It’s More Than Curds and Whey: OU KOSHER’s Dairy Expert Tells How To Kosherize A Cheese Company

Some time ago, I received the following letter:

As you know, I manage a cheese company, which manufactures kosher and non-kosher cheese, plus kosher whey powder. You are familiar with our equipment and how it needs to be kosherized, but my staff needs some education on this. Can you please explain the kosherization rules for the equipment so that I can share them with my staff? If you don’t mind, I would also appreciate if you could include a basic review of how the equipment works, so that new employees can also benefit from this.

Cheese Equipment:

Plate Heat Exchanger


When cheese is manufactured, the milk must usually first be pasteurized (heat-treated to destroy harmful bacteria); this is typically done in a plate heat exchanger, in which the milk travels along metal plates with increasing intensities of heat. Once the milk reaches the desired temperature (usually 161° F), it is held for a required duration at that temperature and is then cooled, passing along metal plates with increasing intensities of coldness. For the sake of efficiency, incoming cold milk is heated by outgoing hot milk, before the outgoing hot milk is cooled down; the hot and cold milk pass along different sides of the same plates, such that the outgoing hot milk passes its heat to the incoming cold milk, through the metal of the plates.

This system does not itself heat or cool the milk sufficiently, and plate heat exchangers therefore need heating and cooling sections to fully perform the heating and cooling processes. The heating section of plate heat exchangers consists of extremely hot water on one side of plates; when milk travels over the other side of these plates, it becomes very hot. So too, cooling is accomplished though chilled water which is held on one side of the plates on which pasteurized, hot milk passes, so that this milk is chilled in the process.

The plate heat exchanger is among the most complicated equipment for the purposes of kosherization. Although dairy factories sanitize plate heat exchangers at least once per day, such sanitization (“CIP” – “cleaning in place”) usually does not constitute a kosherization for a variety of reasons – among them the fact the standard CIP is usually performed at 165-185 degrees, which is inadequate for kosherization, as well as the fact that CIP protocol often does not include certain areas of equipment that kosher law requires to be kosherized. Normal CIP also frequently features hot acid and caustic solutions followed by ambient water for cleaning, and some kosher law authorities do not accept kosherization with anything other than water.

To properly kosherize a plate heat exchanger, one must take the following steps:

• Assure that the equipment is totally fallow for 24 hours, or – according to some opinions in kosher regulations – embitter the equipment via an embittering solution, run at close-to-boiling temperatures through all areas which has hot product contact.

• Flow boiling water through the above areas.

This doesn’t sound too complicated; it seems to be kind of like a good sanitizing. However, it is anything but simple. Here is why, followed by what needs to be done to address some unexpected complexities:

• The heat exchanger’s regeneration (or “regen”) areas, where hot product heats cold product and vice versa through metal plates, are often not able to be easily kosherized with boiling water. Typical CIP often cannot reach such temperatures in the regen areas. The OU rabbinic field representative (RFR) and rabbinic coordinator (RC) must work carefully with the plant’s engineers to accomplish this feat.

• Similarly, the heat exchanger’s cooling section is often hard to kosherize. To do so, the cooling mechanism must be off, and the flow of kosherization water may need to be diverted from its normal course in order to reach the cooling section while the water is yet boiling.

• Before production, the heat exchanger’s balance tank, where cool product is metered into the heat exchanger, often has exposure to hot product. This is because part of the start-up of a heat exchanger involves recirculating hot product back to the balance tank until the heating areas of the heat exchanger are hot enough to pasteurize.

Boiling water run through the heat exchanger usually drops below boiling temperatures by the time it arrives back at the balance tank. Thus, boiling water must be specially diverted back to the balance tank by changing its normal course, in order to kosherize the balance tank properly. Again, this needs the involvement of the plant’s engineers in order to be done correctly.

