Greek yogurt differs from other yogurts because it goes through a straining process to remove the whey. Whey is a liquid that contains lactose, a natural sugar found in milk.Strained yogurt, Greek yogurt, yogurt cheese, sack yogurt or kerned yogurt is yogurt that has been strained to remove most of its whey, resulting in a thicker consistency than normal unstrained yogurt, while still preserving the distinctive sour taste of yogur