As the happy-hour crowd began trickling into The Celtic Tavern on Tuesday night, bar owner Patrick Schaetzle — flanked by placards and mirrors touting Murphy’s Irish Stout — got some unsettling news.

Sometime next year bars will have to stop selling his Lower Downtown pub’s signature stout along with an array of other beers that are lower alcohol. The looming restrictions flow from a bitter, three-year battle between liquor and convenience stores over who can sell full-strength beer.

Schaetzle and a number of his similarly shocked patrons pointed out that both waistlines and blood-alcohol levels could suffer as a result of banning low-alcohol — read, low-calorie — beers from taverns and restaurants.

The Celtic could carry another stout — Guinness teeters right at the cutoff point between the low- and high-alcohol label — but Schaetzle won’t be happy about giving up a brew he feels is more authentically Irish.

“It’s ridiculous,” he said, grabbing for a bottle of wine under the bar. “I don’t understand why the nanny state would (ban beers) when the other stuff is three, four and five times more alcohol by volume. It’s going to hurt a lot of places.”

State liquor regulators continue to hammer out guidelines meant to ensure everyone from the brewers down to the retailers follow the rules.

Beermakers will have to test their suds and submit an affidavit stating their alcohol content to authorities.

Once enforced, the rules will likely shut off taps of lighter versions of brands like Shiner, Amstel, Heineken, Yeungling, Michelob and Shipyard among others. Light versions of the big three — Coors, Budweiser and Miller — appear to have just enough alcohol to remain flowing.

Technically, bars, restaurants and liquor stores in Colorado should never have sold the lower-alcohol beers in the first place, though no one ever paid much attention.

Their licenses allow them to sell spirits, wine and beers that fall into the “malt liquor” category: Brew stronger than 4 percent alcohol by volume or 3.2 percent by weight.

Convenience and grocery stores’ licenses are restricted to selling only beer at or below that threshold, thanks to rules aimed at limiting the flow of alcohol to the general public.

Blocked for years in their attempts to sell all types of beer, convenience store advocates and their allies in the legislature amended a bill last spring that now requires the state to enforce license restrictions to a T.

“Either stop selling the product we sell, or let’s stop having this false delineation on beer,” said Jason Hopfer, lobbyist for a group of convenience stores. “Let’s let beer be beer.”

Colorado has never reprimanded a bar or liquor store for selling beer that’s not alcoholic enough, as far as liquor enforcement director Laura Harris knows.

Even punishment going the other way — dings to convenience and liquor stores selling beer with too much alcohol — are rare, though in the 1990s the state revoked the license of a distributor, Harris said.

She cautioned that the rules will take effect gradually, starting with the beermakers and working down. It could be spring before consumers notice a change.

“Brands will either stay in the market appropriately labeled or leave the state,” Harris said. “These things don’t turn on a dime. We’d rather spend our time on more important public- safety issues.”

Restaurateurs caught in the middle of the liquor-store-convenience-store face-off hold out hope that lawmakers will intervene in the new year.

“We’re not really involved in this fight,” said Pete Meersman, president of the Colorado Restaurant Association. “Our members feel like they ought to be able to sell the stuff. Yes, we’re worried about it. But there’s a legislative session starting Jan. 12. A lot can happen.”

Convenience store advocates are drafting bills now, and Meersman’s group has already started lobbying lawmakers for a fix.

A commonly discussed resolution — and one that liquor-store owners abhor — is abolishing the low-alcohol beer designation altogether.

Massachusetts transplants Tom Maloney and Jen Cutter wouldn’t mind letting retailers sell whatever types of beer they like — especially if it would keep bars from shutting down taps.

The pair sidled up to the bar at The Celtic on Tuesday and argued that taking away low-calorie and low-alcohol options at bars would hurt public health and inconvenience consumers.

“In a lot of ways, they’re safer beers to drink,” said Maloney, who sticks to low-alcohol beer when he’s skiing. “It’s really just another way for state government to make things complicated.”

Jessica Fender: 303-954-1244 or jfender@denverpost.com

About the law

The law requires to-the-letter enforcement of the state’s existing beer regulations. Bars, restaurants and liquor stores can sell only beer that is above 4 percent alcohol by volume. Grocery and convenience stores are allowed to sell only alcohol with less than 4 percent alcohol by volume.