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I've been looking all over for the optimum humidity or % of humidity for a long-term storage pantry or locker. I've searched for specifics but can't find anything. I read one article that says 50% to 60% humidity but that seems way too high. I'd think that would be rusting cans and breaking down packaging.

I know the ideal moisture content of rice, grains, beans and etc. should be 10% before Oxygen-free storage just not sure about the storage room.

I live in Florida and I'd like to know if I should use a humidifier.

Does anyone know of a scholarly article on the subject?

Regards, Scott
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For already packaged materials that should not be an issue. Radical temp swings will do more damage as it will cause items to condensate on the external packages. Light and heat are main contributors to extending viability on sealed product. Well ventilated areas will keep buildup down. I leave unpackaged product I dehydrate for days in my dehydrator for thinks like crackers and chips if I want to keep them crunchy for snacking.

I have cans that are over 10 years old in my garage in the PNW with no issues to rust.
 

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For already packaged materials that should not be an issue. Radical temp swings will do more damage as it will cause items to condensate on the external packages. Light and heat are main contributors to extending viability on sealed product. Well ventilated areas will keep buildup down. I leave unpackaged product I dehydrate for days in my dehydrator for thinks like crackers and chips if I want to keep them crunchy for snacking.

I have cans that are over 10 years old in my garage in the PNW with no issues to rust.
Copy That. I'm on a mission 😅
 

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Discussion Starter #5 (Edited)

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I've been looking all over for the optimum humidity or % of humidity for a long-term storage pantry or locker. I've searched for specifics but can't find anything. I read one article that says 50% to 60% humidity but that seems way too high. I'd think that would be rusting cans and breaking down packaging.

I know the ideal moisture content of rice, grains, beans and etc. should be 10% before Oxygen-free storage just not sure about the storage room.

I live in Florida and I'd like to know if I should use a humidifier.

Does anyone know of a scholarly article on the subject?

Regards, Scott
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So it sounds like you are asking two things.

1) relative humidity to avoid corrosion of cans

2) relative humidity for storing unsealed dry goods( I think we can accept that if the cardboard is falling apart from moisture, it’s too humid for long term storage.

For 1) I don’t thInk there is much of an issue, away from the coastline, until you get condensation . If the can is below dew point, mosisture will condense on the can. And you will likely get corrosion over time. For example a basement or root cellar at 60 degrees, that is exposed to outside air at 80 degrees and 40% RH will get condensation on the cold can surfaces until they warm up, or enough moisture is lost to condensation. Here in the south, it’s a good approximation that the morning low is equal to the dew point ( it’s certainly not much less). If your basement/ root cellar is cooler than the morning lows, you may get condensation.

Fo 2)) the easy answer is long term storage should be sealed. But to answer you question you have to calculate based on air exchanges and moisture equilibrium curves- the latter can be found in the ASAE handbook (American Society of agricultural engineers, now ASABE, Agricultural and biological engineers) For grain bins they may slowly gain or loose moisture, but it’s usually safely ignored. For a one lb box of rice,it’s going to track the average relative humidity ( but you need the ASAEdata to figure equilibrium moisture content vs RH). And you need to know the preferred storage moisture content- it Varies based on product.

BTW, may basement is kept at 58% RH, never had a problem with rust on cast iron machined surfaces, much less cans rusting or cardboard falling apart. There’s 76 c/s of MH and maybe 20 cases of other #10 cans down there.

Don’t confuse Relative humidity with moisture content. The two reach an equilibrium over time, but are not equal.
 

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My food storeroom is at about 40%. I've had ZERO rust issues, and its nice for storing potatoes and onions etc.

All dry grains are stored in sealed containers.

Condensation only comes from temperature changes. You could have 90% humidity with no surface moisture if the temp was completely consistent. My storeroom is earth sheltered and super insulated and temp only varies on a seasonal basis.
 

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Do not see a specific humidity number at the USU link. Been going thru a lot of other info for our local folks, and my reading shows limiting humidity to around 15% to be the consensus.

