A Breakdown of Proteins in Curd vs. Whey
Also, What is Whey, Anyway?
When making goat cheese, you end up with most of the protein in curd and lactose in the whey, but we can get a bit more specific than that. Different cheese-making processes can give a slightly different composition of the leftover whey while leaving the curd essentially the same regardless of curdling method. The finished cheese product may even have some whey left inside rather than it all being separated out. But don’t necessarily throw out your leftover whey; it has uses, too!
Properties of the Curd
The milk properties that end up in the curd are predominately fat-soluble elements. This includes the milkfat itself as well as the caseins. In various mammalian milks, there are typically three or four different caseins. They are lumped together because they are so similar in structure. Goat’s milk contains predominately beta-casein followed by alpha-S2 casein with significantly lower amounts of alpha-S1 casein. This alpha-S1 casein is the type predominately found in cow’s milk. In a typical cheese curd, the fat makes up roughly 30-33 percent of the total weight but can be as low as 14 percent. The protein in curd makes up roughly 24-25 percent of the total weight. These percentages can vary depending on the type of cheese, goat milk vs cow milk, its hardness, and how the milk was standardized before the cheese making process. Standardizing milk is when the fat content is adjusted by either adding or removing cream to reach a certain fat content desirable for a particular cheese. The curd also retains a large portion of the vitamins and minerals from the milk. These include calcium, vitamin B-12, vitamin B-6 (pyridoxine), vitamin D, vitamin A, and potassium.¹
Properties of the Whey
Whey is about 90 percent water. The solids in whey consist of whey proteins, lactose, hormones, growth factors, enzymes, vitamins, and minerals. There are many different whey proteins. The whey proteins found in the highest concentrations are beta-lactoglobulin and alpha-lactalbumin. Other whey proteins include immunoglobulins (also known as antibodies), lactoferrin, and serum albumin. Proteins compose approximately one percent of the total whey composition. When the water is removed leaving whey in powder form, the protein makes up 10 percent of the total dry solids. Lactose is the sugar of the milk. It is a disaccharide composed of glucose and galactose molecules. Lactose makes up 7-7.5 percent of the total whey composition or 70-75 percent when the whey is dehydrated to powder form. Of the vitamins and minerals that whey contains, the main ones found are calcium, vitamin B-1 (thiamine), vitamin B-2 (riboflavin), and vitamin B-6 (pyridoxine). There can also be trace amounts of fat or cream left in the whey after the curds have been separated out. This can be used to make whey butter. The level of lactose in the whey can be affected by the type of cheese-making process you use. When using starter cultures and rennet, you are left with what is called “sweet whey.” If you use acid to curdle the milk, you end up with “acid whey” or “sour whey” which has slightly lower lactose content.
Not All Cut and Dried
It seems simple to divide what goes into cheese curd and what remains in whey, but as you learn how to make cheese curds, it becomes apparent that cheese is not entirely curd. Some whey is retained for moisture content in the finished product. Different types of cheeses have varying amounts of residual whey. Cottage cheese, ricotta cheese, and similar types have the largest amount of whey left in the cheese product while very hard cheeses like Parmesan have very little whey left in them. This residual whey factors into the total protein in the cheese curd as well as nutritional value of the cheese including amount of sugar (lactose).
Uses for Whey
Roughly 38 percent of the solid matter in milk is protein. Of this total protein, 80 percent is casein and 20 percent is whey protein. When you make cheese and separate the whey, the protein in curd is not the only high quality protein that results from these endeavors. Whey protein is high in essential amino acids making it quality protein for many purposes. One of the most common uses for whey comes in the form of whey protein powder for nutritional supplementation. This can even be further broken down to whey protein isolates where the majority of the lactose is removed. Whey also makes an excellent binding agent in baked goods especially those made with whole grains. It has also been found to help slow the rate at which these baked goods go stale and acts as an emulsifier to disperse shortening and other fats in baking. This can actually reduce the amount of shortening needed in a recipe.²
While it may not be 100 percent cut and dried on which nutrients go and stay where, the general composition of curds and whey is relatively consistent. Curds are mostly casein and milkfat while whey is mostly water, lactose, and whey proteins. Both have various vitamins and minerals, and both have nutritional value and uses.
¹ Hurley, W. L. (2010). Milk Composition Proteins. Retrieved September 17, 2018, from Lactation Biology Website: ansci.illinois.edu/static/ansc438/Milkcompsynth/milkcomp_protein.html
² “Whey” Into Baked Goods. (2006, January 1). Retrieved September 22, 2018, from Prepared Foods: https://www.preparedfoods.com/articles/105250-whey-into-baked-goods