates in about a week. The problem is, by the time the soft seed sprouts are ready to harvest, the hard seed may not have germinated yet. As storage time draws on, the hard seed turns into soft seed. Older seed germinates closer together. Stored in good conditions, alfalfa seed should have a good percentage of germination up until it is 8 years old.
Total Vegetable Protein, made from soy beans, has an unusually long storage life. Hermetically sealed in the absence of oxygen, plan on a storage life of 15-20 years at a stable temperature of 70oF. TVP should keep proportionately longer if stored at cooler temperatures.
Yeast, a living organism, has a relatively short storage life. Keep yeast in the original metal foil storage containers. If the seal remains intact, yeast should last 2 years at 70oF. However it is strongly recommended that you refrigerate it, which should give you a storage life of 5 years. Frozen yeast should store for a long time.
All contents © 1996-2000, Al Durtschi. All rights reserved. This information may be used by you freely for noncommercial use with my name and E-mail address attached. Revised: 3 Dec 1996
Al Durtschi, E-mail: firstname.lastname@example.org
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