ST. LOUIS — Budweiser and Jim Beam, the Kentucky bourbon whiskey maker, have partnered to create a new beer that will launch later this fall.

In September, the pair will unveil a new limited edition beer called Budweiser Reserve Copper Lager. The beer will be brewed with two-row barley and will be aged on Jim Beam bourbon barrel staves to create a toasted oak aroma and nutty taste.

Last year, Anheuser-Busch InBev dug deep in the archives of its St. Louis brewery for a new beer called Budweiser 1933 Repeal Reserve.

Anheuser has rolled out numerous line extensions for Bud Light, but line extension for its flagship Budweiser is rare. Prior to the Repeal Reserve, the last Budweiser line extension was in 2012 when the brewery launched the limited edition Budweiser Black Crown.

Both the Repeal Reserve and Reserve Copper Lager come as market share for Budweiser continues to fall in the U.S.

Budweiser’s annual volume was down 7 percent last year, lowering it to fourth most popular beer in the U.S. behind Miller Lite for the first time. Bud Light is the top-selling beer in the U.S., followed by Coors Light, Miller Lite and Budweiser.