Whey

Whey or milk serum is the liquid remaining after milk has been curdled and strained. It is a by-product of the manufacture of cheese or casein and has several commercial uses. Sweet whey is manufactured during the making of rennet types of hard cheese like cheddar or Swiss cheese. Acid whey (also known as "sour whey") is a by-product produced during the making of acid types of dairy products such as cottage cheese or strained yogurt.

Production
To produce cheese, rennet or an edible acid is added to heated milk. This makes the milk coagulate or curdle, separating the milk solids (curds) from the liquid whey. Sweet whey is the byproduct of rennet-coagulated cheese and acid whey (also called sour whey) is the byproduct of acid-coagulated cheese. Sweet whey has a pH greater than or equal to 5.6, acid whey has a pH less than or equal to 5.1.

Uses
Whey is used to produce whey cheeses such as ricotta, whey butter, so-called brown cheeses such as Brunost (technically not cheeses at all), and many other products for human consumption. It is also an additive in many processed foods, including breads, crackers, and commercial pastry, and in animal feed. Whey proteins consist primarily of α-lactalbumin and β-lactoglobulin. Depending on the method of manufacture, whey may also contain glycomacropeptides (GMP).

Dairy whey remaining from home-made cheesemaking has many uses. It is a flour conditioner and can be substituted for skim milk in most baked good recipes that require milk (bread, pancakes, muffins, etc.).

Whey protein (derived from whey) is often sold as a nutritional supplement. Such supplements are especially popular in the sport of bodybuilding. In Switzerland, where cheese production is an important industry, whey is used as the basis for a carbonated soft drink called Rivella. In Iceland, MS manufactures and sells liquid whey as Mysa in 1-liter cartons (for 100 g: energy 78 kJ or 18 kcal, calcium 121 mg, protein  0.4 g, carbohydrates  4.2 g,  sodium 55 mg).

Throughout history, whey was a popular drink in inns and coffee houses. When Joseph Priestley was at college at Daventry Academy 1752–1755, he records that, during the morning of Wednesday 22 May 1754, he “went with a large company to drink whey.” This was probably ‘sack whey’ or ‘wine whey.'

Another use of whey is to make ‘Cream of Tartar Whey’: "Put a pint of blue milk [blue milk is characterized by the appearance on its surface, eighteen or twenty-four hours after it is drawn, of small, indigo-blue fungal spots that rapidly enlarge until the whole surface is covered with a blue film.] over the fire, when it begins to boil, put in two tea spoonfuls of cream of tartar, then take it off the fire, and let it stand till the curd settles to the bottom of the pan, then put it into a basin to cool, and drink it milk warm.”

Whey was also used in central Spain to enrich bakery products. In some traditions, it was used instead of water to produce bread dough.

In areas where cheese is made, excess whey byproduct is sometimes sprayed over hay fields as a fertilizer.

Whey cream and butter
Cream can be skimmed from whey. Whey cream is more salty, tangy, and “cheesy” than ("sweet") cream skimmed from milk, and can be used to make whey butter. Whey cream and butter are suitable for making butter-flavoured food, as they have a stronger flavour of their own. They are also cheaper than sweet cream and butter.

Health
Because whey contains lactose, it should be avoided by those who are lactose intolerant. Dried whey, a very common food additive, contains 76.9% lactose. When used as a food additive, whey can contribute to quantities of lactose far above the level of tolerance of most lactose-intolerant individuals.

Liquid whey contains lactose, vitamins, protein, and minerals, along with traces of fat. In 2005, researchers at Lund University in Sweden discovered that whey appears to stimulate insulin release, in type 2 diabetics. Writing in the American Journal of Clinical Nutrition, they also discovered that whey supplements can help regulate and reduce spikes in blood sugar levels among people with type 2 diabetes by increasing insulin secretion.

Individuals can also be whey intolerant, meaning that they can handle forms of cheese or milk that drain out excess whey. The whey protein can be altered by high heat, which means that forms of milk that have been altered are more likely to be tolerated by whey intolerant individuals. This can include evaporated or boiled milk, as well as milk powder.

Protein
Whey protein is the name of globular proteins that can be isolated from whey. It is typically a mixture of globinstagers beta-lactoglobulin (~65%), alpha-lactalbumin (~25%), and serum albumin (~8%), which are soluble in their native culture forms, independent of pH.