• The water that passes heat to product through metal plates can have absorption of dairy or non-kosher product via seepage or via taste transfer through the metal plates. Thus, the heating water in these plates can be non-kosher or have a dairy status. The solution is to evacuate and dispose of the heating water (which is otherwise not changed and is used over and over again for months) before kosher-dairy or non-dairy (“pareve”) productions and to refill the plates’ heating water area with fresh, unused heating water — or to embitter the old heating water so that it cannot pass taste back to the new product.

An RFR must carefully monitor this all; there is no automated recording of these details in most plants. (It is also critical that the heat exchanger’s plates be periodically opened and cleaned in the presence of an RFR, as these plates can accumulate build-up of product, which may be a serious kosher issue.)

Cheese Vat:


After milk exits the heat exchanger, it enters a vat. This vat is normally made of steel and has jackets on it; these jackets hold hot water and are set to specific temperatures for cheese production. (Every cheese has its own production temperature.) When turned on, the jackets heat the vat in which the cheese is made.

The milk in the cheese vat is dosed with acid cultures (or direct acid, as in the case of a few soft, rennetless cheese varieties), and rennet is added as well. Cream (milk fat) and non-fat dry milk may also be added to regulate fat ratios, and vinegar may be added to regulate pH.


Unlike heat exchangers, cheese vats are usually not too complicated in terms of kosher protocol. The reason is that most cheeses (such as cheddar, mozzarella, Edam, Muenster, and Gouda), when made non-kosher, are not “hot vat” cheeses; these cheeses are coagulated at temperatures which are not high enough according to kosher law to render a vat non-kosher, and their vats thus do not need kosherization prior to kosher cheese production. A good washing, followed by inspection by an RFR, is all that is needed.

Vats used for hot-vat cheeses, such as most Parmesan and Swiss Emmenthaler, require kosherization before use for hot-vat kosher cheeses. In this case, the vats need to be cleaned, left fallow for 24 hours, and then totally rinsed with boiling water, with the jackets providing as much of the heat as possible. (In some cases of great need, embitterment, discussed above, may be done, if 24 hours of down-time is not feasible.)

Rennetless cheeses, referred to as acid-set cheeses (such as cottage cheese, cream cheese and farmer cheese) are normally made at very high temperatures, and their vats or kettles need full kosherization. (The cheeses discussed above, which use rennet to coagulate them, are termed rennet-set cheeses.)

Of critical import: After their removal from the cheese vat and formation, mozzarella and provolone cheeses are cooked in special cheese cookers, where they are stretched and manipulated in order to endow them with an elastic texture. These cheese cookers operate at 165-180° F and need full kosherization before kosher use.

Curd and Whey Separation:


Once the milk turns into curd (cheese) and whey (the part of the milk that did not become cheese, and remains pure liquid), it is evacuated from the vat and separated, usually via a draining and matting conveyor (“ DMC”); the curd flows to one area and the whey drips down to dedicated vessels.


The equipment used for separating curd from whey does not have any heat applied. Thus, the curd and whey temperature at this point is always the same or lower than the curd and whey temperature in the vat, and the same kosherization or mere cleansing requirements of the vat surely pertain here.

Salting and Molding Equipment:


The curd is then left to dry and is subsequently molded into cheese and salted; salting preserves the cheese from becoming quickly rancid. This salting may be performed on special salting tables, or by immersing the curd in brine (a solution of very salty water) for a long time – a day or more in many cases. This brining occurs in a series of brine tanks, in which the cheese is submerged in brine as per the relevant specifications.


According to most kosher certification professionals, modern cheese tables and molding equipment normally require mere cleansing (not kosherization) under the supervision of an RFR, before commencing kosher cheese production. Although cheese molding equipment as discussed by kosher law authorities hundreds of years ago required real kosherization, modern cheese tables and molding equipment normally do not. (Today, there is less salt used, the equipment has no crevices, and the cheese contacts it for shorter durations. Nevertheless, some kosher law authorities do require kosherization of modern salting tables, maintaining that the basic rationale necessitating this still pertains.)

