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.