Not all whey originates from traditional cheese production giving 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
precipitation of the milk.
Lactic acid is very hygroscopic and thermoplastic and thus very difficult to
dry. Neu-tralization 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 animals may get digestive problems.
- NaOH is sometimes used, but is not recommendable, as Nalactate is
hygroscopic and thermoplastic. Further 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, but special precautions
should be taken 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.
Generally speaking, acid whey is more
difficult to dry than sweet whey, and addition of 0.1-0.3% free-flowing agent
such as Tixosil is recommended during the drying operation.