More than two dozen bar and restaurant owners across New Jersey may have used cheap booze poured from top-shelf bottles to overcharge customers, the state Attorney General's Office announced Wednesday.

Though none of the proprietors have been charged, details of the investigation - dubbed "Operation Swill" - will be released at a news conference Thursday.

In the meantime, officials issued a statement that identified 29 licensed bars and restaurants they said were under investigation, allegedly charging customers for premium drinks made with cheap liquor camouflaged as high-end brands.

On Wednesday morning, officials of the New Jersey Division of Alcoholic Beverage Control, with the assistance of the Division of Criminal Justice, raided the businesses and seized inventory, the news release said. The yearlong investigation involved 100 state officers.

"Specifically, the . . . investigation indicates that these 29 establishments were allegedly engaging in a practice of filling premium-brand bottles with nonpremium brands in an effort to fool the customer and increase their profits," the release said.

"The customer paid for the premium brand, but was instead, unbeknownst to the customer, poured the nonpremium brand."

The investigation began with customer complaints and used confidential informants and new technology to field-test samples taken covertly by detectives.

Among area businesses that authorities say they raided Wednesday are Sunset Tavern in Burlington; Graziano's Ristorante in Chesilhurst; Villari's Lakeside in Gloucester Township; and Italian Affair in Glassboro.

Giuseppe Celano, owner of Italian Affair, declined to comment, as did a woman who answered the phone at Villari's Lakeside. A female employee at Graziano's Ristorante said no manager was available. A male employee at Sunset Tavern said no one was immediately available to speak about the allegations.

Authorities said they also raided Railroad Cafe, East Rutherford; Brick House, Wyckoff; Yesterday's, Marmora; Bells Tavern, Lambertville; Brunswick Grove, East Brunswick; Murray's, Dover; Sona Thirteen, Morristown; Blackthorn Restaurant, Parsippany; Ruby Tuesday, Bridgewater; Cafe 34, Matawan; Applebee's, Kearny; and Cucina Calandara, Fairfield.

Also raided Wednesday were TGI Fridays restaurants in West Orange, East Windsor, Old Bridge, North Brunswick, Piscataway, Freehold, Marlboro, Hazlet, East Hanover, Linden, Woodbridge, Springfield, and Clifton.