Your storage area should be located where the temperature can be kept above freezing and, if possible, below 72º F (22º C). Ideally, your storage area should have a humidity level of 15% or less. Keep containers off the floor and out of direct contact with exterior walls to reduce the chances of condensation brought on by temperature differences between the container and the surface on which it is resting.

As a general rule the storage life of most foods is cut in half by every increase of 18º F (10º C). For example, if you've stored your food in a garage at 90º F (32º C) you should expect a shelf life of about half what could be obtained perhaps in your pantry at 70º F (21º C), which in turn is half the storage life that you could get if you kept it in your basement or refrigerator at 50º F (10º C).
 

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Do not see a specific humidity number at the USU link. Been going thru a lot of other info for our local folks, and my reading shows limiting humidity to around 15% to be the consensus.

Your storage area should be located where the temperature can be kept above freezing and, if possible, below 72º F (22º C). Ideally, your storage area should have a humidity level of 15% or less. Keep containers off the floor and out of direct contact with exterior walls to reduce the chances of condensation brought on by temperature differences between the container and the surface on which it is resting.

As a general rule the storage life of most foods is cut in half by every increase of 18º F (10º C). For example, if you've stored your food in a garage at 90º F (32º C) you should expect a shelf life of about half what could be obtained perhaps in your pantry at 70º F (21º C), which in turn is half the storage life that you could get if you kept it in your basement or refrigerator at 50º F (10º C).
Thanks, I saw 15% in one article but couldn't find a source. Any idea where that number is coming from?
 

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Cannot cite specific sources, been going thru hundred+ food storage documents I have stored.

Overall condition notes:

Food Storage Notes - Just trying to share some notes, so ‘new arrivals” do not need to “re-invent the wheel”.

Your storage area should be located where the temperature can be kept above freezing and, if possible, below 72º F (22º C). Ideally, your storage area should have a humidity level of 15% or less. Keep containers off the floor and out of direct contact with exterior walls to reduce the chances of condensation brought on by temperature differences between the container and the surface on which it is resting.

Pests. There is the chance that items such as grains, beans, powder mixes, etc., if not in air-tight sealed containers, may when purchased contain insects or insect eggs. Heating, freezing, sealing with an inert gas, etc. may kill such. You may also consider food-grade diatomaceous earth.

You may destroy adult insects in foods by placing them in a deep freezer at or below 15° F (-18° C) for 2 to 3 days. This may not kill all the larvae and eggs so repeat this process after a month. All insects, eggs, and larvae will be killed if frozen at 1 0 ° F ( - 2 3 ' C ) for 2 to 3 days.

Insects can be destroyed by heating the internal temperature of a food to 150" F (66° C) and maintaining this temperature for 4 minutes (or 140° F [50° C] for 10 minutes or 120° F [49' C] for 20 minutes). Heating to higher temperatures, or for longer periods of time, will reduce germination and perhaps handling quality of subsequent flours milled from these grains. Note: Home ovens can be used, but their temperature and the temperature of the food need to be checked with mercury thermometers.

Dry ice can be used to kill adult insects and larvae, but it probably will not destroy the eggs or pupae. Pour 2 inches of grain into the bottom of the container. Add dry ice; then fill with grain. Eight ounces (227 g) of dry ice is recommended for 100 pounds (45kg) of grain, or 1 pound (454g) for each 30 gallons (114 liters) of stored grain. Seal the containers loosely for 5 to 6 hours; then seal them tightly. Containers must be air tight and capable of being tightly sealed.

According to the USDA, high-acid canned goods, like tomatoes and citrus fruits, will keep for up to 1½ years. Low-acid canned goods—that’s pretty much everything else, including vegetables, meat, and fish—will last for up to 5 years.

