Chapter 4 – Spoilage, Insects and Molds


Insect infestations can occur in a wide variety of foodstuffs such as flours, meals, pastas, dried fruits or vegetables, nuts, sweets, whole grains, beans, sugars, TVP, jerky, bird seed and pet foods.

Naturally, the best way to deal with an insect infestation is not to have one in the first place.  Try to purchase your goods from suppliers who are clean and who turn over their inventory quickly so the products you purchase will be less likely to have bugs.

When you buy foodstuffs examine them closely to be sure they are insect free.  Check for any packaging or use by dates to insure their freshness.  Don’t shake the package, most adult insects will be found in the top couple of inches of the product and shaking the package will mix them into the contents disguising their appearance.  If the package does turn out to be infested, return it for replacement.

If not already packaged for storage when you buy them transfer your foods into air- and moisture-tight containers so they cannot be invaded after you have brought them home.   With sufficient time, some adult and larval insect forms can penetrate paper, cardboard and thin plastic packaging.  Storage containers should be glass, metal, or heavy plastic with tight fitting lids.  As with everything in food storage, you should use older packages before newer ones and opened packages before unopened ones.

Storage areas should be kept clean.  Don’t allow grain, flour, beans, bits of pasta or other food particles to accumulate on shelves or floors.  Cracks and crevices should be sealed or otherwise blocked. Except for sticky spills, vacuuming is the best method of cleaning as soap and water can wash food particles into cracks.

Insects may also get their start in chairs, sofas and carpets where food is dropped and not cleaned up.  Don’t forget to replace the filter bag on the vacuum as some insects can survive and reproduce in the bag.

Bags of dry pet food and bird seed can harbor insect infestation.  Decorative foodstuffs such as ears of colorful Indian corn, colored beans and hard squashes can carry insects that may infest your edible food.  Even poison baits can harbor flour beetles.


Should you find that in spite of buying fresh products and using careful packaging techniques you have an insect infestation, you can try some of the following steps:

1. If the food is too heavily infested to try to save it should be disposed of as soon as possible.  Remove from the kitchen or food storage area immediately so as to not infest other foods.

2. Large bugs can be sifted or winnowed out if the food’s not too heavily infested and you want to try to save it.  Then treat by placing into a deep freezer at 0º F (-18º C) for three to seven days depending upon the size of the package.  Refrigerator freezers usually do not freeze low enough to effectively kill all of the life stages of insects, but if left there, will slow their development.  If freezing is not workable then the product could be spread on baking sheets and heated to 150º F for fifteen to twenty minutes,  cooled and repackaged.  This will shorten shelf life so heat treated foods should be consumed shortly thereafter.

3. The surface areas where the food containers are stored can be treated with an insecticide.  This is not a replacement for clean storage habits and good containers, but is rather a supplement. This will not control insect infestations already in your stored foods.

Spray the shelf surface with 0.5% chlorpyrifos (Dursban), 1% propoxur (Baygon), 0.5 percent diazinon, or 0.25 percent resmethrin. You can find any of these in the hardware store in ready to apply packages.  If a sprayer isn’t feasible then they can be applied with a paint brush.  Allow the solution to dry thoroughly.  Cover the shelves with clean, untreated shelf paper then put properly packaged foods back on shelves.  READ THE PRODUCT LABEL FOR SAFETY INFORMATION CONCERNING CHILDREN AND PETS.

Household bleach, Lysol and other sterilizers will not control insect infestation, though they can be used for mold, mildew and algae.

You may continue to find some insects after the cleanup is finished.  This could be for several reasons.  It may be they escaped from the packages they were infesting and did not get cleaned up.  There may be more packages infested than were originally found or, there may be hiding places in the storage area that need attention. Once you have carefully eliminated all food sources, the bugs should disappear in a few weeks.


Molds are fungi like mushrooms and yeast.  Also like mushrooms, they reproduce by releasing spores into the air that land on everything, including your food and food storage containers.  If those spores begin to grow, they create thin threads that spread through their growing medium.  These threads are the roots of the mold fungus, called mycelium.  The stalk of a mold fungus is the portion above or on the surface of the food.  It produces the spores and gives the mold its color.  We’ve all seen examples of this when we discover a dish of something or other left too long in the refrigerator only to become covered in a mold fuzz.

