Order a bowl of turkey chili at a St. Louis-area Panera Bread cafe and it’ll cost you a penny. Or $5. Or $100. In other words, whatever you decide.

Three years after launching the first of five pay-what-you-want cafes, the suburban St. Louis-based chain on Wednesday quietly began its latest charitable venture that takes the concept on a trial run to all 48 cafes in the St. Louis region.

The new idea experiments with a single menu item, Turkey Chili in a Bread Bowl, available at each St. Louis-area store for whatever the customer chooses to pay. The new chili uses all-natural, antibiotic-free turkey mixed with vegetables and beans in a sourdough bread bowl. The suggested $5.89 price (tax included) is only a guideline. All other menu items are sold for the posted price.

Panera calls it the Meal of Shared Responsibility, and says the potential benefit is twofold: Above-the-cost proceeds go to cover meals for customers who cannot pay the full amount and to St. Louis-area hunger initiatives; and for those in need, the 850-calorie meal provides nearly a day’s worth of nutrition at whatever price they can afford.

“We hope the suggested donations offset those who say they only have three bucks in their pocket or leave nothing,” said Ron Shaich, founder, chairman and co-CEO of the chain and president of its charitable arm, Panera Bread Foundation.

If the experiment works in St. Louis, it could be expanded to some or all of the chain’s 1,600 bakery-cafes across the country, though Shaich said there is no guarantee and no timetable for a decision.

Panera has long been involved in anti-hunger efforts, starting with its Operation Dough-Nation program that has donated tens of millions of dollars in unsold baked goods.

The first pay-what-you-want Panera Cares cafe opened in the St. Louis suburb of Clayton in 2010. Others followed in Dearborn, Mich., Portland, Ore., Chicago and Boston.

At those nonprofit cafes, every menu item is paid for by donations. Kate Antonacci of Panera Bread Foundation said roughly 60 percent of customers pay the suggested retail price. The rest are about evenly split between those who pay more and those who pay less.

The Panera Cares cafes generally bring in 70 to 80 percent of what the traditional format stores do, Antonacci said. That’s still enough for a profit, and Panera uses proceeds for a job training program run through the cafes.

The new idea is fairly low-profile. Shaich said Panera is relying on media reports and word of mouth — no direct marketing, no advertising. Signs in the St. Louis cafes will tout the idea, and hosts and hostesses will explain it to customers.