Culture For The Masses: The Complexities of Kosher Yogurt Certification

Yogurt was first produced thousands of years ago. Dairy history and legend indicate that yogurt originated in Iran or Turkey. One story has it that an ancient Turk was carrying milk in his goatskin for some time, when he noticed that the substance had developed into a thick, creamy mass. This new product was referred to as yogurt.

In 1900, a Russian biologist named Dr. Ilya Metchnikoff, of the Pasteur Institute in Paris, was able to isolate bacillus cultures for yogurt production, marking the beginning of modern yogurt manufacture.

Dr. Metchnikoff demonstrated that yogurt’s bacteria fought dangerous germ bodies in the colons of mammals, and he theorized the positive effects of yogurt bacteria cultures on humans. Shortly thereafter, yogurt became a staple in the American diet, and the OU been has privileged to certify many brands for millions of kosher consumers in the United States and abroad.

Why is yogurt so popular that the general market and kosher consumer base have made yogurt one of the fastest growing dairy products throughout the world? There are two answers to this question: A) taste, and B) health benefits.

Yogurt is an ultra-pliable food which can be manipulated, filled, thickened and flavored in countless ways. Unlike most dairy products, yogurt has virtually no bounds. When one considers the multitude of flavors, fruit and confectionery fillings, thickeners and sweeteners used in the many varieties of yogurt available to us, it is clear that there are thousands of possibilities. (Ever heard of cheese with fruit filling, banana-flavored butter, sour cream with chocolate chips…? You get the picture.)

The health benefits of yogurt are quite unique. Its bacteria cultures (to be noted later in this article) assist in the digestive and gastrointestinal tracts, and they enhance overall immunity by attacking disease-promoting bodies throughout the body’s food trail. It is even suspected that some infections and pre-tumorous conditions may be killed by yogurt’s live bacteria.

Of all dairy products, kosher yogurt is among the most complex in terms of its kosher requirements and proper supervision. To put it more precisely, if you take the kosher considerations of soft cheese and combine them with the kosher issues of ice cream, you come out with a basic framework for kosher yogurt.


All yogurt begins with milk. The milk’s fat ratio may be adjusted by adding cream or non-fat dry milk.

Afterwards, sugar or artificial sweetener may be incorporated, and stabilizers — which create the desired consistency — are then fed into the yogurt mix.

The mix is usually then pasteurized, subsequent to which it is dosed with acid-based dairy cultures (most commonly lactobacillus bulgaricus and streptococcus ther-mophilus), after which the cultured mass is left to incubate for a specific amount of time in closed yogurt vats.

Following incubation, fruit filling, flavors and even colorants may be added. The product is then filled into cups or tubs and is ready to go. (It is important to note that the only hot phase is pasteurization. The rest of the process is cold, ambient or warm.)

This seems pretty straightforward. Why, then, did we make certification of yogurt out to be so complex?

Let’s go through some of the above steps again more carefully by category, from the perspective of a kosher certifier.


Milk is milk. No kosher problems here (unless we are dealing with yogurt in lands which consume non-kosher varieties such as camel or pig milk or have inadequate milk regulations…)

Cultures, however, are another story. Most dairy cultures are grown in labs which handle kosher and non-kosher materials beyond the imagination. Some cultures are grown on surfaces which are non-kosher, and some are nourished with non-kosher nutrients. Shared culture equipment is another common issue. Cultures are kosher only when their environments and nourishments are fully kosher. Thus, we are working with pretty sensitive stuff.

Cream and non-fat dry milk, used to adjust yogurt fat ratios, are also kosher-sensitive. Cream can derive from non-kosher whey, called “whey cream,” and it often shares equipment used for non-kosher whey cream manufacture. Non-fat dry milk can be dried in spray towers also used for drying non-kosher meats, cheese, etc. Proper kosher supervision is most certainly necessary!

When we get to stabilizers, we approach the most hazardous area of yogurt certification. The recent trend in the industry has been to increase the thickness of product, creating a “Swiss-style” consistency. The most common stabilizer to achieve this result is gelatin, most of which comes from the bones and hides of non-kosher animals. It is for this reason that many varieties of yogurt bear no kosher symbol or feature just a generic “K”, as the OU cannot certify them due to the presence of non-kosher gelatin. (It is noteworthy that the OU does certify kosher gelatin, manufactured by Norland Industries and Glatech Productions. Kosher marshmallows utilize these gelatin sources, and they are now available for the dairy industry as well.) Other non-kosher stabilizers contain a mix of gelatin and non-animal based substances.

Stabilizers present in OU-certified yogurt are starch or gum based. These stabilizers need proper kosher certification, as they can be processed on non-kosher equipment and can even contain trace amounts of gelatin.

Fruit fillings, flavors and colorants may be non-kosher. Kosher status must obviously be verified.


The first thing that the OU needs to do when we certify a yogurt plant is to clear all ingredients as kosher.The next task is to determine if the plant also makes non-kosher product and — if so — evaluate whether or not the plant can handle an OU program in light of its non-kosher production.

There are four categories of non-kosher issues: (1) pasteurization, (2) post-pasteurization, (3) formulas and (4) kosherization.

  1. PASTEURIZATION: Every material which is pasteurized is — of course — exposed to hot equipment. Non-kosher ingredients which are run through the pasteurizer can render it non-kosher. Although the OU does not permit the use of kosher and non-kosher identical ingredients in the same plant (such as kosher and non-kosher cream, non-fat dry milk, etc.), we need to see if gelatin or gelatin-based stabilizers are used. If so, they can render the pasteurizer and related equipment non-kosher, requiring kosherization after each non-kosher campaign.
  2. POST-PASTEURIZATION: Once we have assured that the pasteurization system is kosher for kosher-certified production, we need to see if there are non-kosher ramifications of non-kosher yogurt later on in the manufacturing process. Gelatin-based yogurt — as well as yogurt with non-kosher fruit fillings, colors or flavors — often shares the same incubation or storage tanks and fillers as kosher yogurt. This equipment must be reliably cleansed before it is used for kosher product, and tanks cannot hold kosher and nonkosher product for 24 hours or more. The OU assures that this is the case.
  3. FORMULAS: When a plant processes a non-kosher product (or any other product, in general), the OU must carefully review formulas to verify that kosher yogurt utilizes only kosher ingredients. The more nonkosher production at a given plant, the more time and work will be required for the rabbinic field representative (RFR) to go through the books or computer records for formula review.
  4. KOSHERIZATION: As noted above, non-kosher yogurt run-through a pasteurization system can require kosherizaton after it is processed. In this case, the rabbinic coordinator and RFR work out a system by which the plant’s CIP routine meets kosherization specifications. The RFR reviews Taylor charts generated by the CIP to assure that necessary temperatures are reached, and he verifies production and CIP sequencing upon each visit as well.

Certification of kosher yogurt poses the issues of stabilizers and cultures related to soft cheese, alongside dealing with the many additives and flavors encountered when certifying ice cream. Complex…but delicious.

OU Kosher Staff