Fermentation is a process of converting carbohydrates into alcohol or acids by microorganisms, which is used to preserve food. It is not a principle of food preservation, but rather a method of food preservation.

Heating food during preservation is primarily done to kill microorganisms, such as bacteria, yeasts, and molds, that can cause food spoilage and pose a health risk.

Vacuum cooling is a method of rapidly cooling food by placing it in a vacuum chamber, which is not commonly used for food preservation. Refrigeration, freezing, and chilling are all methods of cooling food to inhibit microbial growth and extend its shelf life.

Drying food during preservation is primarily done to remove moisture, which inhibits the growth of microorganisms and extends the shelf life of the food. It also concentrates the flavors and nutrients in the food.

Freeze drying is a method of drying food by first freezing it and then removing the moisture through sublimation. It is not commonly used for food preservation, as it is an expensive and time-consuming process.

Fermentation in food preservation is primarily done to produce alcohol or acids, which inhibit the growth of microorganisms and extend the shelf life of the food. It also imparts a characteristic flavor and aroma to the food.

Propionic acid fermentation is not a type of fermentation commonly used in food preservation. Lactic acid fermentation, alcoholic fermentation, and acetic acid fermentation are all widely used to preserve foods such as yogurt, beer, wine, and pickles, respectively.

Adding salt to food during preservation is primarily done to inhibit the growth of microorganisms, as salt creates an osmotic environment that draws water out of microbial cells, preventing their growth and reproduction.

Smoking is a method of preserving food by exposing it to smoke from burning wood or other materials. It is not a method of adding salt to food, although it can impart a salty flavor.

Adding sugar to food during preservation is primarily done to inhibit the growth of microorganisms, as sugar creates a high osmotic environment that draws water out of microbial cells, preventing their growth and reproduction.

Pickling is a method of preserving food by submerging it in a brine solution, which is a mixture of water, salt, and sometimes vinegar or other acids. It is not a method of adding sugar to food.

Adding vinegar to food during preservation is primarily done to inhibit the growth of microorganisms, as vinegar's acidity creates an environment that is hostile to microbial growth.

Freezing is a method of preserving food by lowering its temperature to a point where microbial growth is inhibited. It is not a method of adding vinegar to food.

Adding spices and herbs to food during preservation is primarily done to improve the flavor and aroma of the food. While some spices and herbs may have antimicrobial properties, their primary purpose in preservation is to enhance the sensory qualities of the food.

Canning is a method of preserving food by heating it to a high temperature and sealing it in airtight containers. It is not a method of adding spices and herbs to food.