Microorganisms、too embarrassed to ask others about！（Part 7）

Microorganisms can be eaten.
Microorganisms are made up of proteins, fats, carbohydrates, and minerals, just like any other living organism. They are nutritionally superior and can be eaten. You all probably eat bread, yogurt, etc. Some of you may even like aged meats. Sometimes we take microorganisms as medicine. Dried yeast and lactic acid bacteria are sold as medicines.
In the 1960s and 1970s, there was a lot of research into the production of proteins from petroleum. The idea was to have microorganisms ingest/grow petroleum-derived hydrocarbons and use the bacteria as food or feed. Although this research seems to be in decline now, it may become active again in the future when food shortages are expected to occur. However, some microorganisms produce toxins, compounds that humans cannot digest, and extremely smelly substances. These are naturally inedible.

Canned food does not spoil.
Canned foods are heat-treated after sealing. As long as that treatment is complete, the product will not spoil. The shelf life of canned foods is usually two to three years. This does not mean that the canned food will go bad, but rather that the flavor will not deteriorate and the food will still taste good if it is still within the expiration date.
Canned foods were invented in 1810, but in the early days, the inside of canned foods sometimes spoiled due to poor sterilization. 1906 saw the enactment of the "Food and Drug Act" in the U.S., which regulated the distribution of altered products. Sterilization research has since progressed, and modern, safe canned foods are now available.
An exception is surströmming (canned salted herring), a canned food produced and consumed mainly in Sweden and famous as the "world's stinkiest food. It is manufactured in such a way that fermentation proceeds in the can without heat treatment.
(Note) Since there is no air in the can, i.e., anaerobic conditions, the growth of microorganisms in the can is anaerobic fermentation. In anaerobic fermentation, various organic acids, aldehydes, and gases are formed as fermentation products, which emit a strong odor. The author has never eaten surströmming, so I do not know exactly what it smells like, but I has worked with anaerobic bacteria in the past, so I can imagine it. Frankly, I don't want to imagine it.

Does dried food rot?
Dried food is a common preserved food. Does the term "preserved food" mean that it will not spoil?
Dried foods are preserved by evaporating water in the sun or wind to reduce the ratio of free water available to microorganisms (water activity) and by forming a film on the surface.
Microorganisms require a certain amount of moisture to grow. How much moisture is required depends on the type of microorganism. If dried food with zero moisture can be made, it will not rot. It is the same as an animal carcass mummified in the desert. Dried fish usually contains a certain amount of moisture, so it is best to think of it as "less perishable than raw fish.

Water activity
As salt or sugar is added to water, the vapor pressure gradually decreases. The ratio of the vapor pressure of such a solution to that of pure water is called water activity, and is usually expressed as Aw. For example, 1 mole of sucrose solution has an Aw of 0.9806, and 1 mole of salt solution has an Aw of 0.967.
Microorganisms have a specific Aw range in which they can grow, depending on their species. For most bacteria, an Aw between 0.997 and 0.980 is suitable. Saltophilic bacteria grow at an Aw of 0.75 to 0.85. Fungi grow at an Aw of up to 0.90. Fungi can grow up to around Aw = 0.90.
Jam is below Aw 0.80, so it can be said to be impervious to spoilage. Honey is said to be permanently impervious to spoilage. This is due to the fact that honey contains only 15-20% water and has an Aw of 0.5-0.6. Honey is indeed an extremely storable food, but if stored in a humid place, it can go rancid. Even at an Aw of 0.5, some types of bacteria can multiply, so it is impossible to say that honey will never go rancid.

Does water rot?
If it is pure H2O with no impurities at all, no microorganism can sustain life using only this, so we can say that it does not rot.
However, when it is placed in a glass and left to stand, carbon dioxide, nitrogen oxides, sulfides, and other substances in the air dissolve into the pure water and become nutrients. In addition, bacteria and mold spores in the air initially do not have enough nutrients, so they do not reproduce and die. Their carcasses become the base of organic matter and nutrients. In addition to fungi, there are other microscopic substances in the air, such as dust, which also fall into the water and become organic matter and nutrients.
Thus, over time, nutrients and organic matter base into the pure water from the air, thus turning it into water in which bacteria and other organisms can grow.