After the heat treatment, the yogurt mixture is cooled to 43-46 ºC prior to the addition of yogurt starter culture bacteria at a concentration of about 2 % (v/v). This temperature range is optimal for the thermophilic microorganisms used in the yogurt starter culture [16]. The typical standard yogurt culture consists of S. thermophilus and L. delbrueckii subsp. bulgaricus in 1:1 ratio. Inoculation of starter cultures usually takes place in a sealed hygienic stainless steel vessel. However, the place of fermentation is different to each other in set-and stirred yogurt manufacture. It is usually occurred in individual containers and in large hygienic stainless steel vats in set- and stirred yogurt manufacturing processes, respectively. Incubation temperature is maintained and monitored at optimal level throughout the fermentation process for few hours (2.5-3 h) until the pH and acidity reached their desired levels prior to discontinue the fermentation process by rapid cooling. During the fermentation process, due to the metabolic activity of the lactic acid bacteria used, lactose converts into lactic acid which coagulates milk proteins along with the production of certain volatile compounds that gives its characteristic flavor and aroma.