Members of the book group, sporting matching gray T-shirts and broad grins, boarded the Napa Valley Wine Train in high spirits Saturday.

“The train is leaving the station! Choo choo!” member Lisa Johnson posted on her Facebook page, captioning a picture of five glasses of burgundy liquid clinking together.

But not long into the trip train staff began asking them to quiet down. Before the journey was half over, they were escorted off the train, where police officers were waiting for them, according to the Associated Press.

“We didn’t do anything wrong and we still feel this is about race. We were singled out,” Johnson told local TV station KTVU.

Wine train spokesman Sam Singer told the AP that staff had asked the book club members to either be quieter or get off the train. He said that people are asked to get off the train, which serves appetizers and drinks to passengers as they chug through California wine country, roughly once a month.

“The book club clearly was fun-loving, boisterous and loud enough that it affected the experience of some of the passengers who were in the same car, who complained to staff,” he said.

But on Tuesday, the Napa Valley Wine Train’s chief executive officer issued a full-throated apology for the company’s treatment of the members of Johnson’s Sistahs on the Reading Edge book club, saying the Wine Train was “100 percent wrong in its handling of this issue.”

“We accept full responsibility for our failures and for the chain of events that led to this regrettable treatment of our guests,” Anthony “Tony” Giaccio said in a statement, which was sent to The Post.

Giaccio said in his statement that he has spoken with Johnson and apologized for her group’s experience on the train. He also wrote a letter to the club, apologizing for the company’s “many mistakes and failures.”

“We pride ourselves our hospitality and our desire to please our guests on the Napa Valley Wine Train,” the letter stated. “In this instance, we failed in every measure of the meaning of good service, respect and hospitality.”

In the letter, Giaccio promised to make sure employees received more diversity and sensitivity training, and invited the club back on the train as his personal guests. The chief executive also noted that train employees were “insensitive when we asked you to depart our train by marching you down the aisle past all the other passengers” and said the company “erred by placing an inaccurate post on our Facebook site that was not reflective of what actually occurred.”

“Please accept my apologies for our many mistakes and failures,” he wrote.

“You can apologize but you can’t take away the experience we had,” Johnson told the Bay Area News Group. “We were still marched down the aisle of the train car to waiting police officers. I’m still traumatized by the whole experience.”

The apology came after the story of the Sistahs on the Reading Edge gained traction on social media, with many online using the hashtag #laughingwhileblack.

The women say that before they disembarked they were made to walk through several cars full of onlookers.

“It was very humiliating, very degrading,” Dininne Neal told KTVU, “and it made my mom cry, which made me cry.”

According to the AP, wine train employees called local police to report that “11 disruptive females” were being dropped off by the train.

“When we get off the train, the police are just standing there,” Katherine Neal told KTVU, “and they’re looking at us like, these are the unruly people?”

Police spokeswoman Maria Gonzalez said, “there was no crime being committed … nobody was intoxicated, there were no issues,” so the officers left. A bus came to take the women back to the train station.

In the past, she told the AP, police had responded to wine-train reports of passengers ousted for domestic incidents on board or for fighting.

A Facebook post from the company written after the incident obliquely referred to the book club’s ouster and accused the women of “verbal and physical abuse towards other guests and staff.” The post was later taken down, but not before Johnson took a screenshot and posted it online.

Singer told the New York Times that the post, written by a junior staff member, was wrong — the women had not been abusive — which is why it was taken down. He added that the incident could have been handled better — the group, which included an 83-year-old woman, didn’t need to be paraded through all six cars of the train, and perhaps the women could have been set up in another area. If the staff members had been being more considerate, he said, “they would have thought of another way to get them off the train.”

“We were insensitive when we asked you to depart our train by marching you down the aisle past all the other passengers,” Giaccio wrote on his apology letter. “While that was the safest route for disembarking, it showed a lack of sensitivity on our part that I did not fully conceive of until you explained the humiliation of the experience and how it impacted you and your fellow Book Club members.”

By Monday evening, the Napa Valley Wine Train’s Yelp page had been buried in negative reviews. One woman who said she was on the same train as the Reading Edge book club, wrote that she “watched in disbelief” as the women were escorted off.

“I’d like to think it wasn’t a racially motivated act, but given the fact that other, non-black guests were behaving in the same way and not removed, I can only conclude that it was discrimination,” she wrote. “This business belongs in the ‘what is wrong with our country’ category.”

This post has been updated.