Columbia, MD -- The Greek, sometimes referred to as strained, yogurt category in the US has exploded onto the scene causing significant disruption in the overall refrigerated yogurt market. Greek yogurt accounts for some 44% of the total yogurt category sales value in the US, up from just 4% in 2008.
A typical, modern manufacturing process for Greek yogurt involves high heat treatment of skim milk, inoculation with thermophilic cultures, fermentation, and whey separation. In addition to substantially reducing the indigenous microbial population of the milk, the severe heat treatment induces thermochemical bonding of milk serum proteins with casein as well as serum protein aggregation. A continuous gel matrix forms as the fermentation proceeds through the isoelectric points of the various proteins. Whey is separated from the white mass utilizing either centrifugal separation or Ultrafiltration.
Approximately three pounds of skim milk yields approximately one pound of Greek yogurt while the remaining two pounds is the acid whey byproduct. In contrast to sweet whey, this acid whey byproduct has been substantially depleted of serum or whey proteins, resultant from the temperature treatment described above, and lactose as a result of the lactic acid fermentation. Additionally this acid whey contains accumulations of milk minerals, lactic acid, and galactose, an unfermentable epimer of glucose, all resulting from the fermentation process.
Current outlets for this low-value byproduct are therefore limited to land application as fertilizer, bovine and/or porcine feed, or feedstock for anaerobic digestion for gas production. Because the whey volume represents about two-thirds of the incoming milk volume, transportation cost for returning the acid whey to field or farm represents a significant expense.
As an interim step toward developing a more value-added solution, GEA Filtration has successfully commercialized the use of Reverse Osmosis (RO) to concentrate the acid whey by a factor of three to four, thereby reducing transport cost proportionally. The RO permeate is further purified in a Polisher (ROP) to produce recovered water for re-use within the factory. In addition to reducing the transportation cost of acid whey disposal, the concentrated whey has a higher nutritional density than the un-concentrated precursor and provides some opportunity for producing a small revenue stream from the animal feed application.
Bruce Blanchard - National Sales Manager, GEA Filtration
GEA Process Engineering Inc.
Phone +1 715 377 0533, Fax +1 715 386 9376
www.gea.com / www.geafiltration.com