Whey protein comes from milk, specifically the liquid left over after milk is curdled during cheesemaking. For every kilogram of cheese produced, roughly 9 to 10 liters of liquid whey is generated. That thin, watery liquid is then filtered, concentrated, and dried into the powder sold as a supplement. What starts as a dairy byproduct ends up as one of the most popular protein sources in the world.
How Cheesemaking Creates Whey
Milk contains two main types of protein: casein and whey. Casein makes up about 80% of milk’s protein, and whey accounts for the remaining 20%. During cheesemaking, an enzyme or acid is added to milk, which causes the casein proteins to clump together into solid curds. The liquid that separates from those curds is whey.
The separation happens on flat screens and draining belts that catch the solid curds and let the liquid pass through. This liquid whey represents 85 to 95% of the original milk volume and carries more than half of milk’s total nutrients, including proteins, lactose (milk sugar), and minerals. In its raw form, liquid whey is mostly water, around 93 to 94%, with only about 6 to 10 grams of protein per liter. That’s why significant processing is needed to turn it into a concentrated protein powder.
There are two types of liquid whey depending on how the cheese was made. Sweet whey, with a pH above 5.6, comes from cheeses produced with enzymes. Acid whey, with a pH below 5.6, results from cheeses made with organic acids like those in yogurt or cottage cheese production. Sweet whey contains slightly more protein and lactose, while acid whey is higher in minerals. Most whey protein supplements are made from sweet whey.
From Liquid to Powder
Turning watery whey into a high-protein powder requires several steps. First, the liquid is passed through ultrafiltration membranes, which act like very fine sieves. These membranes let water, lactose, and minerals pass through while holding back the larger protein molecules. The more times the whey is filtered, the higher the protein concentration in the final product.
Once the protein is concentrated to the desired level, the liquid needs to be dried. Spray drying is the most common method in the dairy industry. The concentrated whey is atomized into tiny droplets and blasted with hot air inside a drying chamber. The water evaporates almost instantly, leaving behind a fine, porous powder with only 1 to 6% moisture. The inlet air temperature ranges from 160 to 255°C, which sounds extreme, but the rapid evaporation of water actually cools the droplets and prevents the proteins from breaking down. Each droplet spends only about 17 to 30 seconds in the chamber.
Freeze drying is an alternative that avoids heat entirely. The concentrated whey is frozen to around negative 40°C and then dried under vacuum for up to 30 hours. This preserves more of the protein’s original structure, but it’s slower and more expensive, so it’s far less common in commercial production.
Concentrate, Isolate, and Hydrolysate
The three main forms of whey protein you’ll see on store shelves differ in how much processing the whey undergoes after that initial separation.
- Whey protein concentrate (WPC) contains anywhere from 25 to 80% protein by weight. The two most common grades are WPC35 (about 34 to 36% protein) and WPC80 (about 73 to 83% protein). The rest is lactose, fat, and minerals. WPC80 is what most protein powders use. It’s produced through ultrafiltration under mild temperature and pH conditions, which keeps the proteins largely intact.
- Whey protein isolate (WPI) is filtered further using additional diafiltration steps, pushing the protein content to 90 to 95% by weight. This extra processing removes nearly all the lactose and fat, which makes isolate a better option if you’re lactose-sensitive. It also means fewer calories per gram of protein.
- Whey protein hydrolysate starts as concentrate or isolate, then gets treated with enzymes that break the protein chains into smaller pieces called peptides. The enzymes cleave the bonds between amino acids, creating fragments that are faster to digest. This form is commonly used in infant formulas and medical nutrition products, though some sports supplements use it as well.
What’s Actually in the Protein
Whey isn’t a single protein. It’s a mixture of several smaller proteins, each with different properties. The two most abundant are beta-lactoglobulin and alpha-lactalbumin, which together make up the bulk of whey’s protein content. The remaining fraction includes smaller amounts of immune-related proteins and growth factors, though these are present in much lower quantities and their significance in supplement form is debated.
What makes whey popular as a supplement is its amino acid profile. It’s particularly rich in branched-chain amino acids, which play a direct role in muscle protein synthesis. It’s also a complete protein, meaning it contains all nine essential amino acids your body can’t produce on its own.
Whey From Goat and Sheep Milk
Almost all commercial whey protein comes from cow’s milk, but goat and sheep milk produce whey too. The protein makeup differs between species. In goat milk whey, the dominant protein is alpha-lactalbumin, while sheep milk whey contains more beta-lactoglobulin. Sheep milk is also significantly richer in total protein (averaging 6.36%) compared to goat milk (2.75%), which means sheep whey yields more protein per liter.
In both goat and sheep milk, whey proteins account for roughly 15 to 17% of total milk protein, similar to the ratio in cow’s milk. Goat whey supplements are marketed to people who find cow’s milk difficult to tolerate, though both contain lactose and similar protein structures. These products remain niche and tend to cost significantly more than standard bovine whey.
Why It Was Once Thrown Away
For most of the history of cheesemaking, liquid whey was considered waste. With 9 to 10 liters generated for every kilogram of cheese, disposal was a real environmental problem. Dumped into waterways, whey’s high lactose content feeds bacteria that consume dissolved oxygen and harm aquatic ecosystems. The development of membrane filtration technology in the late 20th century transformed whey from a costly waste stream into a valuable commodity. Today, the global whey protein market is worth billions, and cheese manufacturers often earn as much from their whey as from the cheese itself.