Yogurt is a semi-solid or thickened milk product that has a custard-like consistency due to the presence of live bacterial cultures that ferment the milk sugars (lactose) in the milk. While yogurt contains a significant amount of liquid, it is not considered a fluid for most purposes.
In terms of food regulation, the definition of fluid varies depending on the context. In the United States, for instance, the Food and Drug Administration (FDA) defines fluid milk as milk and milk products that have not been subjected to a process that removes water or milk solids. Under this definition, yogurt would not be considered a fluid milk product because it has undergone a fermentation process that thickens the milk and reduces its water content.
Similarly, in the European Union, the classification of milk products as fluids or non-fluids is based on the fat content and viscosity of the product. Fluid milk products are defined as those with a fat content of less than 10% and a viscosity of less than 150 mPa·s at 20°C. Yogurt, being a thickened milk product, has a higher viscosity than fluid milk and would therefore be classified as a non-fluid milk product.
From a nutritional perspective, yogurt can be considered a fluid due to its high water content. The water in yogurt contributes to its overall volume and weight, and also affects its nutrient content. For instance, the water in yogurt dilutes the calorie and nutrient density of the product, making it lower in calories and nutrients per gram than more concentrated dairy products like cheese.
In conclusion, whether yogurt is considered a fluid or not depends on the context in which the term is being used. From a food regulation perspective, yogurt is generally not considered a fluid because it has undergone a fermentation process that thickens the milk and reduces its water content. However, from a nutritional perspective, yogurt can be considered a fluid due to its high water content.