Generic shelf life periods:

Commercially freeze-dried 10 - 15 years
Commercially dehydrated fruits & vegetables 10 years
Home canned products 2 – 5 years
Home dehydrated fruits & vegetables 2 years

As a general rule the storage life of most foods is cut in half by every increase of 18º F (10º C). For example, if you've stored your food in a garage at 90º F (32º C) you should expect a shelf life of about half what could be obtained perhaps in your pantry at 70º F (21º C), which in turn is half the storage life that you could get if you kept it in your basement or refrigerator at 50º F (10º C).
 

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More notes:

Food deterioration. The major causes of food deterioration are microorganisms, action of enzymes, chemical reactions, physical changes, time, and insects and/or rodents, multiple can be operating at the same time.

Microorganisms. Bacteria, molds, and yeasts.

Bacteria. Unicellular microorganisms of many forms. Some bacteria produce spores which are remarkably resistant to heat, chemicals, and other adverse conditions. Bacterial spores are far more resistant than yeast or mold spores, and more resistant to most processing conditions than natural food enzymes. All bacteria associated with foods are small, most are of the order of one to a few microns in cell length and somewhat smaller than this in diameter. (A micron is one-thousandth of a millimeter (0.001 mm) or about 0.00004 inch.) All bacteria can penetrate the smallest of openings, and many can pass through the natural pores of an egg shell once the natural bloom of the shell is worn or washed away.

Yeasts. Somewhat larger than bacteria, of the order of 20 microns in individual cell length and about half this size in diameter. Most yeasts are spherical or ellipsoidal in shape. Fresh vegetables, meat, poultry, and cheese often contain yeasts, but in these foods, bacteria outgrow the yeasts. When bacterial inhibitors are added, yeasts can dominate. Some yeasts are found in foods such as honey, molasses, sugar, and fruit. Salt-tolerant yeasts grow as films on brine food and on salted food and ham.

Molds. Larger than bacteria and yeast, they grow by a network of hair-like fibers called mycelia and send up fruiting bodies that produce mold spores referred to as conidia. The blackness of bread mold and the blue-colored veins of blue cheese are due to the conidia, while beneath the fruiting heads, the hair-like mycelia anchor the mold to the food. The mycelia are a micron or so in thickness and, like bacteria, can penetrate the smallest opening; or in the case of weakened skin or shell can digest the skin and make their own route of penetration.

Enzymes. Organic catalysts which are produced by the cells of animals, plants, or bacteria. Microorganisms possess enzymes which produce fermentation, rancidity, and putrefaction, likewise uninfected food plants and animals have their own enzyme complement. Unless these enzymes are inactivated by heat, chemicals, or other means, they continue to catalyze chemical reactions within foods. Some reactions to some levels are desirable, for example ripening of tomatoes after they are picked and natural tenderizing of beef on aging, but beyond an optimum point it becomes food deterioration.

Chemical. Examples include oxidation, color changes, reactions between a food container and its contents, and
the coagulation of proteins. A rule of chemistry states that for every 18ºF (10ºC) increase in temperature, the rate of a chemical reaction doubles. Applied to foods every such rise in temperature cuts food shelf life by half.

Physical changes. May cause food spoilage, or deteriorative changes such that the food is unsuitable to use. Examples:

Freezing. May cause destruction of emulsions and texture. Products such as salad dressing and mustard, contain a fat/oil and water mixture which does not combine without special processing or additives. When frozen the emulsion is destroyed and the fat and water separate. Fruits and vegetables will have their texture disrupted. Skins will crack, leaving the food susceptible to attack by microorganisms. The texture of canned fruits and vegetables becomes softened and mushy due.

Cold damage. Many fruits and vegetables as living systems have optimum temperature requirements. At common refrigeration temperatures of about 41ºF (5ºC), several fruits and vegetables are weakened or killed. Bananas, lemons, squash, and tomatoes are examples of products that should be held at temperatures no lower than 50ºF (10ºC) for maximum quality retention.

High Temperature. Most food should be stored between 50º-100ºF (10º-38ºC). Excessive heat can denature proteins, break emulsions, dry out foods by removing moisture, and destroy vitamins. Excessive heat in green vegetables causes cell walls and membranes to lose their integrity, acids and enzymes to be released, resulting in soft texture, off-colors and off-flavors. On muscle tissue proteins are denatured, proteins clump, and enzymes are inactivated, resulting in toughening texture, loss of waterholding capacity, cooked or caramel flavors, and development of off-colors.

