Food spoilage is one thing everyone of us has experienced firsthand. Put a food outside and watch it get spoil in front of you as molds and bacteria begin to deal with the food. Food spoilage is a fact and the only way we have learned to keep our food from spoiling is to cheat and outsmart nature.
Before refrigeration, people have been preserving food one way or the other by sun drying, fermenting, and salting and they were able to slow down the process of spoiling. Today we have had more methods of preservation including freezing but one method that is now common with food preservation is canning. It looks like everything that needs to stay long only needs to meet canning process and its shelf life will increase but what is the science behind this method.
Canning is simply building an impenetrable fortress around food so as to prevent the entry and exit of anything at all. This process has over the years been perfected to ensure that food items stay in sterilized cans and closed in an airtight manner so there will be no entry or escape of air after which the cans are placed into boiling water or steam to ensure any bacteria or microbe is killed and so neutralizing early spoilage.
Canning creates a hostile environment for microbes which are responsible for food spoilage and it also prevents new microbes from reaching the food thereby keeping the food safe. Canning might be the most common method now but it isn't the only method and the old methods I mentioned in the past does a great job as well. For instance, drying is great way to preserve food as it increase the shelve life of the food for hours or days compared to when it isn't dried. With drying, the moisture is removed making it difficult for microbes to effectively thrive in the food.
We also used fermentation which is the use of bacteria to produce lactic acid which serves as a preservative to keep food safe. Also freezing is another technique that has been for a while now while we dry out water in some food in drying, we freeze other types of food to help them stay longer.
Back to canned food, while it is safe, there is a concern with it and it is botulism caused by a toxin released by Clostridium botulinum which thrives in environment with low oxygen and this is common with improperly canned foods or foods that were not heated properly for the right period of time. If you think you are going to see or identify the toxin in improperly canned foods, then you are joking because it is colorless, tasteless and odorless and consuming small amount can lead to severe illness and death.
I remember a time I bought a can of sardine and I saw it had oil around it and this was because it had a little opening that wasn't noticeable if cleaned. The woman tried to convince me to purchase it but I insisted that I wasn't going to purchase it as it was me taking a risk with my life and so should everyone do because consuming a canned food that has already been opened, has a bulge, leak or rust can be harmful to ones health as it might have been contaminated or spoiled.
One rule I have learned is when in doubt, throw it out because it is better to be safe than sorry. The future of food preservation goes beyond canning as researchers are doing a lot of experiments to get better ways of preserving food but for now, canned food still remains a staple but when purchasing, check properly for any sign that throws you off and leave it immediately.
You Can Study More
https://pmc.ncbi.nlm.nih.gov/articles/PMC4517017/
https://www.sciencedirect.com/topics/food-science/canned-food
https://www.cdc.gov/botulism/prevention/home-canned-foods.html
https://www.nal.usda.gov/exhibits/ipd/canning/exhibits/show/results/botulism
https://www.who.int/news-room/fact-sheets/detail/botulism