Molds can grow anywhere they have a growing medium (their food), sufficient moisture and warmth.  Some can even grow at refrigerator temperatures, albeit more slowly than they would if it were warmer.  These fungi can also withstand more salt and sugar than bacteria, which is why you sometimes find mold in jellies and jams with their high sugar content and on dry cured products like ham or bacon with their high salt content.

In the past, a slight amount of mold was commonly felt to be harmless and the food consumed anyway.  For molds that were intentionally introduced, such as the mold in bleu cheese, this is fine.  For the unintentional molds, it could possibly be a serious error in judgment.  These unwanted molds could be producing toxic substances called mycotoxins which can be very bad indeed. Mycotoxins are produced around the root or mycelium of molds and these mold roots can penetrate deeply into the food.  Mycotoxins can survive for a long time and most are not destroyed by cooking.  The molds probably best known for this dangerous spoilage are the various Aspergillus species which produces a mycotoxin known as aflatoxin, but there are other dangerous fungi as well, such as the Fusarium molds. Both of the above affect grains and some legumes.  See B.3 Molds In Grains and Legumes.

IMPORTANT NOTE: In wet pack foods such as your home canned goodies, molds can do something else as well, possibly with lethal consequences.  If they find their way into wet pack acid foods canned by the boiling water bath method, whether by reasons of improper procedure or contamination after the fact, they can consume the natural acids present in the food. The effect of this is to raise the pH of the food in the container, perhaps to the point that it becomes possible for spores of Clostridium botulinum, better known as botulism, to become active and reproduce.    For this reason, moldy wet pack foods should be safely discarded.  This most deadly kind of food poisoning has an entry of its own in the bacterial spoilage section.

Molds in low acid foods canned by the pressure canning method are equally dangerous and should also be discarded in a safe manner.


You can do a number of things to minimize unwanted mold growth in your kitchen, food storage areas and refrigerators.  If your kitchen is at all like mine, it is the refrigerator that is going to collect the most fungal growth.  This can be dealt with by washing the inside every couple of months with a tablespoon of baking soda dissolved in a quart of warm water.  Rinse clean and allow to dry.  The black mildew that grows on the rubber door gaskets and other places can be dealt with by wiping down with a solution of three tablespoons of household bleach in a quart of water.  I generally use a soft bristle brush for this.  A really bad case will not bleach back to a white color, at least it won’t for me, but will instead turn pink or red after the bleach has carried out its disinfection mission.

The rest of the kitchen can be kept mold free by keeping the area clean, dry, and spraying occasionally with a product such as Lysol. Patches of mold can be eliminated with the bleach solution used on the refrigerator doors.

Try not to purchase more fresh food than you’ll be able to eat in a short period of time.  This will keep you from having to deal with the moldy remains that didn’t get eaten.   If food does go moldy, don’t sniff it.  This is a good way to give yourself respiratory difficulties if you are at all susceptible to mold allergies.  Moldy food should be disposed in such a manner that your animals and children won’t be able to get into it. Mycotoxins are every bit as bad for your animals as they are for you.

Obviously, you don’t have to throw out everything that shows a spot of mold on it.  Some foods can be safely dealt with and still partially saved if they show signs of fungal growth.  Below is a set of guideline from M. Susan Brewer, Ph.D., R.D., a specialist in food safety.  Her articles and works are found in many state university extension services publications lists.

If the food shows even a tiny mold spot, follow these guidelines:

1. Hard or firm foods with tiny mold spots can be trimmed; cut away the area around the mold (at least an inch) and rewrap in clean wrap.  Make sure that knife does not touch the mold.

Hard Cheese (Cheddar, Swiss, etc.)
Bell Peppers, Carrots, Cabbage
Broccoli, Cauliflower, Brussels Sprouts
Garlic, Onions
Potatoes, Turnips
Apples, Pears

2. Soft foods such as cheese slices, cream cheese, sour cream and yogurt should be thrown away.

Soft Cheeses, (Mozzarella, Brie, etc.)
Sour Cream, Yogurt, Cottage cheese
Bacon, Hot dogs, Sliced lunch meats
Meat pies
Opened canned ham
Most left-over food
Bread, Cakes, rolls, flour, pastry
Peanut butter
Juices, berries
Jam, Jellies, Syrups
Cucumbers, Tomatoes
Spinach, Lettuce, other leafy vegetables
Bananas, Peaches, Melons
Stored nuts, whole grains, rice

If good equipment and proper technique are used, it is unlikely you will ever have mold growth in your unopened canned goods. If you do have such, there was either a flaw in the procedure used, or something affected the jar or can after the fact to break its seal.  In any event, once the food has molded, it is past saving and should be discarded in such a way that children and animals will not be able to get into it.  The most likely home canned products to show mold growth are jams and jellies sealed with paraffin wax.

