What method of food preservation involves bacteria in milk producing lactic acid to turn it into yogurt?

The method of food preservation that involves bacteria in milk producing lactic acid to turn it into yogurt is fermentation. During fermentation, specific beneficial bacteria, such as Lactobacillus, convert lactose (the sugar in milk) into lactic acid. This process not only preserves the milk by creating a more acidic environment, which inhibits the growth of spoilage-causing microorganisms, but it also transforms the texture and flavor of milk into yogurt. The lactic acid produced thickens the milk and gives yogurt its characteristic tangy taste.

In contrast, the other methods listed do not involve this type of biological conversion. Freezing preserves food by slowing down enzyme activity and microbial growth, which does not involve lactic acid production. Dehydration removes moisture from food, which inhibits spoilage but does not utilize bacterial action. Canning involves heat treatment to kill bacteria and enzymes, rather than promoting bacterial fermentation, making each of these methods distinct from the fermentation process.