What it is
Casein is the main protein in cow's milk, and caseinate, its sodium or calcium salt, is the same thing processed for texture and melt. US law lists milk among the major food allergens, and casein is one of the milk-derived ingredients that labelling is meant to flag. Because it comes straight from milk, it is not vegan.
Where it hides
Casein is the classic gotcha in products that sound plant-based. It shows up in some non-dairy coffee creamers, where non-dairy is a marketing term rather than a promise, and in a handful of melty plant-styled cheeses that use caseinate for stretch. Protein bars and powders lean on it too. The dairy trio to scan for together is casein, whey and lactose.
How it is made
Casein is about 80 percent of the protein in cow’s milk, whey being most of the rest. To make sodium or calcium caseinate, processors acid-precipitate the casein out of skimmed milk, wash it, then redissolve it by neutralising with sodium or calcium hydroxide. What comes out is a fine, water-soluble powder with no lactose and almost no milk fat. Manufacturers want it for solubility and body, not for dairy flavour, which is why it appears under its chemical name rather than as milk.
The non-dairy loophole
There is no real ambiguity about what caseinate is. The complication is entirely in the labelling. A US product can legally be called non-dairy while containing caseinate, because the regulatory meaning of non-dairy descends from decades-old rules about milk fat rather than from any absence-of-milk-protein standard. Anyone reading non-dairy as a synonym for dairy-free is leaning on marketing shorthand that the FDA’s own definitions do not support. Dairy-free and vegan are the claims that mean what they appear to mean.
Powdered and liquid coffee creamers are the classic case, since caseinates give body and stop the oily separation that happens when vegetable oil meets hot coffee. Non-dairy whipped toppings use the same trick. Caseinate also turns up as a binder or melt booster in some processed cheese, deli meat, protein bars and the imitation cheese blends used commercially on pizza, because casein is specifically what gives real cheese its stretch.
How to tell
Allergen law does the work here, and it is on your side. Milk is one of the nine major allergens US manufacturers must declare in plain language, so casein or caseinate has to carry a note identifying its dairy origin or be captured in a Contains statement, whatever the front of the pack claims. In the UK and EU, milk is one of the 14 allergens that must be visually emphasised wherever it appears, including inside the word caseinate. The word milk stays findable even in a long ingredient list.

