This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
You know, I think someone could make a mint by inventing the "home botulism
test kit" that would work in the same way that a home pregnancy test kit
does. But we don't, so...
Remember, that despite the bacterium's fearsome reputation, _C. botulinum_
is still a microbe, and can be killed using a little basic microbiology.
Preserving recipes utilize at least one of these 5 microbiological facts,
good recipes often use several.
1. _C. botulinum_ bacterium dies at 212 F/ 100 C.
2. _C. botulinum_ spores die at 240 F/ 116 C.
3. Botulism toxin denatures at 185 F/ 85 C.
**(All temperatures must be maintained for least 15 minutes, and
the heat must be consistent throughout the food, fluid, and jar.)**
4. _C. botulinum_ spores cannot hatch in strong acid solutions
of pH 4.6 or below. (Some sources claim pH 4.7.)
5. _C. botulinum_ cannot grow, develop, or multiply in food
with a water content of less than 35%. (Food dehydrators have another
set of toxic pests to worry about, see IV.6 about aflatoxin.)
Common sense is a first step in the prevention of botulism.
1.) _C. botulinum_ bacteria and spores usually live in soil.
Thus clean foods of soil, dust, grit, etc, using fresh, cold water. Change
wash water often. Don't can "drops", fruit that has dropped to the ground.
Pay special attention to cleaning root crops (including garlic!), shucking
skins or peeling that produce if need be.
2.) One variety of _C. botulinum_ (E) lives in flat water. So, you want to
make your brines, etc, with fresh cold water. Start with fresh, cold water
if you are boiling to sterilize, or perform other operations.
3.) Botulism spores remain dormant under high acid conditions. Fruit is
quite high in acid but also contains a lot of sugar, so the fruit still
tastes sweet. Vinegar is added to vegetables to pickle them. You can can
foods like this in a boiling waterbath. However, the concentration of acid
(ionic strength) is also very important, so you want to use vinegars of a
known strength (5% or 5 grain); add the recommended amount of vinegar, citric
acid, or ascorbic acid described in your recipe; can just-ripe fruits. For
safety's sake, you shouldn't cut down the amount of vinegar in a recipe, take
a cue from fruit and add a little bit of sugar to cut down the extreme acid
taste. Vegetable pickles should be immersed in the vinegar or brine. *BTW,
finding out that honey is a source of botulism spores (infant botulism),
means that I'm not thrilled about the idea of substituting honey for sugar,
as the Rodale Institute appears to be.*
4.) Botulism spores, bacterium, and the toxin are killed by high heat.
However, all the contents of the jar has to get to the target temperature,
no matter the volume, and the temperature should be sustained for about 15
minutes. Follow recipes exactly, including jar sizes and treatment of the
jars. Process at least for the times indicated, but remember that you have
to increase processing time or pressures depending on your altitude. (Water
boils at lower temperatures the higher your altitude.) Note that larger
size jars usually require longer processing time, because the heat has to
penetrate through the jar.
Acid and heat are each used in canning things that are borderline acid, such
as tomatoes, tomato vegetable mixes (like salsa and spaghetti sauce),
vegetable relishes, and other vegetable mixes. The idea here is that you
can't increase one thing to avoid other procedures. (You can't increase acid
to avoid pressure canning).
5.) Botulism cannot grow or develop without water.
In making jams or jellies, enough sugar and pectin is added to form a gel,
depressing the amount of free water available for bacteria to grow. This
is one of the reasons why special care has to be taken if the jam or jelly
is extremely runny.
Foods preserved in oil (raw garlic, chilis, dried tomatoes) create a special
case. Oil contains no water, as it is centrifuged out during processing.
If an item is dependably dry, under 35% water content, adding it to the oil
should not cause problems, as long as your items are well immersed (1 inch
of oil covering). Dry herbs, seeds and spices, dried chiles, even sundried
tomatoes should not cause problems. (N.B: Research from the Australian
Extension Service--sundried tomatoes are more acid than hydrated ones: pH
4.0 for dried, 4.6 for hydrated--LEB). However, the dehydrated food must be
properly dried, conditioned, and not case hardened (case hardened things are
hard and crunchy on the outside, soft and gooey on the inside). The jury is
out on wet herbs.
If you try to preserve a lot of "wet" items in oil (garlic cloves, chopped
onions, ginger root, fresh chiles), you might have a heap of trouble. Oil
doesn't contain much dissolved oxygen, so it is a good anaerobic medium.
Raw garlic, onions, ginger are all rootcrops, and each contain over 35%
water. Chilies often are added to oil in a non-dried state. Generally, you
want to "pickle", or at least allow your wet, raw item to take up some 5%
vinegar for about 15-20 minutes before putting into the oil. Chunky items
(i.e. garlic cloves) should be smashed, crushed, or chopped to get the
vinegar into the item.
Simple, but through, sauteing of your chosen flavoring in your oil can also
get rid of spores, since they evaporate free water, and the oil can be heated
to above 240 F. Yet another idea is to refrigerate your flavored oils, as
bacterial growth is very slow below 40 F/4 C.
In addition, the garlic-in-oil botulism problem began when garlic pastes in
olive oil were introduced in grocery stores. Many of the botulism
poisonings occurred when these pastes were used in cold pasta, salads, and
salad dressings. If you are going to be using your flavored oil for sauteing,
stir fry, or deep fat frying you will easily heat your oil to above any of
the target temperatures described above.
Since the toxin is denatured at 185 F/85 C, if you are concerned about a
canned good the usual procedure is as described in the above section (to
hard boil the contents for 15 minutes). NOTE: This will denature the
botulism toxin. Other toxins, such as those caused by _Staphococcus_, will
not denature until temps of 240 F/116 C are reached and sustained for 30
minutes. As a matter of fact, a hard boil in that case will break open the
bacteria, and more toxin would be released into the food.