A definition of pH is the measurement of the acidity or alkalinity of a solution commonly measured on a scale of 0 to 14. pH 7 is considered neutral, with lower pH values being acidic and higher values being alkaline or caustic. pH is the most common of all analytical measurements in industrial processing and since it is a direct measure of acid content [H+], it clearly plays an important role in food processing. Among the reasons for measuring pH in food processing include:
•To produce products with consistent well defined properties
•To efficiently produce products at optimal cost
•To avoid causing health problems to consumers
•To meet regulatory requirements
Due to the logarithmic nature of the measurement, even small changes in pH are significant. The difference between pH 6 and pH 5 represents a ten-fold increase in acid concentration; a change of just 0.3 represents a doubling of acid concentration. Variations of pH can impact flavor, consistency, and shelf-life.
Regulatory bodies such as the departments of health often impose a certain value for the pH of the sanitation solution to be used. For example, the pH should be between 8 and 10 based on the chlorine concentration. Similarly, an iodine solution is meant to have a pH value of 5 or lower.
Milk and Dairy Products: pH of milk is around 6.8 and it is tested for impurities and signs of infection upon collection as well as at point of delivery. In processes such as sterilization, pH is checked since a lower value helps to speed up the process. However, lower pH levels can indicate that the cattle carried leukocyte infections such as mamites.
Milk used for cheese manufacturing must be of excellent quality and its pH value contributes to whether the cheese will be soft or hard. pH is also checked during cheese preparation, souring of milk and cream maturation. Pathogen multiplication of the fresh and soft variety, is slowed down considerably by ensuring that the pH stays in the 4.1 to 5.3 region.
Controlling the pH value is very important in butter manufacturing processes. For example, cream is cooled after pasteurization at a very strict pH value of 6.70 to 6.85 to generate sweet butter. In order to manufacture sour butter, citric acid extracts are added to acidify the cream to 4.6-5.0 pH. With butter having a high diacetyl content, a starter is added to bring the pH value to around 5. As with other products, a lower pH value enhances the shelf life of the product.
With yogurt production, the cooling of cultured milk can start only once acidification has reached a pH value of 4.4 to 4.6. As for fruity yogurts, the pH value of the added fruit must be the same as the yogurt itself to avoid undesirable reaction at the end of the cycle. The finished product should ideally have a pH of 4.0 to 4.4 for longer conservation.
Even small changes in the pH value of spring or well waters can indicate a possible fouling of the natural strata. Where municipal water is used, it is often pretreated and its pH monitored. In making fruit juices, the pH of sugar extracts as well as those of juices during purification and refining are checked.
pH plays a crucial role in the production of beer. For example the pH value of crushed malt is around 5.8 whereas its ideal value for protein decomposition is around 5.5. To ensure a consistent quality, the pH of brewed beer prior and after bottling is regularly monitored.
pH of wine normally ranges from 2.8 to 3.8 with the pH influencing various stages of the process including fermentation and conservation. With the pH exceeding 3.5, certain bacteria can attack the wine. However, taste of wine also depends largely on its pH value with acidic wines becoming dry.
pH can be used as an indicator for meat quality ranging from 5.4 to 7.0, can also provide an indication of whether fresh meat was properly stored as varies in different parts of the animal based on the muscular mass, for example, the loin has a lower pH value. Too high a pH value induces a loss of aroma and a visibly darker meat resulting in a lower market value. In addition to meat, ingredients used in the production of ham and sausages are often refrigerated. By simply checking the pH at the liquefier’s intake and drainage points, one can determine if any ammonia has leaked out.
Polluted water can pass on toxins, even fatal ones, to shellfish. The fact that shellfish such as oysters are often consumed raw poses a greater health hazard. As a result, farmed or natural shell fish is detoxified with several wash cycles. The pH of the wash water is an excellent indication whether the process has been properly completed.
A pH value of 4.0 to 5.8 is recommended for baked bread in order to prolong its shelf life. Batter has to be acidified to a pH of 4.1 or less to ensure that pathogens are not multiplied. Otherwise it must be kept at temperatures below 5°C.
For marmalades and syrups this is around 3.5 whereas for caramels it is in the 4.5-5.0 pH range. pH is also checked during the various processes including the gelatinization of jams and marmalades as well as purification and refining of juices in pre-separation and saturation phases. Pasteurized items and cold salads often have a pH value of 5.3. By adding a small quantity of vinegar or lemon juice, sauces such as mayonnaise are acidified and their pH is lowered to 4.1 to prolong their shelf life.
A pH value of 2,5 to 5.5 tends to prolong the shelf life of fresh fruit and inhibit the multiplication of micro-organisms. Likewise for vegetables with a more neutral pH in the 4.6 to 6.4 range.
Checking the pH of water prior to adding it to different food processes provides a quick and simple way to guarantee the quality of the end-product. This is particularly so since the quality of water taken from the municipal water system or underground water tables vary considerably over time. Consequently, lack of proper control at an initial stage can have a detrimental effect on the consistency of the end-product.
pH plays an important role in food processing whether the objective is to make sour bread not too sour, cheese with a bite, or beer that is just right. Constant pH measurement and controlled addition of buffering agents compensates for intangible process variations and assures reliable product quality. Sper Scientific offers a complete line of pH meters and probes that provide a reliable and accurate measurement of pH. Below are few of these meters: