Whey, also known as milk plasma, is a liquid that remains after milk has been curdled and strained, often produced as a by-product during cheese or casein manufacturing. Sweet whey is obtained from the production of rennet-based hard cheeses such as Cheddar or Swiss, while acid whey, also called sour whey, is obtained from the making of acid-based cheeses like cottage cheese.
In the past, whey was a popular drink in inns and coffee houses. Today, whey is widely used in the food industry due to its excellent nutritional properties and is often utilized in health, slimming, and clinical foods as a functional ingredient.