(NEXSTAR) – Steak ‘n Shake, a burger chain primarily located in the Midwest, announced last month that all of its restaurants would cook their french fries using beef tallow, claiming this method results in the “best” product possible.

In doing so, the company effectively made its french fries unsuitable for vegetarians, a group Steak ‘n Shake apparently doesn’t mind alienating.

“Vegetarians should eat fries elsewhere,” Dan Edwards, the COO of Steak ‘n Shake, wrote in an email to Nexstar. “At Steak n Shake we want to offer the best. In doing so, we can’t make all people happy. We just need to please the ones seeking fries made in an authentic way.”

Whether or not cooking fries in beef tallow is truly “authentic” (some of the earliest recipes called for duck fat or butter), it is true that many popular fast-food chains — McDonald’s, Burger King, Wendy’s — had used beef tallow to fry their potato products before 1990, The New York Times reported at the time.

Today, the nutrition webpages for Burger King and Wendy’s list no animal-derived ingredients in their french fries. (Both restaurants acknowledge that their fries are cooked in the same oil as other meat or fish products.) McDonald’s fries, however, are made with a flavoring that includes hydrolyzed milk — a non-vegan ingredient.

But here’s where things get murkier: The hydrolyzed milk is listed as a component of “natural beef flavor,” which is used in the initial batches of frying oil. But it’s unclear what else the “natural beef flavor” contains because the Food and Drug Administration does not currently require that food manufacturers declare every component of a “natural” flavor. (McDonald’s is, nevertheless, required to disclose the hydrolyzed milk component of the flavoring, as milk is a common allergen.)

It’s possible, though, that natural beef flavoring might not contain any actual beef. “Natural” flavors must simply be made with flavoring components derived from natural sources and not necessarily the food most associated with that flavor, per the FDA. (Vanilla flavoring can be derived from clove or straw, for instance.) That said, beef flavoring is sometimes made using amino acids found in beef, Nexstar’s KTLA once reported.

A rep for McDonald’s did not return multiple requests for more information on its natural beef flavoring, nor on whether the company considers its fries — which are not suitable for strict vegans — to be vegetarian-friendly.

Vegans and vegetarians, meanwhile, might have better luck across the pond: Fries served at UK locations contain fewer ambiguous ingredients and are indeed considered vegan-friendly, according to McDonald’s UK.

“The fries are not coated in any fats or substances from an animal,” reads an FAQ webpage for McDonald’s UK. “Once at the restaurant, our fries are simply cooked in dedicated frying vats in a non-hydrogenated blend of sunflower and rapeseed oil which is 100 percent suitable for vegans.”