While cheeseburgers — made with dairy cheese and beef burgers — are unlikely to appear on kosher restaurant menus anytime soon, a relatively lenient ruling issued by Ashkenazi Chief Rabbi David Lau has found that cultured meat could, in theory, be mixed with dairy.

Still, Lau’s ruling came with a significant caveat that would undermine the marketing strategies of the companies manufacturing lab-cultured meat: The burgers cannot be called meat, and cannot be made to look like meat or smell like meat.

The advent in the past decade or so of cultured meat, meaning meat grown in a lab rather than on a farm, has given rise to a number of questions for rabbis to answer — chiefly, can it be kosher and would it be considered meat as far as Jewish law, or halacha, was concerned. Over the years, a number of halachic authorities have weighed in one way or another.

Lau determined that the cultured meat produced by Aleph Farms, though not necessarily all cultured meat, is kosher and is “pareve,” designating a food that is neither meat (sometimes referred to as fleishig) nor dairy (milchig), such as vegetables or fish.

Culturing meat from fertilized embryos, instead of animal flesh, solves a number of halachic problems, allowing them to be considered pareve, according to Lau. For one, embryos are not considered to be part of the mother, but are a separate entity, meaning that using them does not run afoul of the biblical prohibition against eating flesh taken from a living animal.

According to Lau, embryonic stem cells are also not considered “meat” in Jewish law, as they are not really seen as food at all.

However — and this is a big caveat — while the product may not technically be considered meat, there is a concept in Jewish law known as marit ayin, which forbids actions that appear to be prohibited even if they are in fact permitted. Eating what looks like a standard beef burger with dairy cheese would clearly appear to be a prohibited action.

Another consideration is a prohibition against performing actions that could accidentally lead someone to doing something forbidden out of habit. A person used to putting cheese on cultured meat could then start putting it on regular meat too — or so the thought goes.

Lau deals with both of these in his responsum, and they lead him to rule that the technical status of cultured meat as “pareve” could be overshadowed by some real-world conditions.

For decades, meat substitutes and alternatives have become commonplace around the world, meaning there is less of a chance that a person seeing someone eating what appears to be a non-kosher cheeseburger would immediately jump to the conclusion that they were committing a sin.

In light of these two concerns — that treating cultured meat as “pareve” could lead to marit ayin and that it could lead to a “prohibited habit” — Lau ruled that if cultured meat is marketed as real meat rather than a meat alternative, and is prepared and packaged to look and smell like meat, then it should not be considered “pareve” and cannot be eaten with dairy products.

This indeed appears to be the case with Aleph Farms, whose primary products are cultured steaks that it says “deliver the same delicious taste, nutrition and sensory experience as the very best conventional steaks.”

In addition, Lau said that cultured meat should not be “marketed along with dairy products” as this could lead consumers to “take the mixing of meat and milk leniently and to disregard the prohibition.”

Finally, Lau stressed that this all applies only to Aleph Farms products, so long as they continue to be produced in the same way, and not to all cultured meat, which could use different techniques or ingredients.

So kosher cheeseburgers with cultured beef are still out of the question. For now, at least, kosher bacon burgers are out too