Dehydration. Meat is 70 to 75 percent water. Fresh fruits and vegetables 80 to 95 percent water. When the humidity is too low in a storage area, dehydration results.

Excessive Moisture. Dried, dehydrated, and freeze-dried foods are very hygroscopic (readily taking up and retaining moisture) & if not properly packaged become lumpy or caked. A slight condensation on a food surface can become a pool for the multiplication of bacteria or the growth of mold. In a moisture-proof package, food materials such as fruits and vegetables can give off moisture from respiration and transpiration. This moisture is then trapped within the package and can support the growth of microorganisms.

Mechanical Damage. Damaged foods are more susceptible to invasion by microorganisms. Cell walls destroyed by mechanical abrasion liberates the inherent enzymes, these can begin deterioration.

Light. Can cause fading of color. Some vitamins are destroyed by light, notably riboflavin, vitamin A, and vitamin C. Milk in bottles exposed to the sun develops "sunlight" flavor due to light induced fat oxidation and changes in the protein. Sensitive foods can be protected by impervious packaging.

Potato warning. After exposure for two days or longer the skin and the flesh may develop chlorophyll and an alkaloid called solanine. The green tubers acquire a bitter, pungent taste. If eaten in quantity, they may be poisonous. Solanine is the bitter and poisonous component. Chlorophyll is tasteless and harmless.

Time. After slaughter, harvest, or manufacture there is a transitory period until the food succumbs to the above deterioration factors. The longer the time, the greater the destructive influences. Certain cheeses, sausages, wines, and other fermented foods are improved with aging up to a point, however, for the vast majority of foods, quality decreases with time, and the major goal of food handling and preservation practices is to capture and maintain freshness. Storage life is determined to a great extent by type of food, method of processing, method of packaging, and storage environment.

Insects & Rodents.

Insects are particularly destructive to cereal grains and to fruits and vegetables. When insects eat they damage the food and open it to bacteria, yeast, and mold infection. Insects are generally controlled in grain, dried fruits, and spices by fumigation with chemicals, the use of which may be prohibited in foods high in moisture because of the possible formation of toxic substances. Eggs may persist or be laid in the food after processing, as for example in flour.

Rodents. They not only consume but contaminate foods with urine and droppings may harbor several kinds of disease-causing bacteria. One rat pill, or fecal dropping, can contain several million bacteria. Even if the pill does not get into food directly, it will become dry and fall apart or be crushed. The particles then may be blown or carried into food.

Pest-proof the building. Deprive pests of food and shelter by following good housekeeping practices. Use appropriate control measures to exterminate pests.

Food is a very complex item composed of many substances, some of which are carbohydrates, proteins, fats, water, minerals, vitamins, emulsifiers, stabilizers antioxidants, and many others. It is the combination of these components which makes one food different from another. Also, each of these components is susceptible to a different form of deterioration, and the changes are subtle and complex. Realizing these facts, there are several deteriorative conditio
 

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Discussion Starter #12
More notes:

Food deterioration. The major causes of food deterioration are microorganisms, action of enzymes, chemical reactions, physical changes, time, and insects and/or rodents, multiple can be operating at the same time.

Microorganisms. Bacteria, molds, and yeasts.

Bacteria. Unicellular microorganisms of many forms. Some bacteria produce spores which are remarkably resistant to heat, chemicals, and other adverse conditions. Bacterial spores are far more resistant than yeast or mold spores, and more resistant to most processing conditions than natural food enzymes. All bacteria associated with foods are small, most are of the order of one to a few microns in cell length and somewhat smaller than this in diameter. (A micron is one-thousandth of a millimeter (0.001 mm) or about 0.00004 inch.) All bacteria can penetrate the smallest of openings, and many can pass through the natural pores of an egg shell once the natural bloom of the shell is worn or washed away.

