Whey is the liquid part of milk, everything that is left over when curds form during cheese-making. That’s right, whey is what used to be called a waste product, and was dumped by the ton. No longer. A chemical analysis of whey would show that it retains most of milk’s minerals and water-soluble vitamins, along with the bulk of the milk’s sugar. Whey therefore is sweet, health-packed, relatively fat-free, and cheap.
Once manufacturers discovered that they could give their products that good milky taste and feel at a fraction of the cost of whole milk, they started using whey in everything. Whey is in the vast majority of cookies, and can be found in uncountable numbers of frozen foods, cold cuts, salad dressings, and canned soups. There are many categories of supermarket foods in which it is difficult to find a product that does not use whey.
The news isn’t all bad. Because whey is a powder, it’s often used in very small quantities. If whey is one of the last items on an ingredients list, those of you who can have some milk probably can just pay it no never mind.
If you’re extremely sensitive, you should probably avoid any product that contains whey or any of its derivatives (sweet dairy whey, whey protein concentrate, reduced minerals whey, dried dairy blend, even the so-called reduced lactose whey) on its ingredients list.