Which food preservation method relies on lowering pH?

The method that relies on lowering pH is fermentation. This biological process involves the conversion of sugars and other carbohydrates into acids, gases, or alcohol through the action of microorganisms such as yeasts and bacteria. In many fermentation processes, particularly those involving vegetables and some dairy products, the pH is lowered due to the production of organic acids, such as lactic acid or acetic acid. This reduction in pH helps to create an acidic environment that inhibits the growth of spoilage organisms and pathogens, thus preserving the food.

In contrast, other methods such as freezing, canning, or drying do not primarily focus on altering the pH to achieve preservation. Freezing works by slowing down the metabolic processes of microorganisms, canning involves heating food to kill bacteria and sealing it to prevent recontamination, and drying removes moisture to inhibit the growth of bacteria, yeasts, and molds. Each of these methods has its unique mechanisms for preservation, but fermentation specifically utilizes the lowering of pH as a key factor in the process, making it the correct answer.