Preservatives
7 Minutes
Food preservation for kids: learn why food spoils and how pickling, sugaring, drying, and freezing keep food safe. A science lesson in English.
- Why microbes need moisture, air, and nutrients to spoil food
- Pickling using salt and oil, and fermentation pickling in sauerkraut
- Preserving food by sugaring, boiling, drying, freezing, and canning
What this lesson teaches
Food preservation is the process of protecting food from microorganisms and preventing decay. Microbes spoil food because meals provide the moisture, air, and nutrients that these tiny organisms need to feed, multiply, and grow.
Why food spoils
Food provides an ideal habitat for microscopic organisms. When bacteria and other microbes land on fresh dishes, they feed on the available nutrients and reproduce rapidly as long as water and air are present. This rapid growth alters the food and causes it to rot, which is why untreated items like fresh tomato chutney can spoil in just a single day.
Pickling methods
Pickling prevents decay through two different methods. In chemical pickling, foods such as sliced mangoes are mixed with salt, spices, and oil before being sealed in a container. The salt draws out moisture, while the oil cuts off all contact with air, removing two conditions microbes need to survive. In fermentation pickling, food is kept in a liquid that prevents bad bacteria from multiplying while allowing good bacteria to thrive. An example is sauerkraut, where shredded cabbage is preserved by Lactobacillus bacteria that produce lactic acid, a dish relied upon over two thousand years ago by workers building the Great Wall of China.
Sugaring and moisture removal
Sugaring has been used since the eighteenth century to preserve cut fruits and vegetables. Pieces of fruit are combined with boiled sugar syrup and sealed inside tight containers. Concentrated sugar works like salt by absorbing moisture from the food, leaving no water for microbes to use. Honey naturally lasts for long periods without spoiling for this same reason, as it contains very little water and a high concentration of sugar.
Temperature, drying, and sealing methods
- Boiling exposes food to high heat, which kills microbes and keeps liquids like milk from turning bad quickly.
- Drying removes moisture completely, preventing microorganisms from growing on items like dried fruits.
- Freezing stores food at low temperatures where microbes cannot actively reproduce.
- Salting involves coating items like raw fish in salt to draw out all internal water.
- Canning packs food into sealed containers to lock out air, just as thick oil layers protect cooked tomato thokku.