Salt and sugar preserve foods primarily by creating a hypertonic environment, which inhibits the growth of microorganisms.
Creating a hypertonic environment means increasing the concentration of solutes (salt or sugar) outside the microbial cells and within the food itself. This high concentration difference causes water to move out of the cells through a process called osmosis, from an area of lower solute concentration (inside the cell) to an area of higher solute concentration (outside the cell).
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Salts are able to draw water out of the food and dehydrate it. This extraction of water from the food is a direct consequence of the hypertonic environment created by salt. Sugar works in a similar way, also drawing out moisture.
The Mechanism of Preservation
The hypertonic environment leads to food preservation through the following steps:
- Water Removal: High concentrations of salt and sugar draw water not only from the food cells but crucially, from any microbial cells (like bacteria, yeasts, or moulds) present on or within the food.
- Dehydration: This process effectively dehydrates the microorganisms. Without sufficient water, their cellular processes slow down or stop entirely.
- Inhibition of Growth: The lack of moisture protects the salted food and prevents the growth of moulds or other pathogens. Microorganisms require water to grow and reproduce. By making the water unavailable (binding it to the salt or sugar molecules and drawing it out), the hypertonic environment prevents them from multiplying and spoiling the food.
Essentially, salt and sugar make the food an inhospitable place for spoilage-causing microbes due to the scarcity of available water, extending the food's shelf life.
