Officer Green wanted her vanilla latte piping hot. ''With vanilla on top, not a lot, just a drizzle, and very hot, don't make it warm,'' she shouted to Eddie Rodriguez, who was taking orders. He nodded and wrote Green on the side of a cup. ''Don't worry, I got ya. Extra hot for Officer Green.'' Then he slid the cup down the bar where Mr. Rodriguez and the other inmates in the barista training program at the Rikers Island prison complex were adding ice, steaming milk and grinding beans to load into a $3,000 Nuova Simonelli espresso machine.

It was rush hour at the coffee shop that pops up twice daily inside the staff lounge at one of the nation's most notorious jails. The uniformed guards formed a sea of blue in the dreary institutional lunchroom, with Maury Povich's talk show playing on an overhead TV and a smell of waffle fries and bleach in the air. They put in their specialty drink orders: a chai latte for a deputy warden (''not too sweet!''). Four shots of espresso for a guard headed into a long shift (''I need that extra kick''). Five orders in a row of the house specialty, the ''Captain T'': an iced caramel latte with whipped cream on top named after a favorite officer.

''Omar, you're an artist, kid!'' one guard said as Omar Jhury, 29, swirled the caramel syrup on top and peeled back a straw in a delicate petal shape.

''Whole lotta drizzles today,'' said Randolph Denis, 44, squeezing a zigzag of vanilla syrup atop an iced latte. During my visit, in late September, pumpkin spice, of course, was about to be in season.

Mr. Denis and the rest of the baristas (guards and instructors never call them inmates while they're in class) were convicted and sentenced to short city sentences at the Eric M. Taylor Center where roughly 730 inmates and 800 uniformed staff coexist each day, not always peacefully.

The barista class started in 2017 at the island's women's facility and was such a hit that the New York City Department of Correction expanded it to include 18-to-24-year-olds and convicted adult men. Over the course of four weeks, they have learned the nuances of customer service; the difference between dark and light roast; the intricacies of steamed milk.

''If it sounds like a piece of tearing paper, it's ready,'' Mr. Rodriguez said. ''You don't want to hear popping.''

The barista program (it's unpaid at Rikers) and a handful of others like it nationwide give inmates a new set of professional skills and a way to pass the time, but they also reflect a growing theory in the criminal justice system that the $88 billion coffee industry can soften the blow of incarceration and provide a critical link to employment. A job -- even one that pays $10 to $15 an hour, roughly the wage range at Starbucks -- can help end the cycle of crime and recidivism, experts say.

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