pH is the measure of the degree of acidity or alkalinity of a substance, defined as the negative logarithm of the hydrogen ion concentration. The scale ranges from 0, very strongly acidic, to 14, very strongly alkaline, with a neutral solution such as pure water at 25 °C having a pH of 7. In food science, pH is one of the most critical parameters: it governs microbial growth, enzyme activity, protein functionality, flavor, and color. Acidic foods below pH 4.6 inhibit Clostridium botulinum, which underpins the safety of canned acid foods. Processors monitor pH during fermentation, pickling, and dairy manufacture, adjusting it with acidulants such as citric, acetic, or lactic acid to ensure safety and quality.