How does fermentation preserve food?

• A. Increases acidity via starter culture producing lactic acid; pH lowered by starter culture activity and by appropriate time/temperature factors
• B. Decreases acidity via lactic acid consumption
• C. Adds sugar to foods to preserve them
• D. Uses high heat to preserve foods

Answer: (D)

The main idea is that fermentation preserves food by creating an environment that’s hostile to spoilage organisms through acid production. In lactic acid fermentation, starter cultures (lactic acid bacteria) metabolize sugars and produce lactic acid, which lowers the pH of the food. That drop in acidity, along with the presence of the acids themselves, inhibits many spoilage and pathogenic microbes, helping the food stay safe longer. The extent of acidification depends on how long the fermentation runs and the temperature, which affect how much acid is produced.

High heat, on the other hand, is a different preservation method (like pasteurization or cooking) that kills microbes rather than relying on the fermentative acid environment. So fermentation preserves by acidifying the product, not by applying heat.