When we drink a glass of milk, we rarely realize that it consists of many components that have varying characteristics. These components are often separated and serve specialized functions in the manufacture of foods.

For example, the typical infant formula's ingredient panel reads: "Ingredients:...whey powder...sodium caseinate..." Countless foods that we consume every day contain whey and sodium caseinate (or some other "caseinate"-sounding material). What are these mysterious ingredients?

Casein is the protein found in milk, and it can be modified into caseinate, as will be discussed below. Whey is a by-product of cheese-making and casein production. Let's explore these substances and their kashrus.

Casein

Casein is a fat-free, pure protein found in milk that is useful in numerous food and non-food applications. There are two methods of isolating casein from milk, resulting in two types of casein: acid casein and rennet casein.

Acid casein is produced by adding hydrochloric acid to milk, causing the milk's pH to drop (i.e. it becomes more acidic). When the pH reaches 4.6, the milk's casein protein separates out of it. Rennet casein is made by dosing milk with rennet, the enzyme used to manufacture hard cheese. Similar to cheese-making, rennet causes the milk's casein molecules to form a solid or semi-solid curd matrix.

In fact, casein manufacture is very much like cheese-making. Soft cheese (technically termed "acid-set cheese") is produced by acidifying milk with bacteria cultures, and hard cheese (referred to as "rennet-set cheese") is made by adding rennet (along with some other ingredients) to milk. Just like in cheese-making, the remaining liquid by-product of casein manufacture is called whey. The difference between cheese and casein is that cheese contains large quantities of fat and lactose, whereas casein is a pure protein.

After casein forms, it is dried into powder in equipment called spray towers or spray dryers. Spray towers convert liquid into powder by shooting the liquid out of tiny nozzles into a large (usually multi-story), hot chamber, where the tiny liquid drops "atomize" into powder as a result of the intense heat and pressure, spiraling to the bottom of the chamber like driven snow . Acid casein dries into a thin powder, whereas rennet casein dries into courser granules, as it is a rubbery, hard cheese-like product.

Acid casein is used to fortify baby formula, coffee creamers, health beverages, protein supplements and even pet food, and it is also utilized in paints and various other technical applications. Rennet casein is used primarily in imitation cheese, and it is also used in costume jewelry. (Casein is an amazingly firm protein that can withstand manipulation of all sorts. It is readily hardened into a gem-like texture, and it can be easily and deeply colored so as to bear the appearance of a jewel. It is this firmness and ability to withstand manipulation that makes casein ideal for so many technical applications, including use in construction materials, glues, paints, cosmetics and plastics.)

Acid casein cannot be used in its normal form because it does not dissolve into liquids. Therefore, it needs to be made into a soluble material in order to be able to dissolve into the product in which it is used. Alkali solutions are added to acid casein to make it soluble. When acid casein is mixed with an alkali solution, it is called caseinate. The type of alkali solution added to casein to make it soluble determines the finished caseinate product. When potassium is used, we get potassium caseinate; when sodium is used, we get sodium caseinate, and so forth.

Acid casein is far simpler (and cheaper) to make than rennet casein. Acid casein is made in many locations throughout the world, but its production is particularly prominent in Australia, New Zealand, Ireland, France, Germany, Denmark, Russia and former USSR nations, China and India. Rennet casein is commonly made in made a more limited list of countries, among which are Australia, New Zealand, France and Ireland.

Whey

Whey consists of water, salt, milk sugar (called lactose), some fat and residual protein. It is made of the portion of the milk that did not become cheese. Whey is often dried into powder for use as a somewhat nutritious filler in numerous products (butter, ice cream, cookies, etc.). Its fat can be removed and used as cream (called "whey cream"), and its protein content can be extracted, resulting in what is called "whey protein concentrate". Whey cream is similar to fresh cream (which is the fat skimmed off of milk, called "sweet cream"), although it is more salty and tangy, reflective of its cheese-making origins. Whey cream is ideal for use in ice cream (where the flavors and sweeteners mask whey cream's tangy taste), and butter is also often made from whey cream or a blend of whey cream and sweet cream. Whey protein concentrate - like caseinate - is ideal to fortify health products. Take a look at any dairy nutrition product, and you will surely see caseinate and/or whey protein concentrate among the ingredients.

Kashrus Issues

Casein
In the United States, there is a basic misconception about casein's status as a dairy ingredient. Casein is not generally manufactured in the US due to an absence of government subsidies for its production. In order to protect its farmers and plants, the American dairy lobby has succeeded in getting the US government to limit the appeal of casein, as it is viewed as a foreign threat to the American dairy industry. Thus, FDA regulations stipulate that casein needs to be listed on all food labels as a "non-dairy" ingredient. (That is why coffee creamer is technically - and strangely - required to be called "non-dairy" creamer.) The real purpose of this is to make consumers think that casein is an unnatural substance to be avoided. This labeling regulation is particularly confusing for kosher consumers, as some of them assume that "non-dairy" products containing casein - such as many coffee creamers and imitation cheeses - are really pareve. This is an obvious misconception, though, as casein is milk protein and is fully milchig.

As with any food, all ingredients and equipment used in casein production must be kosher. This is usually simple to achieve from the ingredient standpoint. Acid casein does not contain any problematic ingredients (milk and hydrochloric acid - that's it). As for rennet casein, the only really kosher-sensitive ingredient used is rennet, which can derive from calf stomach lining. An abundance of microbial (artificial) rennet sources are available, so this issue can be easily dealt with.

