Pizza riddle me this: It can ruin good pizza, can’t save bad pizza, and you even need it to make New York City pizza better. The average pizzeria relies on it and even most of the best still have to do it. If there’s a line you may not need it. If pizza’s hot from the oven you may get yelled at when asking for it.

What is it? The reheat.

“It’s like you do all this work, you make the dough, you make the sauce, you cut the cheese and you cook it, take it out, display it, and then at the last step, the counter guy could ruin the experience,” said Francis Basille of Artichoke Pizza. “He doesn’t leave it in long enough or he burns it. He doesn’t clean the oven.”

Forget the latest viral video about how to best reheat a slice at home in cast-iron. Even in New York City, the undisputed heart of America’s slice culture, increasingly, the pizzeria reheat is becoming a lost art. You can walk into far too many places and be given a reheat that’s either lukewarm or furnace-toasted.

What makes it so hard to get a good reheat? Is there a right way pizzerias should be reheating their slices? How long is too long? How long isn’t long enough? And should you, as a customer, always feel entitled to ask for a reheat?

These were the questions asked of some of New York City’s most respected pizzerias in an attempt to explore the nuances of an essential, oft overlooked and unappreciated but essential aspect of a good slice.

“The biggest mistake a lot of new spots do is they take the pie out and put it on a cooling rack,” explained Scarr Pimentel, owner of the vaunted Scarr’s on the Lower East Side. “That’s going to dry out the bottom. The good thing about the metal pans is they trap moisture in the slice. So when you go in for the reheat what’s going to happen? All that moisture’s going to evaporate and your slice gets crispy.”

Sal Vitale, third-generation pizza maker and an owner of New York City’s famed Joe’s Pizza is of the same school of thought, “When a slice sits on an aluminum tray, it could just come out of the oven and in two minutes, even though it just came out, it’s piping hot, it gets soft. You have to put it in the oven for 10 seconds just for the crispness. Even if the pizza is fresh.”

With one of the most famous shops in the city and a perpetual line out the door, Vitale’s idea of a reheat may be a little different. “I don’t think in my life I’ve ever seen a pie that’s longer than 20 minutes sitting down,” Sal said, adding there are different heating times for different styles. “Obviously a pepperoni and Sicilian go for a little more, but the cheese you can probably go 20 seconds. I’d say 20 seconds on a cheese slice is the perfect amount of time. On a pepperoni, you probably go to 35 to 40 seconds.”

Scarr Pimentel’s take is that it’s always going to be at least 45 seconds to a minute depending on how hot the oven is. For him, the key to a great reheat is for the pie guy to focus on the slice and see if it’s bubbling, “Once you see the microscopic bubbling happening that means it’s actually really hot.”

Like some owners, Francis Basille says he dedicates one oven deck just to slices. “We keep it at a lower temperature, 400 where everything else is at 500 or 550 depending on how busy it is,” he said. “I even put signs up to make sure you leave the slice in there a minimum of 60 seconds.”

According to Drew Brown, when he and Paulie Gee conceptualized what they wanted Paulie’s Slice Shop to be, their primary concern was consistency. They reheat warm slices for 30 seconds and room temperature slices for a minute and a half. “One of Paulie’s things, and I think he learned this from Chris Bianco, but the garbage pail is your best friend,” said Drew. “If something gets torched, we’re not serving it.”

You may notice that some slice shops use small conveyor belt ovens or countertop slice warmers for reheats. “That’s a smart idea because you ensure the amount of time,” said Basille of the conveyors. “It goes in one side, it comes out the other side. You can set it to 30 seconds, however fast you want it to go.”

As for the countertop warmers, “I don’t like the way they reheat,” said Basille. “I feel like you taste the oven on those small ovens, if that sounds nuts. But I do feel like you actually can taste the oven.”

So let’s say that the range for a reheat on a fresh slice out of the oven starts at 10 seconds in an oven deck dedicated to reheats, and a slice from a warm pie takes a minimum of 45 seconds to a minute. How about one of those pies sitting in a display at room temperature?

Tom Degrezia, co-owner of Sutton Place’s Sofia Pizza Shoppe, dedicates the front of the top deck of his oven to reheats and said that for a slice from a pie that’s been sitting out for five minutes, he reheats 60 seconds.

And how long is too long?

“If you reheat it too much you lose all the flavor,” Vitale claims. “If the cheese is cooked once,  you put it back in the oven and you leave it in too long, it gets extra hot again, all that cheese burns. It just boils. So you lose all the flavor. The perfect reheat is probably 20 seconds on a warm pie. For a room temperature pie, 20 to 30 seconds. You go over a minute, you start to lose flavor.”

While he has a personal preference, Artichoke’s Francis Basille hesitates to say how long is too long in the oven, “I think two minutes is going to make it really hot,” he said. “It’s probably a little overkill but there are some people that like it like that and they want it really hot.”

He’s right. After all, one customer’s extra crispy is another’s just-right.

“I ask every customer, and it’s exhausting because whenever I have to put a slice in, I’m like, ‘Do you like that warm, hot, or scalding?’” Degrezia said. “That’s the easiest way to get it right.”

— Arthur Bovino is a New York City-based pizza expert and contributor to The Sauce by Slice. He’s the founder of The Daily Meal’s annual list of the 101 Best Pizzas in America and author of “Buffalo Everything: A Guide to Eating in ‘The Nickel City’”. His writing has been featured in The New York Times, Bon Appétit, and Travel + Leisure among other publications. Follow him @nycbestpizza and thepizzacowboy.com.