The bacterial process used to make yogurt is called fermentation. During this process, specific bacteria, primarily Lactobacillus bulgaricus and Streptococcus thermophilus, are introduced to milk. These bacteria ferment lactose, the sugar present in milk, resulting in lactic acid, which thickens the milk and gives yogurt its tangy flavor. The fermentation process typically takes several hours at a controlled temperature. Besides providing yogurt with a unique taste and texture, fermentation also contributes beneficial probiotics that can improve gut health and digestion. This method has been used for centuries to preserve milk and enhance its nutritional value.