There is a major equipment concern, however. Casein is often spray-dried in spray towers shared with other products. Some drying facilities do what is called "toll drying", meaning that they dry material for anyone who sends it to them and is willing to pay. Some drying plants process non-kosher meat, cheese and wine powders, and who knows what else in the same spray towers. So, too, otherwise-kosher acid casein is sometimes dried in the same towers as non-kosher rennet casein (see below what makes most rennet casein non-kosher), this rendering the acid casein non-kosher as well. Kashrus agencies need to keep a tight watch to assure that drying equipment be dedicated kosher or that it be kashered properly for casein production.

When a spray tower needs to be kashered for casein production of any other purpose, it can be done in one of two ways. The dryer can be heated to above 450 F degrees to create a "libbun kal", a low-level scorching, that will be maintained for a specific (long) duration - perhaps a few hours - or it can be kashered via "hag'alah" - "purging". Many spray-dry companies are hesitant to allow libbun kal for fear that the intense heat will damage the equipment. Kashering with hag'alah is thus often the best approach, but it can be very complex, as the boiling hag'alah water must be shot through the entire chamber of the dryer at a high velocity so as to cover the full interior and remain boiling throughout. This is very difficult from an engineering perspective, and it takes nothing short of master mashgichim and expert plant technical staff to achieve it.

As far as actual production, casein has the same kashrus concerns as cheese. The Shulchan Aruch (Yoreh Deah 115:2) paskens that cheese made by a nochri is non-kosher; such cheese is termed 'gevinas akum'. Kosher cheese, called 'gevinas Yisroel', is the only cheese that may be consumed. The Remo (ibid.) writes that gevinas Yisroel is obtained when a Yisroel supervises the cheese making, whereas the Shach (ibid. s.k. 20) holds that the Yisroel must personally add the rennet to the milk in order to produce gevinas Yisroel; merely being present to supervise is not enough. Most poskim hold like the Remo and only require that a Yisroel be present for supervision; however, the Gra (ibid s.k. 14) and some other poskim write that the halacha follows the Shach. (In an upcoming article in the Mesorah journal, I attempt to demonstrate that many Rishonim also hold like the Shach.) The prevalent practice among most kashrus agencies is to follow both the Remo and the Shach, thus having a mashgiach present for cheese production and having him personally add the rennet to each vat. This can be done manually or by the mashgiach activating the rennet feeder, as is common in more modernized facilities.

Rennet casein is governed by the requirement of gevinas Yisroel, as its manufacture is categorized as that of hard cheese-making. However, poskim argue as to whether or not soft cheese is also subject to the requirement of gevinas Yisroel, and that same machlokes applies to acid casein as well, for it is in the halachic category of soft cheese. On a practical level, kashrus agencies typically treat acid casein as not subject to the din of gevinas Yisroel.

It should furthermore be noted that although rennet casein is on a kashrus par with hard cheese and is encumbered by the requirements of gevinas Yisroel, its kashrus supervision is often more taxing than supervising hard cheese. Whereas a non-kosher cheese company may have a mashgiach present for a day-long kosher production every week or month, kosher rennet casein campaigns are often scheduled to last for weeks straight, as rennet casein plants prefer to have longer, less frequent kosher productions in order to avoid frequent kashering of their spray towers. (Kashering requires that the towers be unused for 24 hours prior to kashering, and it necessitates immaculate pre-cleaning, usually far more thorough than the cleaning done between non-kosher products.) It is therefore not uncommon for a whole team of mashgichim to supervise a kosher rennet casein campaign for a 24/7 three-week production, breaking only for Shabbos.

Whey
As noted above, whey is a by-product of cheese and casein production. Whey therefore shares the same basic halachic concerns as cheese and casein, with one very major exception. Poskim rule that whey is not encumbered by the stricture of gevinas Yisroel, such that whey from gevinas akum can therefore in theory be considered kosher, even without on-site supervision (so long as the ingredients of the cheese or casein are kosher, of course). The concept is that when milk separates into curd (cheese or casein) and whey, Chazal only declared the curd to be prohibited if it is gevinas akum; the whey was never subject to that rule.

Despite this leniency regarding whey, its kosher certification is quite complex. The most unique aspects of this complexity relate to "hot-process" cheese - cheese that is made at high temperatures. Many poskim opine that the whey of such cheese is non-kosher when the cheese is gevinas akum, as the non-kosher cheese curd transfers its non-kosher taste to the whey while they are together in the vat at high temperatures. Thus, Swiss and Parmesan cheese whey is usually not kosher according to this approach, as the heat used to make these cheeses passes their non-kosher status to the whey in the vat. On the other hand, barring any additional kashrus concerns, cheddar and mozzarella whey poses no temperature issues, as these cheeses are not made at high temperatures.

Some cheeses are cooked in a hot bath called a "cooker" after they are removed from the vat. This endows the cheese with an elastic texture that will enable it to melt and not run; mozzarella cheese is cooked, as it needs to melt onto pizza and not run off the dough. Many cheese factories salvage the used water from their cookers, as this water accumulates large amounts of fat and protein from the cheese that is cooked therein. After removing the cooker water's fat and sometimes its protein, these plants tend to add the water into their whey, as cooker water and whey are very compatible. Cooker water is non-kosher due to its hot absorption of taste (and often particles) from non-kosher cheese cooked in it; cooker water renders any whey which contains it non-kosher as well.

Casein and whey are consumed by nearly everyone; who would ever think that their kashrus is so complex?