Yeasts. Somewhat larger than bacteria, of the order of 20 microns in individual cell length and about half this size in diameter. Most yeasts are spherical or ellipsoidal in shape. Fresh vegetables, meat, poultry, and cheese often contain yeasts, but in these foods, bacteria outgrow the yeasts. When bacterial inhibitors are added, yeasts can dominate. Some yeasts are found in foods such as honey, molasses, sugar, and fruit. Salt-tolerant yeasts grow as films on brine food and on salted food and ham.

Molds. Larger than bacteria and yeast, they grow by a network of hair-like fibers called mycelia and send up fruiting bodies that produce mold spores referred to as conidia. The blackness of bread mold and the blue-colored veins of blue cheese are due to the conidia, while beneath the fruiting heads, the hair-like mycelia anchor the mold to the food. The mycelia are a micron or so in thickness and, like bacteria, can penetrate the smallest opening; or in the case of weakened skin or shell can digest the skin and make their own route of penetration.

Enzymes. Organic catalysts which are produced by the cells of animals, plants, or bacteria. Microorganisms possess enzymes which produce fermentation, rancidity, and putrefaction, likewise uninfected food plants and animals have their own enzyme complement. Unless these enzymes are inactivated by heat, chemicals, or other means, they continue to catalyze chemical reactions within foods. Some reactions to some levels are desirable, for example ripening of tomatoes after they are picked and natural tenderizing of beef on aging, but beyond an optimum point it becomes food deterioration.

Chemical. Examples include oxidation, color changes, reactions between a food container and its contents, and
the coagulation of proteins. A rule of chemistry states that for every 18ºF (10ºC) increase in temperature, the rate of a chemical reaction doubles. Applied to foods every such rise in temperature cuts food shelf life by half.

Physical changes. May cause food spoilage, or deteriorative changes such that the food is unsuitable to use. Examples:

Freezing. May cause destruction of emulsions and texture. Products such as salad dressing and mustard, contain a fat/oil and water mixture which does not combine without special processing or additives. When frozen the emulsion is destroyed and the fat and water separate. Fruits and vegetables will have their texture disrupted. Skins will crack, leaving the food susceptible to attack by microorganisms. The texture of canned fruits and vegetables becomes softened and mushy due.

Cold damage. Many fruits and vegetables as living systems have optimum temperature requirements. At common refrigeration temperatures of about 41ºF (5ºC), several fruits and vegetables are weakened or killed. Bananas, lemons, squash, and tomatoes are examples of products that should be held at temperatures no lower than 50ºF (10ºC) for maximum quality retention.

High Temperature. Most food should be stored between 50º-100ºF (10º-38ºC). Excessive heat can denature proteins, break emulsions, dry out foods by removing moisture, and destroy vitamins. Excessive heat in green vegetables causes cell walls and membranes to lose their integrity, acids and enzymes to be released, resulting in soft texture, off-colors and off-flavors. On muscle tissue proteins are denatured, proteins clump, and enzymes are inactivated, resulting in toughening texture, loss of waterholding capacity, cooked or caramel flavors, and development of off-colors.

Dehydration. Meat is 70 to 75 percent water. Fresh fruits and vegetables 80 to 95 percent water. When the humidity is too low in a storage area, dehydration results.

Excessive Moisture. Dried, dehydrated, and freeze-dried foods are very hygroscopic (readily taking up and retaining moisture) & if not properly packaged become lumpy or caked. A slight condensation on a food surface can become a pool for the multiplication of bacteria or the growth of mold. In a moisture-proof package, food materials such as fruits and vegetables can give off moisture from respiration and transpiration. This moisture is then trapped within the package and can support the growth of microorganisms.

Mechanical Damage. Damaged foods are more susceptible to invasion by microorganisms. Cell walls destroyed by mechanical abrasion liberates the inherent enzymes, these can begin deterioration.