However, brine tanks are another story. Since these tanks often hold cheese upwards of 24 hours and the same brine in them is reused over and over for months for non-kosher cheeses, it is absolutely required that new brine be used for kosher manufacture and that the tanks be lined or kosherized. (Kosherization is often not feasible, as brine tanks can be made from fiberglass, which cannot be kosherized). Cheese companies are hesitant to dispose of old brine, rich with flavor from non-kosher cheese absorption; so too are companies at times not happy to line or kosherize their brine tanks. Nevertheless, there is no other way to use brine and brine tanks for kosher cheese manufacture.

Cutting and Packaging:


The cheese is then cut into desired size, packaged and labeled.


Cheese cutting and packaging equipment is the easiest to deal with from a kosher perspective. This equipment does not use heat, and kosherization is therefore not necessary.

There are two ways to handle cutting blades: Have them scrubbed with abrasive material and then inspected by the RFR for cleanliness and lack of residue; or, save time and use new blades. The truth is that cheese cutting blades are replaced pretty often, and most companies will readily use new blades for kosher production.

Packaging equipment needs to be inspected by the RFR for cleanliness and is then ready for use.

Whey Production and Equipment:


We explained above that whey is drained from cheese after removal from the vat. Some small cheese companies dispose of their whey or sell it to farms to be mixed into animal feed. (Whey contains protein and is a good addition to animal feed.) Other cheese companies dry their whey into powder in spray dryers. This equipment consists of one to three chambers, in which liquid (whey, in this case) enters at the top (or the side, for certain types of dryers) and is ultra-heated by a flame or heating element.

The liquid is quickly atomized, or made into powder, at which point it passes through the dryer as tiny particles, to be collected for bagging at the exit of the chamber – or to enter another chamber or two for further removal of moisture. Although our case deals with whey, spray dryers are used for the manufacture of non-fat milk powder as well as for most food powders.


How does one kosherize a spray dryer? One would think that spray dryers could be kosherized like ovens – turn on the heat full- blast and achieve a scorching effect, if and once the requisite temperature is attained. However, it is not so simple, as spray dryers are open vessels through which air passes, and the spray dryers’ metal walls cannot therefore become hot enough to kosherize via a scorching effect. Yes, the internal air temperature may become very high, but the metal walls never do.

Therefore, spray dryers must be kosherized via hot water purging. After being left fallow for 24 hours and checked for cleanliness, boiling water is run through the nozzles of the spray dryer, so as to kosherize the nozzles. Then, a series of spray balls, which are like ultra-high volume shower heads, must be lowered into the dryer’s chambers; these spray balls shoot boiling water all over the entire internal walls of the dryer. The RFR must verify that there are enough spray balls and that they emit sufficient volumes of water to coat the whole interior of the dryer, so that every single spot is covered by a cascade of hot water.

The RFR then makes sure that the exiting water, at the end of the chamber, is boiling. This is because it is easy to shoot boiiling water through the spray balls, but the water often cools down as it travels through the chamber. Thus, verifying that the water upon exit is indeed boiling enables one to know that the water was boiling when it was in the chamber of the spray dryer as well, at every single spot.

Rabbi Andrew Gordimer is an OU Kosher rabbinic coordinator and group leader at OU headquarters. He specializes in the dairy industry and is responsible for administering the OU Kosher programs of over 80 client companies. He is a frequent contributor on topics of kosher law and other topics to various publications including BTUS. His most recent article, “Greek Yogurt for the Cultured Among Us,” appeared in the Summer 2010 issue.

Rabbi Avrohom Gordimer
Rabbi Avrohom Gordimer is a rabbinic coordinator at OU Kosher, where he specializes in the dairy industry. Rabbi Gordimer is the chairman of the OU Dairy Committee, and he manages the OU programs of over 90 certified dairy companies.