The pH scale measures how acidic or alkaline a substance is, ranging from 0 to 14. Values below 7 indicate acidity, with lower numbers being stronger acids. Values above 7 signify alkalinity, where higher numbers denote stronger bases. A pH of 7 is neutral. Fresh, healthy cow’s milk typically exhibits a pH value between 6.4 and 6.8, positioning it as slightly acidic but close to neutral.
What Affects Milk’s pH
The pH of milk is not constant and can change due to several factors, with microbial activity being a primary influence. Lactic acid bacteria (LAB), naturally present in milk, ferment lactose into lactic acid. This causes the milk’s pH to drop, making it more acidic and eventually leading to spoilage, characterized by a sour taste and curdling. Refrigeration and pasteurization slow the growth of these bacteria, but they do not eliminate them completely.
The health of the dairy animal also plays a role in milk pH. Mastitis, an inflammation of the udder, can cause a slight increase in milk pH, making it more alkaline. This occurs because inflammation increases the permeability of blood capillaries in the udder, allowing alkaline blood components to transfer into the milk. A higher pH in raw milk can sometimes indicate an udder infection.
Processing methods can intentionally or unintentionally alter milk pH. Pasteurization, a heat treatment, generally has a minimal effect on milk pH. However, fermentation processes, used to produce dairy products like yogurt and cheese, intentionally lower the pH. In these processes, specific lactic acid bacteria convert lactose into lactic acid, which is essential for the final product’s texture, flavor, and preservation. Milk from different animal species also naturally varies slightly in pH; for example, cow’s milk is 6.4-6.8, while sheep milk can be more acidic, and human milk is closer to neutral.
Why pH is Important for Milk
Monitoring milk pH is important for ensuring product quality and safety throughout the dairy industry. A dropping pH serves as a reliable indicator of milk freshness and the onset of spoilage. As lactic acid bacteria grow and produce more acid, the pH decreases, signaling bacterial proliferation. This allows producers and consumers to identify milk that is no longer fresh.
The control of pH is important in the creation of fermented dairy products. For instance, in yogurt production, the pH needs to drop for milk proteins to coagulate, forming the characteristic thick texture and tangy flavor. Similarly, cheese making relies on specific pH levels to facilitate curd formation and influence the final flavor and texture profiles. Maintaining consistent pH levels during processing is important for achieving uniform product consistency and quality. Significant deviations in pH can also indicate milk that may be unsafe for consumption.