More specifically, does almost boiling water have the same effect? Or is there something particularly special about boiling water that kills germs/bacteria? – if so what is it, and why is it special?
In: Chemistry
The increased temps denatures (ruins the function of) proteins. Like egg whites (high in protein) losing its elasticity and hardening when you cook them.
It’s just the temperature. You don’t need to boil it necessarily, usually just keeping it above 160°F for long enough will kill most bacteria, but boiling water for a little while is usually faster and you can tell when water is boiling by just looking at it and leaving your stove on, whereas you’d need a thermometer and/or some fancy tech like a Sous vide to keep it at around 160° or any other specific temperature.
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heat can cause proteins (the things that allow all living things to function) to denature. Proteins rely on having a certain shape to function and when they denature, they loose that shape (this is the same thing that happens when we cook food).
As for can this happen at lower temperatures, kinda. This happens in food all the time (chicken is safe to eat at 165, well below boiling). pasteurization can be done below boiling point as well. But it depends on the bacteria, and it depends on the proteins that you need to destroy. Another thing to keep in mind is that for pasteurization, the hotter the temp, the faster you can do it. So while it’s possible to do it at lower temperatures, it takes longer. Another thing to keep in mind is that boiling is readily identifiable, you don’t need a thermometer to identify the temp.
High temperatures disrupt their enzymes, rendering them incapable of carrying out their cellular functions. Even higher temperatures cause their plasma membrane to burst open, causing the death of the bacterial cells.
Edit: At lower temperatures, their enzymes also get disrupted and crystallisation of their cytoplasm also causes cell death, however, they may have enough time to form spores, toxins, etc. which also get disrupted at high temperatures. So, boiling or UV radiation is generally preferred.
It isn’t that the water *has* to be boiling to kill bacteria; according to the World Health Organization, 70 degrees celsius is actually enough to kill most pathogens (viruses, bacteria, etc.) given a pretty short amount of time (less than a matter of minutes). This is because the bacteria just can’t handle that high of a temperature.
But if you’re out in the woods and need to purify some water, you might not have a thermometer and you probably don’t want to risk getting a stomach virus. So boiling the water is a very simple way of making sure it has reached a temperature high enough to kill the bacteria (even though they probably died long before it started boiling).
Heat is really just stuff jiggling around. Hotter things jiggle more. Getting the bacteria really hot literally tears them up from all the jiggling.
Very simply, boiling water kills almost anything. Most organisms simply can’t survive in hostile environments. Boiling water is a hostile environment.
Don’t believe me? Dip your hand in 100c (212f) water for a couple of minutes and you’ll be able to peel your skin off.
Generally, the heat changes molecules in the bacteria and this is what kills them. Most bacteria are killed by boiling, but some create endospores. These are like armored heat resistant escape pods for the germs, and boiling water won’t kill them in a reasonable time. The endospores will just hatch and grow a new colony of bacteria when things cool off. Botulism bacteria are an example of these germs. Therefore, canned goods that aren’t acidic (not tart or sour) have to be pressure canned since that uses higher temperatures to kill the endospores.
Some germs are killed at lower than boiling temps, say 160 F, most are killed by boiling, and others take higher temps.
Many of the proteins in any living creature are held in their shape by a type of weak bond called a Hydrogen bond. What makes a protein work is its shape.
Now, you may or not be aware, but what your DNA does is have the codes for proteins. Everything that makes you you is either directly proteins or is controlled by proteins. And if they can’t do there thing… life doesn’t work.
It’s the same for bacteria. If you get them hot enough they start to break down and life stops.
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