How does sugar act as a preservative?

Jams and preserves are excellent at keeping bacteria at bay, so make sure you concentrate as to why.

18th November 2010
How does sugar act as a preservative? (iStock)

Asked by: ANON

Bacteria evolved in environments where the concentration of sugars and salts is the same as or lower than those inside the cell. High sugar concentrations cause the bacterium to lose water by osmosis and it doesn’t have any cellular machinery to pump it back in against the osmotic gradient. Without enough water, the bacteria can’t grow or divide. Mould is more tolerant though and can grow on some jams.

This question was part of The Great British Bake Off Q&A special, which appeared in the September 2015 issue of BBC Focus magazine. Read more of our Bake Off questions.


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