And then, well, the lid blew off. As the center's chief executive officer David Eisner proposed a toast, and the guests soberly raised their (cider) glasses, sirens started to scream, and trench-coated and fedora-ed Prohibition Enforcement Agents burst in, shouting warnings and confiscating the "illegal" bottles of wine.
The Constitution Center hasn't skimped on the energy and antics with this latest high-profile exhibition - the center's first major touring show (after a disappointing Springsteen gate) and possibly its most bulletproof to date.
With a $400,000 grant from the National Endowment for the Humanities, and signed touring contracts with museums from Austin to Seattle, it's starting off in the black.
And with a bang. Just hours after the temperance-friendly lunch, you could find classic cocktails, small-batch whiskey, and Batch 19, a pre-Prohibition-style lager, flowing freely at a Bootleggers Ball in the center's lobby, a jazz band belting away near a shiny, black 1929 Buick Marquette - a six-cylinder job once referred to as a "Whiskey 6" because hooch smugglers souped it up to outrun the law.
But between the grainy footage of Roaring Twenties flappers kicking up their heels and soundtrack blasts from tommy guns; between the spooky voice behind a fake speakeasy door and the get-your-mugshot-taken-with-a police-lineup cutouts (of Al Capone and his gangster pals) - there's a sobering, provocative, and indeed timely tale here etched with caution and drenched in regret.
It goes like this: Look upon the wreckage caused by this most unpopular, and the only repealed, constitutional amendment (the 18th, adopted in 1920).
Look at the criminality it unleashed, and the hypocrisy it institutionalized (there were rabbis by the name of McGuire purchasing sacramental wine) during its 13-year run, and consider the legacy of an energized minority of the population stuffing morality down the unwilling, parched throats of the majority.
Those who see commonalities between the banning of booze and the civic perversions and injustices of the war on drugs will find fresh argument in these halls.
To Daniel Okrent, the exhibit's curator, the Prohibition era offers a powerful object lesson. He expresses it at the podium, and he drums on it in the audio tapes that guide your tour. And this is it: "Prohibition is a reminder to be wary of those offering a panacea."
And this: "It is a lesson in how the democratic process can be manipulated by democratic means."
And this: "Beware [of the toll] of single-issue politics" that can ride roughshod over proportion and a "larger sense of the civil world."
The 18th Amendment, finally, he says, may be a wild card in our constitutional history, but it came into place through "the deployment of political tactics and strategies still in play today."
It is Okrent's prodigiously reported 2010 book, Last Call: The Rise and Fall of Prohibition, that is the emotional and intellectual template for the exhibit. (If his name sounds familiar, he was for several years the public editor of the New York Times.)
From the distance of 90 years, Prohibition can seem a freak storm. But it was in a way a perfect storm combining waves of German immigration, Southern racial agendas, women's disgust at saloons and powerlessness at the polls, a federal income tax that made liquor-tax revenue less essential, and masterful political lobbies.
And if the exhibit has a strong suit - and it frankly has many - it is explaining how something so radical and so unpopular became, step by step, the law of the land.
The national pastime of drinking had metastasized: Empty bottles on one wall depict the amount of booze the average American was drinking in 1830 - about 90 bottles of 80-proof liquor a year, three times greater than the current level.
Even the hard cider that fueled rural America (partly because drinking water was often impure) was spiked with 10 percent liquor to keep it from spoiling. From before the Civil War until 1890, the industrialization of national brewery brands resulted in the consumption of hundreds of millions more gallons of beer.
Laborers drank away their wages. Wives and daughters were regularly abused by drunkard husbands and fathers.
All-male saloons sponsored by the big brewers (Anheuser-Busch chief among them) tripled to 300,000 by the turn of the last century, fueled by commercial tie-ins and waves of European immigrants.
For their part, many women found themselves addicted as well, to so-called home remedies like Lydia Pinkham's Vegetable Compound "for female complaints" that contained a whopping 20 percent alcohol.
The artifacts are all here, the displays interrupted now and then by a dance floor showing the foot moves of the Charleston, and a (dry) bar featuring old Philadelphia cocktails, including the raspberry, gin, and egg white Clover Club, recently spotted at Hop Sing Laundromat, the latter-day "speakeasy" tucked off Race Street in Chinatown.
There are the vivid handbills warning of the scarring effects of booze. There is the medieval-looking saloon-bashing hatchet once wielded by Carrie Nation. And the silken banners of Frances Willard's robust Women's Christian Temperance Union, near the banners of the women's suffrage movement, causes that became bound up in each other as women joined forces for alcohol reform and voting rights.
There is the "amazing amendment machine" of Prohibition's chief architect and tireless lobbyist, Wayne Wheeler. Exhibitions of jazz, and changing social mores, and the spread of a dance called "the shimmy." And all the rest of the ingenious dodging - smuggling trucks with fake brick doors, parishes that poured parishioners bottles from over-orders of sanctioned sacramental wine, brass knuckles, submachine guns.
In its serpentine, dim-lit precincts, the exhibition is quite a ride.
While it lasts. Then suddenly you're back blinking in the brighter light of the center's lobby, and considering again this question: Does the power of single-issue politics haunt us still?
Has it hogged way more of the nation's microphone than is healthy in a democracy?
And finally this: Where does a guy get a drink around here?
"American Spirits: The Rise and Fall of Prohibition" runs through April 28 at the National Constitution Center on Independence Mall. For ticket and other information call 215-409-6700 or go to constitutioncenter.org.