The roots of our food culture are deeply connected to preservation. In a not so distant past, we were taught the methods of preserving as we grew, a language and methodology learned as the seasons changed; this learning was gradual, incremental, natural. For the most part, we have abandoned the art of preservation, or, more fairly, are born ill-equipped with the necessary skills to practice it. In fact, we, as a society, have become fearful of preservation, most specifically due to the sinister Clostridium botulinum, the bacterium that causes botulism. This is a concern that is mostly tied to canning. My goal within this writing is to demystify some of the concerns around this method of preservation, as these findings have been instrumental in building my own confidence surrounding home canning.
I’d like to talk primarily about the spoilage enemies and how they can be defeated (keep in mind that these are specific to canning--some of these can actually be our allies in other methods of preservation, such as fermentation!)
The mechanisms for spoilage are as follows:
1. Microbial activity (bacteria, yeast, and mold)
2. Enzymatic activity, which leads to decomposition (i.e. pectinesterase, which breaks down pectin found in fruit cell walls)
3. Chemical activity (light + oxygen)
4. Mechanical damage (breaking, crushing, insect damage)
Microbes and enzymes are killed/deactivated by thermal processing via heating contents through submerging them in the water bath. Chemical activity and mechanical damage are combatted via hermetically sealed jars (i.e. mason jars, which seal contents in an oxygen-free environment). Bacteria are also eliminated by high acidity; this includes Clostridium botulinum, which is slightly more resistant to heating than other bacteria.
Peach preserves made on the mountain
I would like to dive further into two specifics of canning that have been on my mind recently: pH and sugar content. These are often seen as equal players in safety, but they actually affect the safety of canning to much different degrees!
Truly, the key concept to grasp for water bath canning is the difference between high and low acid foods. Acidity is measured by pH, and while 7 is a neutral pH (on a scale of 14), high acid foods are those with a pH of 4.6 or less and low acid foods have a pH higher than 4.6. I have attached below a link that includes the natural acidity of many common fruits, vegetables, and other foods. I find this to be a helpful tool in determining whether a food will need additional acid to be canned, or if it is even a good candidate for water bath canning (1). It is important to follow time-tested recipes because they have been determined to meet the acidity requirements!
That being said, if you’re anything like me and like to amend recipes to taste, it is of utmost importance to understand that changing recipes can alter the pH of the product as a whole. Consequently, changing recipes must be done with precaution, and ideally should be tested to ensure proper pH. Luckily, this can be done with the help of a pH meter! In fact, it must be done for all commercially sold canned goods (even for small operations). Meters can be a bit pricey, but potentially viable in my mind considering the money you could save by preserving food rather than buying it at the store. Good resources for pH meters and strips (and other considerations regarding pH) are listed below (2,3).
Interestingly, sugar (and salt) are unnecessary when it comes to home canning (4-6)! This was an incredible finding for me. I often find certain recipes to be far too sweet for my taste and was hesitant to alter the content for fear of food safety. Importantly, there should be a distinction set between food safety and preservation of the food "appeal," which includes texture, color, taste, appearance. In this way, sugar has texture and color-preserving properties, but not food-safety preserving properties. This could also be a relevant piece of information for persons who are avoiding sugar and salt for health reasons. I encourage interested parties to check out the resources I have included at the end of this blog if you are interested in reducing either of these, but it truly seems that these two ingredients can pretty much always be adjusted to taste.
Pasta sauce made from tomatoes from AMI’s Urban Farm, ready to canned.
I hope that this information is as useful to you as it has been to me in researching it. Canning is an excellent way to save the season and it shouldn’t be onerous or filled with fear! My hope is that you may be able to gain confidence in canning through these sources as I have if you haven’t grown up with it, or even if you are just looking to try some recipes that you have never tried before. Cheers!
Sources and Resources:
Here are more in-depth sources regarding available water content, for those that may be concerned about reducing sugar or salt:
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