Living · 6 pages · 12 min
How sugar keeps a jam
A high concentration of sugar ties up the water microbes would use.
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From the opening
Sugar keeps a jam when its concentration is high enough to lower water activity, tying up water that bacteria, yeasts, and molds would use. The sweet taste is the solute itself; the keeping is the scarcity of free water. The opening covers high sugar lowers water activity, ordinary sweetness does not preserve, and a wet surface can dilute the jam.
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Inside
- High sugar lowers water activity
- Ordinary sweetness does not preserve
- A wet surface can dilute the jam
- Honey and salt use the same idea
- Where the idea stops applying
- A distinction worth keeping
Sources
- Water activity in high-sugar preserves
- Osmotic limits on microbes in concentrated syrups