I arrive at the pizza parlor in San Francisco’s Tenderloin with the “kashrut experts” waiting for me inside. I’m at Supremo Pizzeria with Nathaniel Weiner and Zvi Septimus for two reasons.

One: This tiny place with just three red-vinyl booths advertises its pizza as both “halal” and “kosher” — even though the menu lists toppings such as pepperoni, salami, sausage, Canadian bacon and grilled chicken.

Two: San Francisco residents Zvi and Nathaniel grew up Orthodox in New York but don’t keep kosher anymore, making them ideal dining companions for a conversation about kashrut.

Halal, the Islamic dietary law often compared to kashrut, has no prohibition against mixing milk and meat. But it does prohibit pork, and so Supremo’s meat products all are made from halal-certified turkey and beef.

What makes the restaurant decidedly not kosher is putting those meats on top of cheese. Plus, those meats aren’t actually kosher to start with, and everything is prepared in a non-kashered kitchen.

When a j. reader alerted us to Supremo’s “false” kosher claim on its delivery menu, I started my research on halal vs. kosher. Rabbi Andy Shapiro Katz, an observant Jew and assistant head of school at Jewish Community High School of the Bay, drove home the point that kashrut is more restrictive.

“I have never heard of a Jew treating halal meat as a substitute for kosher,” he said. But “many Muslims do eat kosher meat and consider it halal.”

I went to Supremo intending to do the mouthwork — er, legwork — on a news article about Jewish and Islamic dietary traditions.

But once I sat down with Zvi and Nathaniel, I was struck by how pizza had become deeply meaningful to them over their lifetime. They grew up in an Orthodox neighborhood in Cedar-hurst, N.Y., and have been close friends since age 3. And anytime they have lived in the same city, they have gathered for pre-Shabbat pizza.

“This place doesn’t have tehina — that’s how you know it’s not kosher,” Nathaniel jokes. His hometown favorite, Sabra Kosher Pizza, serves customers a side of tehina if they want it.

The pizza arrives at our booth. Zvi and Nathaniel have ordered plain cheese pizza, but it has nothing to do with keeping kosher; it’s pizza in its purest form, they say. The men conduct the “sag test,” a barometer of the dough’s texture. They argue about deep dish versus thin crust. They blame the minerals in the local water supply for all the poor pizza in the Bay Area, saying the only acceptable pies in San Francisco are from Pizza Orgasmica, Arinell and Marcello’s.

“We take this really seriously,” Nathaniel says.

Adel Hamed, the owner of Supremo, says he gets many confused customers. He’s not trying to deceive. It turns out the former owner used kosher to mean “Islamic kosher” because it is a more recognizable a term than halal, he said.

Hamed is planning to print new menus making it clear Supremo serves halal-certified meats, not kosher.

“I know the Jewish certification has different rules,” he says. “Jews assume this word, kosher, means that it was certified by a rabbi. It confuses the Jewish community. I have had to explain this to many people.”

Zvi is currently studying Talmud in a doctoral program at U.C. Berkeley. Though he does not keep kosher anymore, he maintains a kosher kitchen so friends and relatives feel comfortable eating in his home.

He explains that the kashrut certification and supervision process is an invention of contemporary 20th century American life. “With the creation of the [kashrut] industry came stringency,” he says. “The more sectarian we’ve become, the less trust we have.”

Long ago, before Star-K and OU Kosher and Kof-K, Jews relied on a person’s word that food was kosher. His grandmother, for instance, kept kosher on the Lower East Side for decades without the aide of that little kosher symbol.

Even today, we don’t need a Star-K to know that Supremo pizza isn’t kosher. And yet a few slices can still bring people together on a Friday afternoon.

Stacey Palevsky lives in San Francisco. She can be reached at [email protected]