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As per the title, if for example butter preserves itself, and strawberry jam preserves itself, why does a blob of butter go mouldy if it’s dropped in the jam jar?
In: Chemistry
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Jam is preserved by the ridiculously high sugar content. Butter by the high fat content. A mix of the two has neither the high enough fat content or high enough sugar content to kill mould… and so problem.
In order for a food source to be preserved it has to be a toxic environment for bacteria/mould etc. too high a concentration of something may prevent growth but mixing two substances can dilute the toxic nature of the environment.
Imagine you have two rooms. One has a temperature of 110 degrees Fahrenheit. The other has a temperature of 30 degrees Fahrenheit.
If you are trapped in either room for an extended period of time, you will probably die. Stick them next to each other with a door in between so you can cool off or warm up depending on what you need in the moment, and you’ll last a lot longer. Open the door and let the two rooms mix, and you’ll get a nice, survivable room temperature.
Butter and jam are hostile environments to bacteria, but they are different kinds of hostile environments, and mixing them together compromises that hostility.
It is because the food itself is preserved not the container that holds the said food. For example, butter is not preserved when it is dropped into a jar that contains jam.