MONTREAL—Dripping in fat, a Schwartz's sandwich is not just a local favourite, but it's internationally renowned and many tourists can't leave the city without trying it.

Schwartz's produces a lot of meat and a lot of fat, nearly 1,000 litres of yellow grease weekly. That fat is valuable and in recent weeks thieves have begun to target the restaurant’s reservoirs.

The fat from all the meat processed by Schwartz's, along with the French fry oil, is collected and stored in tanks behind the restaurant.

“At one point, we used to have to pay to take it away and now it's the opposite, they pay us,” said Schwartz's manager Frank Silva.

The fat is being used to make biodiesel, used to fuel everything from city busses to airplanes.

“I thought it was ridiculous I mean somebody actually stealing our oil, but obviously it's not,” said Silva.

The biodiesel market is hot and companies like Montreal’s Sanimax pay up to $800 per tonne of yellow grease.

“That’s a lot of money compared to what it was worth four or five years ago. It was like $300 for the same commodity,” explained Sanimax’s Thierry Finn.

As a result, many smaller restaurants have also had their grease stolen. So much so that Sanimax is now providing better security systems for their clients oil tanks.

“It's a new crime,” said Finn. “Businesses have attracted thieves and they're stealing more because they can find a buyer for it.”

Back at Schwartz's, most clients are upset to hear of anyone stealing from such a venerable Montreal landmark.

For its part, Montreal's famous smoked meat joint is now working with police to find out just who’s stealing their fat.