Twenty years since its release, it’s fair to call Alexander Payne’s “Sideways” a classic, and even fairer to label this vintage dramedy a film that changed the culture — a couple of cultures.

It made Paul Giamatti a star and regular contender at the Oscars, lifted, expanded and extended the careers and of Virginia Madsen and Thomas Haden Church and thrust Payne’s then-wife, Sandra Oh, into the spotlight that led to her stardom.

It didn’t do the maverick movie-maker Payne (“Election,” “Citizen Ruth,””About Schmidt”) any harm, either. “The Descendents,” “Nebraska,” “The Holdovers” and two Oscars would make him the actor’s darling that he remains to this day.

And while wine was a pretty big deal pre-“Sideways,” its wine-wise/wine obsession changed that world, too. Merlot sales dropped and “pinot noir” became king of California and a big part of every vintner’s acreage and every wine-seller’s inventory in North America.

The film’s many locations became a tourist draw.

Bits of dialogue entered the popular lexicon.

“If anyone orders Merlot, I’m leaving. I am NOT drinking any f—–g Merlot!”

How does it play, twenty years on? Like a lovely vintage whose pedigree is no well-known, aging into intimate “special occasion” cinema. The wine analogies about it abounded from the first, and they’ve only grown richer with the years.

As I said in my review back in Nov. of 2004, “Payne has made a movie for the same sorts of people, one with body and ‘nose’ and character that movie lovers will savor long after the credits have rolled.”

Giamatti plays Miles, a self-described “loser,” temperamentally tardy and ethically “flexible.” He’s a San Diego middle school teacher living in a spartan apartment, a 40something divorcé with another overlong novel that no one wants to buy with his agent, broke and still driving an ’87 Saab convertible that he probably bought when he was young, about to marry and life had promise.

He’s taking a college pal, Jack (T.H. Church) north to wine country as a bachelor gift to an actor whose career peaked with a recurring role in a soap opera years before, a cocky charmer who is marrying money while his looks still hold up.

Miles is into wine, REALLY into it. He gets positively pedantic about the subject, even with the boorish Jack.

“First thing, hold the glass up and examine the wine against the light. You’re looking for color and clarity. Just, get a sense of it. OK? Uhh, thick? Thin? Watery? Syrupy? OK? Alright. Now, tip it. What you’re doing here is checking for color density as it thins out towards the rim.”

There’s one of the meanings of the film’s title, taken from the Rex Pickett novel it’s adapted from. You can’t get a handle on anything until you look at it “sideways.”

The other meaning gleaned from that title is how the trip turns sidseways thanks to Jack’s obsession with getting “Miles laid,” and his own desire to have a final fling before putting on a wedding ring.

Miles is a regular to the Solvang, Buellton, Santa Ynez Valley wine-stomping grounds. The fetching waitress he knows by name, Maya (Madsen), may or not be married, but Jack figures “She’s INTO you, man.” Jack starts badgering Miles to make a move.

Meanwhile, there’s Stephanie (Oh) the server at a local tasting room who responds to Jack’s flirtation with an extra generous pour.

“Oh, Stephanie, you bad girl.”

“I know, I need to be spanked.“

Miles and Maya talk about wine and life, with aspiring writer Miles godsmacked by Maya — Madsen at her most romantic and soulful — in a couple of monologues that’ll make you swoon, too.

Wine is “a living thing,” she says. “I like to think about what was going on the year the grapes were growing; how the sun was shining; if it rained. I like to think about all the people who tended and picked the grapes. And if it’s an old wine, how many of them must be dead by now. I like how wine continues to evolve, like if I opened a bottle of wine today it would taste different than if I’d opened it on any other day, because a bottle of wine is actually alive.”

Miles the wine purist has made the grape the one thing in his life he will not compromise about. But we’ve seen him steal cash from his mother (Marylouise Burke, terrific) to finance his “gift” to Jack. What we learn about how his marriage ended ironically fits in his grumpy reluctance to cover for Jack’s indiscretions. He’s not the dogmatic purist he claims to be.

The performances and situations age well despite the comical, pre-#MeToo vulgarity and sexism of it all. The locations lend the picture a pre “Sideways Tourism” beauty and unspoiled novelty that burnish director of photography Phedon Papamichael’s gorgeous warm glow moments, which blend into even its downmarket working class wine country look.

Madsen and T.H. Church landed meatier roles for a stretch after this film. Oh’s career took off — “Grey’s Anatomy” to “Under the Tuscan Sun” to “Killing Eve.”

Giamatti had played highly-strung villains — comical, mostly — in films before this. Here, he shows us blasts of that and a mopey, whiny, solitary self-awareness that became his brand, kind of that “character actor’s plight” — destined to “never get the girl.” When he won the Golden Globe for “The Holdovers,” he took the award with him, in his tux, to an LA In-and-Out Burger for a post-awards evening snack.

That was totally on-brand, most of us thought. That’s about as “Sideways” as it gets.

Rating: R, sex, violence, nudity, profanity

Cast: Paul Giamatti, Thomas Haden Church, Sandra Oh and Virginia Madsen

Credits: Directed by Alexander Payne, scripted by Alexander Payne and Jim Taylor, based on a novel by Rex Pickett. A Fox Searchlight release on Amazon, Youtube etc.

Running time: 2:07