Whey contains salts, approximately 10 % of the dry matter. Either as a natural component originating from the milk (with a transfer coefficient of 35 %, 65 % will end up in the whey) or salts used for various reasons during the cheese process (CaCl2 and/ or NaCl). The total salt content can be so high that it is considered unsuitable for animal feed or as an ingredient for leaking purpose and definitively too high for baby food production. Production of demineralized whey powder (30- 90 % demineralized) can therefore become very important.
Demineralization of whey powder
Demineralization of whey can be done with different methods. Generally speaking, the more demineralized the whey is the easier becomes the drying becomes. The same drying technology as used for drying sweet whey is used.
The ion exchange process
Nanofiltration is a membrane filtration process. Water and the monova-lent ions like Na+, Cl÷ and K+ pass through the membranes. A demineralization of approx. 40 % and a concentration from 6 % to 20-24 % total solids is achieved. The degree of demineralization can be increased, but it will result in higher loss of lactose.
Whey is passed through two lots of resins where the salts are removed. When the resins are saturated with salt, they are regenerated using acid and alkali. A typical cycle is two hours' production and four hours' regeneration. It is possible to reach 90-98 % demineralising. The process is performed at temperatures below 10 °C and no bacteriologic growth is experienced.
In an electrodialysis plant, a number of ion-selective membranes made from approximately the same material as the resins used in ion exchange are applied in the form of cells. Each cell, consisting of one cationic and one anionic membrane, is arranged in a stack analogous to a plate heat exchanger.
To obtain sufficient conductivity of the whey to be treated a pre-concentration to 20-28 % solids, as well as a processing temperature of 30-45 °C, is necessary. The recirculation time depends on the required demineralization level and may reach up to 6 hours if 90 % demineralizing is the goal. Naturally, this results in bacteria growth. To avoid this, the temperature may be lowered which will result in an increased plant size.