There are a number of points in the canning process where this can occur:

(1)  In the time after the jar is taken out of its boiling water bath, but before it is filled.

(2)  In the time between when the jar is filled and covered with the melted wax.

(3)  When the wax cools, if it pulls away from the side of the jar, leaving an opening for the mold to get in.

(4)  If bubbles form in the paraffin, which break and leave holes.

For these reasons most canning authorities no longer recommend using this technique.  If you must do so, the jars should be boiled for at least 10 minutes before the jelly is poured.  The filled and wax capped jars should then be covered with some sort of protective lid.  The book, Putting Food By has excellent instructions on this or see the applicable section of the FAQ.


It has long been known that eating moldy grain is bad for your health with the ugly consequences of eating ergot-infected rye being a well known example.  It has only been about thirty years, though, that intensive study has been carried out on other species of grain fungi and their respective mycotoxins. Fortunately, for those of us in the U.S., the USDA and the various state departments of agriculture go to a great deal of trouble to detect grain and legumes infected with these toxic fungi.  In some of the less developed countries, the citizenry are not so lucky.  It is good to have something of an understanding of what one should do to prevent mold growth in ones stored grains and to have an idea of what to look for and ask about when purchasing grains and legumes.

The one fungal group that has caused the most commotion in recent history are the various Aspergillus species of molds.  Under certain conditions with certain grains, legumes, and to a lesser extent, nuts, they can produce a mycotoxin called aflatoxin.  This is a serious problem in some parts of the world, most especially in peanuts, occasionally in corn.  I am not aware of any documented deaths in the United States from aflatoxicity, but other nations have not been so fortunate.  What makes aflatoxin worrisome in this country is that it is also a potent carcinogen (cancer causing agent).

In addition to the Aspergillus molds, there is also a large family of molds known as Fusarium which can produce mycotoxins of their own, none of which do you want to be eating directly or feeding to your food animals where you will get the toxins back indirectly when the animal is slaughtered and eaten.

The Federal and state governments continuously monitor food and forage crops entering the marketplace.  Those products found to be contaminated with mold or mycotoxins are not allowed to be sold for food.  Once purchased however, the responsibility is yours to keep your food safe from mold growth.  If you have already found mold growth in your whole grains, meals, flours or other grain products, they should be discarded. Most mycotoxins are not broken down or destroyed by cooking temperatures and there is no safe way to salvage grain that has molded.


The easiest method to prevent mold growth in your stored grains and legumes is to keep them too dry for mold to grow.  The Aspergillus and Fusarium molds require moisture contents of 18% and above to reproduce.  This is subject to some variability, but in all grains and soybeans, they must have a moisture content of that level. If you are storing raw (not roasted) peanuts, in the shell or shelled, you want to get the moisture content to less than 8% as peanuts are particularly susceptible to mold growth.  The recommended moisture content for all other grain and legume storage is no more than 10%.  Please see part 2.A.3.1 Grains and Legumes for a method to determine moisture content.  At 10% moisture, there is simply too little water for fungi to grow.


Like the fungi, bacteria are everywhere, in the water, soil, air, on you, your food and your food storage containers. Fortunately, the vast majority of the bacteria we encounter are relatively harmless or even benign and only a few represent a danger to us and our stored foods.

Bacteria can be much more difficult to kill than molds and insects.  Some are capable of continued growth at temperatures that would kill other spoilage organisms.  When conditions are such that they are unable to grow, some bacteria can go dormant and form spores. These spores can be quite hardy, even to the point of surviving boiling water temperatures.

In order to grow, bacteria must have water, some species needing as little as a 20% moisture.  For properly packaged dry grains, legumes, powdered milk and other low moisture foodstuffs bacterial spoilage will never be a problem as their moisture levels should be too scant to support growth.

