Milk whey liquid is the fluid left over from the process of cheese making. During the manufacture of cheese, milk proteins are coagulated using either an enzyme called rennet or an acid, such as citric acid. The coagulated protein – primarily casein – forms the basis of cheese, while the remaining liquid contains soluble whey protein as well as other nutrients. The nutritional value of sweet whey, obtained from rennet coagulation, differs slightly from that of acid whey, the product of acid coagulation.
The predominant nutrient in milk whey liquid is carbohydrates in the form of lactose, or milk sugar. A 1-cup serving of both sweet whey and acid whey contains nearly 13 g of carbs, accounting for three-fourths of its roughly 60 calories. Your body burns carbs as its primary fuel source, with all the cells of your body able to derive energy from the carbs in whey.
Milk whey liquid contributes several minerals to your diet, with differences depending on the milk coagulation process. For example, 1 cup of acid whey provides 250 mg of calcium and 200 mg of phosphorus, or 25 percent of your recommended daily intake of these minerals, while sweet whey gives you only about half this amount. Acid whey supplies approximately 10 percent of your daily need for zinc, and sweet whey offers one-third of this. Both forms supply your diet with roughly 7 percent of your daily potassium and magnesium.
The vitamin content of milk whey liquid is equivalent for both sweet and acid whey. A single cup of fluid contributes 30 percent of your daily requirement for riboflavin, 20 percent for both pantothenic acid and vitamin B-12, and just under 10 percent for thiamine and vitamin B-6. Milk whey liquid also contains a minor amount of niacin.
Although whey protein supplements are concentrated and therefore enriched with protein, milk whey liquid contains relatively little protein. A 1-cup portion supplies your diet with approximately 2 g of this macronutrient. Despite its low level, however, the protein in this liquid is high-quality, meaning it contains all the essential amino acids, or protein-building blocks, you need from your diet every day.
Sweet whey contains more milk fat than acid whey, with 1 cup of sweet whey offering nearly 1 g of fat compared with less than 0.25 g in acid whey. However, both forms of whey are quite low in this nutrient and contribute little to your dietary fat intake. Whey liquid originating from high-fat milk tends to have a higher fat content than that from low-fat milk, but high-fat whey is typically defatted through further processing.