Food Preservation

Step 1: Understanding the Concept:
The question asks for the primary function of a refrigerator, a common household appliance.

Step 2: Detailed Explanation:
- Refrigeration: This is the process of making and keeping things (especially food and drinks) cool by storing them in a refrigerator. The low temperature slows down the growth of bacteria and other microorganisms, thus preserving the food for a longer time. The name "refrigerator" itself points to this function.
- Fermentation: This process, used to make things like yogurt or bread, often requires a warm environment to encourage microbial growth, which is the opposite of what a refrigerator does.
- Dehydration: This is the process of removing water or moisture from food, often using heat or air circulation, which is not a function of a standard refrigerator.

Step 3: Final Answer:
A refrigerator is used for refrigeration.

Step 1: Understanding the Concept:
Food preservation involves treating and handling food to stop or slow down spoilage (loss of quality, edibility, or nutritional value) and thus allow for longer storage. The goal is to inhibit the growth of bacteria, fungi, and other microorganisms.

Step 2: Detailed Explanation:
- Dehydration (Drying): This method involves removing water from the food. Microorganisms need water to grow, so removing it prevents spoilage.
- Freezing: This method lowers the temperature of the food to below 0 C, which stops the growth of most microorganisms and slows down enzymatic activity.
- Canning: This method involves heating food to a high temperature to kill microorganisms and then sealing it in an airtight container (can or jar) to prevent new microorganisms from contaminating it.
All three are well-established and effective methods of food preservation.

Step 3: Final Answer:
Dehydration, freezing, and canning are all methods of food preservation. Therefore, the correct option is All of these.

Step 1: Understanding the Concept:
A food preservative is a substance that is added to food to prevent or slow down spoilage caused by microbial growth or undesirable chemical changes.

Step 2: Detailed Explanation:
- Salt: Used in curing meats and pickling. It draws water out of microbial cells through osmosis, killing them or inhibiting their growth.
- Sugar: Used in high concentrations in jams, jellies, and preserves. Like salt, it works by osmosis, reducing the amount of free water available for microorganisms.
- Oil: Used in pickles. It creates a layer on top of the food that cuts off the air supply, preventing the growth of aerobic bacteria and molds.
All three are common, traditional household preservatives.

Step 3: Final Answer:
Salt, sugar, and oil are all used as food preservatives.