Reddit reviews Botulism (Deadly Diseases and Epidemics)

Food Canning
Part of the reason that the Poles have such a high botulism rate
is the fact that people often use a system of weck jars (weckglas)
to hermetically seal cooked food at home. Weck jars are glass
jars with rubber seals and a device used to create a vacuum.
The two major problems with this technique are inadequate
heating during the preparation of food and failure to follow
detailed instructions during wecking, which leave spores viable
and permits toxin formation. Destruction of spores requires a
temperature of boiling or above for at least 24 hours and the
wecking process does not accomplish this.

Boiling Water vs. Pressure Cooking
Two methods are used when doing home canning the boiling-
water-bath method and the pressure canner or pressure
cooker procedure. In both procedures, foods are heated in
containers to temperatures that should destroy the microorganisms
and their endospores, if any, that may otherwise
cause sickness or spoilage of the food. The method chosen
usually depends on the type of food that will be canned. The
boiling-water-bath method is normally used to can foods that
have a very low pH, otherwise known as high-acid foods such
as tomatoes, fruits, pickles, or sauerkraut. Table 8.1 uses the
terminology of high-acid and low-acid foods. A low-acid food
has a pH that is closer to 7, which is considered neutral. With
the boiling-water-bath method, jars of food are completely
covered with boiling water and heated for a specific period
of time. A rough guide is about 5 to 10 minutes for pickles;
10 minutes for jam; about 20 to 30 minutes for fruit, fruit pie
fillings, and applesauce; and 30 to 45 minutes or more for
tomatoes. (Begin timing after the water begins to boil.) The
time depends on the food, and the state or county extension
agencies can provide information about the time necessary to
heat each type of food.

When a pressure canner is used, the jars of food are heated
under pressure to temperatures in excess of 240°F (115.56°C).
This is a temperature above boiling and is necessary to destroy
the endospores of C. botulinum. Low-acid foods can be safely
canned using this method. Carrots are low-acid foods, so Mrs.
O’Riley should have used a pressure cooker to do her carrot
canning. Because she used a boiling-water canning method,
the spores survived, and when they germinated, they produced
their deadly toxins. As she found out, even a taste of food containing
these toxins can be potentially fatal.

The major factor that determines whether food will be
processed using a pressure cooker or the boiling-water bath is
the acidity of the food. Pickled foods and most fruits have a pH
that is acidic enough (below pH 4.6) to prevent the growth of
the vegetative cells of C. botulinum. In most of the cases of commercial
or residential canning that have led to botulism, the pH
of the materials involved was 5 or higher.

source: http://www.amazon.com/Botulism-Deadly-Diseases-Epidemics-Emmeluth/dp/1604132353