In the lull before the first crush of happy-hour drinkers will crowd into Oyster House in Center City, the waitstaff is gathered around a table in the corner.

After an update on the day's specials from sous chef Patrick Alfiero ("We're verballing shad roe again"), bar manager Colin O'Neill takes over, passing around samples of Barr Hill Gin, made by Vermont's Caledonia Spirits, and narrating the history of the drink and its creator.

"Todd Hardie was a beekeeper. He bought his first beehive in 1976, when he was 12 years old, and has been keeping bees ever since," he says. "This gin has only two botanicals, juniper and Caledonia honey, but, depending on the season, this gin can change quite a bit. In the summer, it can be much more grass-forward."

This 15-minute briefing for Oyster House staff is perhaps Philadelphia's longest-running and most thorough gin-education program. It includes a talk, a fairly detailed cheat sheet, a tasting of a gin-of-the-week, and a sample cocktail created with the gin. It can get pretty wonky as the team discusses the gin style (in this case, the style is Old Tom, meaning it's sweetened after distillation)  and tasting notes.

Gin and oysters may be a classic combination, but Oyster House shows an above-average commitment to the notion. It stocks 54 gins, making the bar one of just a handful of gin specialists in the city.

It's part of an American gin revival that is slowly growing interest in a spirit that's been overshadowed in recent years by bourbon and rye.

There's now more gin being made in this region than at any time since Prohibition. That includes new craft distilleries in Manayunk and Chester County, as well as Bluecoat maker Philadelphia Distilling, which launched in 2005 and has since grown enough to upgrade to an impressive new distillery and cocktail bar in Fishtown  this year.

"Nobody was talking about gin in 2005. It was the vodka rush, and a new Russian billionaire was launching a vodka every two or three weeks," said Philadelphia Distilling president Andrew Auwerda. "We felt like we had to zig when everyone else was zagging."

So they decided to create an American-made dry gin as an alternative to Tanqueray or Bombay Sapphire.

"The gin category itself is not explosive, not like a bourbon or rye whiskey right now, but there is growth and interest from millennials," he said.

More recently, Philadelphia Distilling launched a barrel-finished gin, an oaky, caramel-colored spirit meant to lure whiskey fans.

Since then, other artisan gin makers have entered the market, spurred by the resurgence of craft cocktails, the culinary creativity inherent in gin making, and the relatively low barrier to entry, compared to whiskey.

Among them is Riannon Walsh, who was a longtime whiskey-maker and consultant before becoming a gin maker and "master blender". When a prospective business partner contacted her about opening a distillery — spurred in part by reforms in Pennsylvania state law providing for small craft distilleries — she saw an opportunity.

"With whiskey, you have three to five years ahead of you. It takes us two and a half weeks to make a gin and put it in a bottle," she said.

They started Brandywine Branch Distillers in Elverson, Chester County, and launched a line of high-end, small-batch gins under the label Revivalist. Instead of starting with a purchased neutral grain spirit (that's how Philadelphia Distilling, and many others, do business), she ferments, distills, and infuses her gins in-house, a process she likes to call "grain-to-bottle" distilling. The line of gins includes one for each season, infused with botanicals like mint, coriander, and citrus for spring, and orange, nutmeg, and clove for fall.

She sees the gin craze in Europe − which had record gin sales last year, and the opening of 100 new gin distilleries in the last few years alone -- as a promising sign.

"Spirit trends tend to start in Europe, then move to America," she said. "People are starting to realize that gins are not your father's Tanqueray. Craft distilleries are making really interesting gins all over the country now: Everything from pine-needle-infused gins in California to blueberry-infused gins in Maine to what we're doing here, and critics are starting to pick up on it, as are bartenders."

In Manayunk, Walter Palmer takes a more traditional approach with his Palmer's Liberty Gin, based on an antique recipe he found in an 18th-century Dutch manuscript, with coriander, lemon peel, cardamom, and other botanicals.

The Palmer Distilling origin story, on the other hand, is a very modern one. Palmer lost his job running a construction trade association after 27 years and couldn't find work, so, he said, "I decided to take control of my own destiny." He started the company in 2014, and began selling gin the next year. He's now up to about 300 bottles a week.

Palmer had a romantic idea of making whiskey, but warehousing all those barrels alone seemed cost-prohibitive. Instead, he found the beauty in more economical gin; he made 53  variations on the Dutch genever recipe before finding just the right one.

Now, gin-makers like Palmer and Walsh are hoping more bartenders will become gin specialists. There's a Revivalist-based cocktail on the menu at R2L, and a Palmer's Liberty Gin martini available at Barclay Prime. M Restaurant at the Morris House offers gin flights for those who want to get technical about it. And distillers like Philadelphia Distilling and Brandywine Branch have created their own bars and tasting rooms to boost interest in the drink.

At Oyster House, where O'Neill has been preaching the gin gospel for a couple of years now, the good word is slowly reaching more customers. He keeps about six gin cocktails on the menu and often spends hours calling distillers or researching online to identify the botanicals, which can range from herbs to dried fruit, spices, or, as in the Barr Hill Gin, honey.

"It's a lot easier to make a cocktail if you know what's in a gin," he said.

And he'll keep running those classes. "It's one thing to have 54 gins," he said. "It's another to have a staff that knows what you have on the shelf."