What is one method used to preserve food by altering its pH?

Curing is a method used to preserve food that involves the application of salt or other ingredients to draw moisture out, which in turn alters the food's pH. This change in pH can create an environment that is less conducive to the growth of spoilage organisms and pathogens, effectively extending the shelf life of the food. Ingredients like nitrates and nitrites often used in curing help to further inhibit the growth of harmful bacteria and also add flavor and color to the food.

While other methods such as smoking, packaging, and cooling may play significant roles in food preservation, they do not primarily focus on altering the pH. Smoking involves exposure to smoke from burning or smoldering materials, which adds flavor and can also have some antimicrobial effects, but it does not significantly change the pH level of the food. Packaging helps to protect food from external contaminants but does not typically alter its pH. Cooling reduces the temperature to slow down the growth of microorganisms but does not impact the pH directly. Thus, curing stands out as the method that directly modifies the pH of the food to aid in preservation.