What In The World Is Whey?: Whey And Its Kashrus Explained

OU Kosher Staff

Most people aren’t quite sure what whey is. We know that whey is used in some baked products, that it is a principal ingredient in many nutritional products, and that it has something to do with curds (whatever that means!).

L’maaseh, what is whey, and are there any kashrus concerns?

The short answer is that whey is the protein-rich component of milk that remains behind when milk is made into cheese. There are plenty of kashrus concerns, and much hashgacha work is needed to obtain kosher whey.

And here is the long answer:
When milk is made into cheese, the “bulkiest” components of the milk (its casein protein and dairy fat) form into cheese curds, which are gelatinous protein matrices with fat entrapped therein. The cheese curd is dried somewhat, molded into blocks and made to look “nice”; the finished product is what we call cheese. The remaining liquid component of the milk that did not form into cheese curd is called whey. Whey, which is an opaque yellowish fluid (the natural color of milk once it is stripped of its casein protein and dairy fat), contains miniscule proteins called whey protein, some residual dairy fat, as well as lactose (dairy sugar) and minerals. Many companies remove the whey protein component and concentrate it, producing a protein-charged material called – you guessed it – whey protein concentrate, or WPC. WPC that is concentrated an extra 10% is called whey protein isolate, or WPI.

In theory, there should be absolutely no kashrus issues with whey, as it is, after all, mere milk components that never succeeded in becoming cheese. Furthermore, Chazal only decreed the issur of gevinas akum (cheese which is not supervised by a Yisroel and is hence non-kosher – v. Yoreh Deah 115:2) on actual cheese and not on whey; whey from gevinas akum production can therefore be kosher. Based on this halacha, nearly all kosher whey is derived from gevinas akum production; there is simply not enough gevinas yisroel (kosher-supervised cheese) production to provide the amounts of kosher whey that are needed, and it is not halachically necessary.

It would thus appear that whey should always be kosher. But, not so fast – it’s far from pashut, and here’s why:

  1. Some cheese contains non-kosher rennet enzymes (derived from neveilah [non-kosher] calf tissue). Should such enzymes be used in cheese-making, the resultant whey is deemed non-kosher. (ShuT Chasam Sofer Yoreh Deah 79) A kashrus agency that certifies whey must therefore assure that all enzymes (and other ingredients) used in the cheese-making process are kosher.
  2. Some varieties of cheese have hot contact with the gevinas akum curd while in the production vat. What this means is that the non-kosher ta’am (taste) of the gevinas akum curd is passed via heat transfer to the otherwise-kosher whey, rendering this whey non-kosher as well. Typical examples of this are some types of parmesan and Swiss cheese production, in which the vats and their contents are heated to well above 120˚ F degrees, causing a ta’am transfer from the cheese curd, that is being formed in the vats, into the whey that is also there and in direct contact with the cheese curds at the time. So too, the manufacture of some cheeses includes the spraying of very hot water onto the curds while they are still in the vat with the whey, toward the end of the production process. This causes non-kosher ta’am of gevinas akum to pass into the whey. The kashrus agency must therefore continuously monitor the vat temperatures to prevent such scenarios, in order to verify that the whey is kosher.
  3. The most common factor which renders whey non-kosher is the pasta filata technique, which entails the cooking of some types of Italian cheese curds (most often mozzarella and provolone) in a very hot bath of water, as the cheese curd is mixed and kneaded, thereby endowing it with an elastic texture, ideal for melting (think of pizza or lasagna). The water from this process (called cooker water), which has ta’am and even fat from the gevinas akum cheese curd that is cooked, mixed and kneaded in it, is wholly non-kosher – yet many cheese plants pipe back their cooker water to the whey system, as cooker water is basically compatible with whey, and it easily merges into whey. The kashrus agency needs to assure that cooker water is hard-piped to drain or is otherwise removed from the production plant in a manner that prevents it from being incorporated back into the whey.

Whey is a complex material, and whey kashrus is likewise quite complex and challenging. The OU is proud to certify numerous brands of whey and whey-fortified products, all possible due to the very tight kashrus systems and extremely careful monitoring of our professional hashgacha team.

by Rabbi Avrohom Gordimer, RC, Dairy