Back to top

(773) 465-3900


EZcRc Login

[email protected]



By Rabbi Dovid Cohen, Administrative Rabbinic Coordinator

Q. What is lactose? Is it dairy? 

A. Milk contains fat, two kinds of protein (casein and whey), water, calcium, and a type of sugar which is called lactose.  To create cheese, you add rennet or an acid (such as vinegar) to the milk, and it causes the casein and fat to clump together into “cheese”, leaving behind a grayish liquid that contains water, whey, calcium, and lactose.  That liquid can be filtered to isolate the whey, which will be dried into a powder and sold as “whey protein”.  The fluid left after that filtration step contains lactose, and if the water is removed from it, you will be left with plain lactose.

The most obvious thing about lactose is that it comes from milk and is, therefore, milchig.  [Lactic acid has a similar sounding name, but it is not made from milk, and it is pareve.]  However, to the surprise of most people, the halacha is that since it takes two separations to isolate it from milk, it is only milchig mid’rabannan.  [Poskim refer to it as meimei chalav.]  This is not just an academic point, and it has a very practical application.  It is forbidden to have benefit/hana’ah from milk and meat which are cooked together, but that issur only applies if the mixture is considered basar b’chalav mid’oraisah.  In this case, since lactose is only dairy mid’rabannan, one may have benefit from a food that contains meat and lactose (with no other dairy).  A common example of the issur hana’ah relates to pet food; if it contains meat and milk then it cannot be used, since the person is benefitting from it when he feeds it to his pet, but if the only dairy is lactose, then it may be given to the pet.  [Another example of basar b’chalav which is only assur mid’rabannan is when the “meat” is actually poultry; poultry cooked with milk is only assur mid’rabannan, and it would be permitted to have hana’ah from the mixture.]

We have seen that lactose is a byproduct of cheesemaking, and in order for cheese to be kosher a Jew must be present (and potentially participate) when it is made.  Cheese made without a Jew present is called “gevinas akum” and is not kosher.  In most cases, the whey and lactose separated from gevinas akum remains kosher.  It is beyond the scope of this article to explain why that is true, but it is generally accepted that if the milk was hot during the cheesemaking process, the whey and lactose become forbidden, since they absorbed ta’am/taste of gevinas akum.  That is not very common, but one of the reasons lactose requires hashgachah is to ensure that it was not created from this type of cheese.

Lactose is often found in chewable and swallowable tablets, and these items typically are not kosher-certified.  That raises questions for consumers who are ill and want to use the medicine.  Must they be concerned that the lactose is not kosher?  What if they only eat chalav Yisroel?  [See Koveitz Teshuvos 1:73a.]  Can they consume the tablet if they ate a meat meal less than 6 hours ago?  These are all questions that should be addressed to the person’s local Rabbi who can weigh the halacha/kashrus concerns together with the needs and leniencies appropriate for the person’s particular medical condition.

This article first appeared in the Let’s Talk Kashrus column, Yated Ne’eman, December 15, 2023.