Not all whey originating from traditional cheese production give sweet whey with a pH of min. 6.3. Cottage cheese, quark, Fromage Frais, Queso Fresco, Mozzarella, or similar products give whey with a pH of 4.6 due to the lactic acid precipitation of the milk. Lactic acid is very hygroscopic and thermoplastic and thus very difficult to dry. Neutralization can be necessary (to a pH of 5.2-5.5), and the following neutralizing agents can be used:

• Mg (OH)2 forms Mg-lactate, which is a 'dry' salt and preferred by the end-users, as it does not result in dark colouring of the meat of the animals, typically calves, eating the product

• Ca (OH)2 is also usable, but as the content of Ca++ is already high in the acid whey, the ani-mals may get digestive problems.

• NaOH is sometimes used, but is not recommendable, as Na-lactate is hygroscopic and ther-moplastic. Furthermore, it discolours the meat from the animals fed with the product.

Acid whey from acidification by mineral acids like HCl or H2SO4 need not be neutralized. Special precautions should be taken though in the selection of the stainless steel used for the fabrication of the evaporator and spray dryer, as corrosion is a problem, especially due to the Cl- ions.

After the evaporation the concentrate is pre-crystallized before spray drying. Generally speaking, acid whey is more difficult to dry than sweet whey, and addition of 0.1-0.3 percent free-flowing agent, such as Tixosil, is recommended during the drying operation.