WARNING: It is in wet pack canned goods (where the container has free liquid in it) and fresh foods we must be the most concerned about spoilage bacteria.  It is here that a little bad luck and a moment’s inattention to what you are doing could kill or seriously injure you or some other person who eats the foods you’ve put by.  In both home-canned and commercially-canned goods, IF THE CAN IS BULGING, LEAKING, SMELLS BAD, OR SPEWS LIQUID WHEN YOU OPEN IT THEN THROW IT OUT! But, throw it out safely so that children and animals cannot get into it.


Clostridium botulinum is one of the oldest life forms on this planet dating from a time before the Earth had an abundant oxygen atmosphere.  Like the gangrene bacteria, it is an anaerobic organism meaning it lives and grows only in the absence of free oxygen.  When conditions are not suitable for growth the bacteria can form durable seed like spores which are commonly found in the soil.  This means that C. botulinum can be brought into your life on raw produce, tools, hands or anything else that came into contact with dirt.  To further complicate matters, botulinum spores are extremely heat-hardy. The bacteria itself can be killed by a short exposure to boiling water (212º F AT SEA LEVEL PRESSURE), but its spores can not.  To kill them, the food product and container must be exposed to temperatures of 240º F (AGAIN AT  SEA LEVEL PRESSURE) for a long enough period of time to allow all of the food in each container to come completely up to the proper temperature. Only a pressure-canner can reach the necessary temperature.

It’s not the bacteria or its spores which are directly deadly, but the toxin the bacteria creates when it grows and reproduces.  In its pure form, botulism toxin is so potent that a mere teaspoon would be enough to provide a fatal dose to hundreds of thousands of people. It is this lethality that is why every responsible book on home canning, food preservation, and food storage hammers constantly on the need for care in technique and method and why spoilage must be taken seriously.

Like any other life form Clostridium botulinum must have suitable conditions for its growth to become a danger.  One of the most important of these is water – the botulism bacterium needs moisture in the 35% range to grow making it a danger only in improperly processed high moisture foods.   Another requirement is suitable pH, which is the measure of acidity or alkalinity in a substance and is measured on a scale of 1-14.  Anything above 7 is considered alkaline and everything below 7 is considered acid.   If the acidity of your wet pack food is BELOW pH4.6  then C. botulinum is unable to grow.  Keep in mind that in foods pH is not necessarily stable and could possibly change if other spoilers like mold are able to grow.  If the product should change to a lesser acidity than pH4.6 your previously botulinum proof food may start allowing the lethal spoiler to grow (see B.2, molds in canned goods).  This is why it is vital to use proper technique, even for acid foods like tomatoes.   It has been found that when this pH shift occurs allowing C. botulinum to become active producing its lethal toxin the bacterium also produces minute amounts of acid which can lower the pH of the poisoned food back into what should have been the safe zone had the pH not jumped up and allowed the bacteria to grow.  Again and again — use good technique and pay attention to what you are doing.

Unlike fungal mycotoxins Botulinum toxin can be destroyed by boiling food briskly in an open vessel for fifteen minutes.  Because of this, if your canned food shows any safety problems you should follow this procedure.  If the food shows even the slightest mold growth, keep in mind that mycotoxins are not for the most part broken down by heat and dispose of the food safely.

I won’t go into the hows of home canning here. For that I strongly recommend that you read the FAQ, the Ball Blue Book or most especially the book Putting Food By for in depth information on this subject.


Every living organism uses enzymes of many sorts in its bodily functions as part of its normal life cycle.  Enzymes are used in creating life.  After death, enzymes play a role in the decomposition of once living tissue.  The enzymes in a tomato help it to ripen and enzymes produced by the tomato and whatever fungal and bacterial spoilers are on it cause it to decay.

Fortunately, slowing down or stopping the action of a food’s enzymes is much easier than slowing or stopping some of the bacterial spoilers mentioned above.  Enzymes are most active in a temperature range between 85-120º F and begin to be destroyed when the temperature goes above 140º F.  Cold also slows down the action of enzymes, which is why fresh tomatoes last longer in the refrigerator than they do on the kitchen table.  Most enzymatic action also requires moisture to occur.  In foods stored at 10% moisture or less, there is not enough moisture for most enzymes to be active.