Applications in the Cheese-Making Process
Milk Concentration by Ultrafiltration
The possibility of using UF to preconcentrate milk before cheese making has been extensively exploited for a wide variety of cheeses (Henning et al., 2006). By this procedure, milk is concentrated at the desired level by keeping constant the whey proteins to casein ratio. Manufacturing cheese by UF technique is a well-consolidated technology, and currently a number of products are produced by this procedure.
The advantages of UF concentrated milk in cheese making compared to traditional methods are decreases of the production costs thanks to standardization of cheese quality, higher yield, and manufacturing efficiency. Increase in yield is achieved by better retention of milk solids (mainly whey proteins) and moisture in cheese, and is strongly related to the extent by which milk volume is reduced (the concentration factor, CF). Improvement of manufacturing efficiency can be defined in terms of reduced energy and equipment requirements, lesser rennet and starter culture amounts, and decreased wastewaters volumes.
Ultrafiltration can be approached according to two different strategies: production of milk retentates, or standardization of milk composition. Retentates can be produced by concentrating milk by a factor varying from 1.2 to about 2 (low CF), from more than 2 to 5 (medium CF), to more than 5 (high CF). Standardization of milk composition is performed with the aim of keeping constant the protein concentration and the fat/ protein ratio throughout the year. By means of standardization, it is possible to overcome the problem of continuous adjusting the processing parameters by the cheese makers that are made for balancing the seasonal variations of milk composition. This goal is commonly pursued by applying a low concentration factor for reaching a protein concentration of 3.7% to 4.5%; the contemporary adjustment of the fat content (skimming or cream addition) also allows to keep constant the fat/protein ratio (commonly, the value ranges from 1.0 to 1.1). The main benefits of low concentration lay in increased capacity of the cheese vats and better utilization of plant equipment. Nevertheless, recent research indicates that a yield enhancement can also be obtained if proper modifications are made to the cheese-making protocol. Such modifications should be directed to increase the moisture content of the curd, in order to full valorize the better retention of milk total solids (Guinee et al., 2006). For the production of UF retentates, medium or high concentration factors are used: When high CF is applied, the final product is a sort of liquid pre-cheese that could need specific equipment to be processed. The best results in terms of yield are obtained by applying a concentration factor more than 6, in which cheese milk is concentrated to the total solids content in the final cheese. The oldest protocol dates from 1969 and allowed a cheese yield increase of 15% to 20% as a result of whey proteins retention in curd and higher humidity (Maubois et al., 1969). By this method, there is no whey drainage, and the cheese can be manufactured without the need for a vat. It is used to produce very soft cheeses such as quark, ricotta, and mascarpone, whereas it is unsuitable for medium- and long-ripened cheeses, as the compositional modifications give rise to structural defect and abnormal proteolysis (Brandsma & Rizvi, 2001; Pouliot, 2008). The highest CF (about 7), with strong enhancement of cheese yield, is applied in the APV-SiroCurd process; it requires specific plants because some further whey has to be expelled after coagulation. This procedure is suitable for the manufacturing of semi-hard cheeses such as feta, camem- bert and brie, but also of harder types such as cheddar (Fox et al., 2000).