How can sugar act like a food preservative when it’s said to attract bacteria?
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In things like jams and such, a lot of water is removed and sugar added. Because there’s much less water in jam than in a bacterial cell, and the concentration of sugar is high, water inside the cell rushes out – which tends to kill or at least disable many pathogens.
You need very, very, very high concentrations of sugar.
And it works due to osmosis.
Osmosis is a process where water is naturally draw from areas of high concentration to low concentration.
So if you put bacteria, a little cell full of water it needs, into a very high sugar concentration like honey, all that sugar actually pulls the water out of the bacteria, killing it.
If you have a little bit of sugar, it can be eaten by bacteria. If you have a lot of sugar, at high concentrations, then the bacteria can’t actually eat it before the sugar “eats” the bacteria. The water in the bacteria will get drawn out of it and into the sugar (this is why sugar will form clumps in moist environments). This kills the bacteria, just like dehydration kills us.
Sugar is hygroscopic which means it absorbs moisture from the atmosphere it is exposed to. If it is concentrated high enough (like jams and honey) then it sucks the moisture out of bacteria effectively destroying them.
Most preservation works by withholding water — which is needed by all living things, including bacteria.
Hence jams, pickling, salting or just straight-up drying.
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