Food preservation is the science of slowing spoilage so food stays safe, nutritious, and appealing for longer. It matters because microorganisms such as bacteria, yeasts, and molds can grow on food and sometimes cause illness. Preservation methods also help reduce food waste and make seasonal foods available year-round.
In nutrition and health science, safe preservation protects both the energy value and the nutrients in food.
Key Facts
- Refrigeration slows microbial growth because lower temperature reduces enzyme activity and cell metabolism.
- Freezing preserves food by turning water into ice, which makes less liquid water available for microbes.
- Water activity, written as aw, measures how much water is available for microbial growth.
- Most bacteria grow best near pH 6.5 to 7.5, while many preserved foods use acid to lower pH below 4.6.
- Pasteurization uses controlled heat to reduce harmful microbes, such as heating milk to 72°C for 15 s.
- The danger zone for many perishable foods is about 4°C to 60°C, where bacteria can multiply quickly.
Vocabulary
- Microorganism
- A tiny living thing, such as a bacterium, yeast, or mold, that can grow on food and sometimes cause spoilage or disease.
- Pasteurization
- A heat treatment that kills or reduces harmful microbes in foods and drinks while limiting changes in flavor and nutrition.
- Water activity
- A measure of how much water in a food is available for microbes to use for growth.
- Fermentation
- A preservation process in which helpful microbes change sugars into acids, alcohol, or gases that can improve safety, flavor, and texture.
- Oxidation
- A chemical reaction with oxygen that can cause fats, colors, and vitamins in food to break down.
Common Mistakes to Avoid
- Assuming the refrigerator kills all microbes is wrong because cold temperatures mainly slow growth, and some organisms can survive or grow slowly.
- Using damaged or bulging cans is unsafe because gas buildup or broken seals can signal microbial growth and possible toxin production.
- Thinking drying food removes all risk is wrong because dried foods can absorb moisture again, allowing molds or bacteria to grow.
- Adding a little vinegar without measuring pH is unreliable because safe acid preservation depends on reaching a low enough pH throughout the food.
Practice Questions
- 1 A student cools soup from 70°C to 20°C in 3 hours. What is the average cooling rate in °C per hour?
- 2 A dried fruit sample has a mass of 120 g before drying and 84 g after drying. How many grams of water were removed, and what percent of the original mass was lost?
- 3 A jar of vegetables is preserved by adding salt and acid, then sealing it. Explain how salt, low pH, and sealing each help reduce spoilage or foodborne illness.