The Logic Behind an Era of Safe Canning

Canned food is something that most everyone is familiar with. From canned sardines to peaches to condensed milk, canning food is a useful preservation method for our favorite foods. Better food preservation in turn means that the foods we love are available year round. Iconically, the ridged metal can comes to mind, but there are other forms of canning that involve glass jars with metal lids used primarily for home canning but also seen sometimes in stores.

Fig. 1: A sample of canning styles (Best in Packaging)

Many families can their own excess garden goods at home to eat later; according to the CDC, 1 in 5 American households participate in home canning [1]. There are two main sterilization methods used in home canning, one involving boiling the cans and the other involving high temperatures as well as high pressure [2]. Heat kills bacteria, mold and other bad stuff for reasons previously discussed in Party Science, Part 3: The Tasty Grub. However, for the same reason that bacteria are killed by heat the flavor of the preserved food may be affected as well. Pressure kills bacteria possibly as an effect of the expansion of dissolve gases within bacterial cells [3]. Acidity is another factor that affects bacterial survival, and it has been found that acidic foods inhibit the growth of pathogenic bacteria enough to permit the use of High Pressure Processing (HPP) as the only additional sterilization technique while basic foods such as meats require heat treatment as well [4]. 

In our current era when canning is considered a generally understood science, it is uncommon to hear of botulism cases from canned foods, especially those produced commercially. Botulism is the name of an illness caused by Clostridium botulinum bacteria that generate botulinum toxin. There are eight different forms of botulinum toxin labeled types A through G (botulinum toxin C is divided into C1 and C2), of which type A is the most potent and types A, B and E are associated with human botulism. Botulinum toxin is one of the most poisonous known biological substances and also happens to be the active ingredient in Botox injections. Botulinum toxin binds to receptors on the presynaptic surface of neurons and is accepted into the neuron where it interacts with proteins related to acetylcholine vesicle transport to prevent the neurotransmitter’s release [5].

Fig. 2: Botulinum toxin mechanism of action (Student Pulse)

Symptoms of botulism are typically those related to an impaired nervous system, such as blurred vision, muscle weakness, slurred speech, drooping eyelids and difficulty swallowing. The presentation of these symptoms after possible botulism exposure is an emergency situation as antitoxins exist to treat botulism if administered promptly and progressed botulism may be fatal due to respiratory system paralysis [6]. 

But botulism and other canning-related illness cases today are rare and for the most part, the effects of canning have been positive for human survival during harsh times and the winter season. I for one love having corn, my favorite vegetable/grain thing, available all year round, and for that I am thankful we have this technology. How about you? Let me know what you think in the comments below, and check out this link to an instructional video if you are interested in canning your own foods at home.