Light. Can cause fading of color. Some vitamins are destroyed by light, notably riboflavin, vitamin A, and vitamin C. Milk in bottles exposed to the sun develops "sunlight" flavor due to light induced fat oxidation and changes in the protein. Sensitive foods can be protected by impervious packaging.

Potato warning. After exposure for two days or longer the skin and the flesh may develop chlorophyll and an alkaloid called solanine. The green tubers acquire a bitter, pungent taste. If eaten in quantity, they may be poisonous. Solanine is the bitter and poisonous component. Chlorophyll is tasteless and harmless.

Time. After slaughter, harvest, or manufacture there is a transitory period until the food succumbs to the above deterioration factors. The longer the time, the greater the destructive influences. Certain cheeses, sausages, wines, and other fermented foods are improved with aging up to a point, however, for the vast majority of foods, quality decreases with time, and the major goal of food handling and preservation practices is to capture and maintain freshness. Storage life is determined to a great extent by type of food, method of processing, method of packaging, and storage environment.

Insects & Rodents.

Insects are particularly destructive to cereal grains and to fruits and vegetables. When insects eat they damage the food and open it to bacteria, yeast, and mold infection. Insects are generally controlled in grain, dried fruits, and spices by fumigation with chemicals, the use of which may be prohibited in foods high in moisture because of the possible formation of toxic substances. Eggs may persist or be laid in the food after processing, as for example in flour.

Rodents. They not only consume but contaminate foods with urine and droppings may harbor several kinds of disease-causing bacteria. One rat pill, or fecal dropping, can contain several million bacteria. Even if the pill does not get into food directly, it will become dry and fall apart or be crushed. The particles then may be blown or carried into food.

Pest-proof the building. Deprive pests of food and shelter by following good housekeeping practices. Use appropriate control measures to exterminate pests.

Food is a very complex item composed of many substances, some of which are carbohydrates, proteins, fats, water, minerals, vitamins, emulsifiers, stabilizers antioxidants, and many others. It is the combination of these components which makes one food different from another. Also, each of these components is susceptible to a different form of deterioration, and the changes are subtle and complex. Realizing these facts, there are several deteriorative conditio
Excellent information. Thanks.

I started packaging dry goods in the trifecta of food-grade pails, mylar, and O2 absorbers. Mylar is the best oxygen barrier and protects wheat from moisture, the pail is like armor and the absorber removes oxygen. Removing the possibility of oxidation and killing all stages of bug life in 2 weeks, stopping any form of aerobic bacteria. The weak point seems to be the moisture content of grains going into the package. There doesn't seem to be an easy remedy to keeping moisture content at 10% or less other than purchasing wheat that is already there.

I looked into freezing. I quickly realized it's not an option for me.

Freezing seems like an antiquated method of killing bugs, it's ineffective and adds moisture to whatever you freeze which is a big "NO-NO" in oxygen-free storage.

Even the professionals don't agree on how to do it. I've seen freeze times from 3 days to 2 weeks per batch. Imagine packaging 400lb of grain per person for a year's supply, that's 1200 lbs for my household, in a stand-up freezer. How many pounds of wheat could get in the freezer doing a 1 freeze, it would take months to process. How would you keep moisture out of wheat waiting for a second freeze?

With the advent of Oxygen absorbers freezing doesn't seem like an option unless it's for very small amounts of food you're rotating through quickly. Something like a 5-pound bag of flour or something like that.

I'm storing wheat berries for long-term food storage and using store-bought flour for the short term. It's a lot of work but wheat berries have so many more uses: they can be sprouted indoors during the winter for a source of fresh greens, sprouted in a backpack as you move, cooked at camp, or hot soaked on the move, cooked whole like Ferro, ground to flour or (if still viable) planted in the garden for full-blown wheat or as a micro-green.
 

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Unless you have a flooded/wet basement or are using an outdoor root cellar, likely this won't be an issue.

Keep in mind if storing harvested items like potatoes, carrots, onions etc, you need some humidity This may dictate an indoor and outdoor storage schema.

Good luck.
 
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