If there is a true nectar of the gods, some would argue that it flows not from an ancient fountain in a hidden land, but from a small hole drilled in the side of a New England maple tree.

Of course, the clear, raw sap, which holds just a hint of the sweetness of the final product, has to be boiled down before it takes on the sparkling golden-amber hue and the distinct woody flavor that Mainers will pour on just about anything from pancakes to ice cream.

And it’s the gathering of the sap and the boiling-down process that makes the maple syrup business such a labor-intensive one for folks like Tim Littlefield, owner of Lucerne Maple Products on Route 46 in Holden. Littlefield’s operation will be one of the many maple syrup houses that will be open to the public this Sunday as part of Maine Maple Sunday, an annual open house sponsored by the Maine Department of Agriculture and the Maine Maple Producers Association.

The process of turning 40 gallons of raw sap into just one gallon of maple syrup has become more high tech since American Indians first began tapping trees, but no one knows exactly how the practice began, according to Littlefield.

One story, heard years ago, holds that one winter, an American Indian stashed a piece of deer meat inside the hollow of a tree that had been struck by lightning. In the spring, the sap began to run and by the time the Indian came back, the meat had been marinated in the fluid and had taken on an exquisite flavor. Fortunately, he remembered what kind of tree it was, and by the time white settlers arrived, the natives had developed a practice of tapping trees and making maple sugar and syrup.

Their tapping methods were different from the methods used today, Littlefield told a visiting group of youngsters last week.

“They would cut a notch in a maple tree and stick in a reed at the bottom of the notch,” he said. “The sap would drip into a container, probably a birch-bark container.”

The boiling-down process also differed from the modern methods, he said.

“They would set up a carved-out log next to a fire and fill the hollowed part with sap,” Littlefield said. “Then they’d put a rock in the fire and heat it up and when it was hot enough, they’d put it into the sap.”

The heat from the rocks would begin to evaporate the water in the sap, eventually creating some kind of syrup or, depending on the number of rocks used, a product he called Indian sugar.

“We’ve gotten pretty high tech compared to them,” Littlefield said, although the basic steps of getting sap and boiling it down have remained the same.

Instead of notching the maple tree, Littlefield drills a small hole into the tree using a portable, electric drill.

He uses hard plastic taps, replacing the old metal taps. Instead of metal buckets hung on the taps, Littlefield and most commercial maple syrup producers now attach tubing to the taps. The tubes run from the trees to a larger plastic line that carries the sap to a collection tank near the sugarhouse.

Although crews still have to go into the woods to tap the trees, the use of tubing has reduced the amount of labor dramatically. It’s also increased the quality of the sap, he said.

“You don’t have any dirt, or bugs or leaves in the sap,” he said.

At the sugarhouse is where the real work begins. It’s also where the real technology kicks in.

Before it heads to the evaporator, itself a maze of partitions through which the sap moves as it thickens, the sap is run through a reverse osmosis process, which pressurizes the sap so that some of the water is forced through a membrane that separates it from the sap.

“It can take out about 70 percent of the water before I start boiling,” he said.

That saves a lot of time on the boiling process and can increase the amount of maple syrup he can make.

During the process, Littlefield said, he’ll go through about 13 gallons of oil per hour to keep the sap boiling.

“It sounds just like Rice Krispies in here,” he said. “You get that snap, crackle, pop, it’s boiling so hard.”

Nothing can replace the boiling process, because it’s there where the remaining sap is turned into tasty syrup.

“You can’t make maple syrup without heat,” Littlefield said. “It’s the scorching of the sugar crystals that create the color and the flavor.”

That’s also why there are different grades and different colors of syrup.

In order to be maple syrup, the final product has to contain 66 percent sugar, Littlefield said.

The sap early in the spring has more sugar in it than the runs later in the season, therefore it takes less boiling to get to that 66 percent level.

Less cooking means less scorching of the sugar crystals, which results in a lighter color and a more delicate maple flavor.

The grades of syrup have been well established and each producer has to match the correct flavor with the correct color, he said.

The light syrup is very sweet, but doesn’t have much maple flavor, he said.

As the season goes on, the sugar content in the sap decreases and the sap has to be boiled longer to render the 66 percent sugar. The longer the boiling process, the darker the syrup.

“In the middle of the season, you get a medium color and a more robust, more maple flavor,” he said.

“Then the darker amber is an extremely jump-out-and-get-you maple flavor. Then there’s the extremely dark color that is a little on the rugged side for some people.”

Visitors to Littlefield’s operation and to others around the state on Sunday will get a chance to watch the process and to sample some of the final product. Most of the sugarhouses offer free tasting and live demonstrations of how the syrup is produced. Others, like Littlefield, offer samples of other treats made with maple syrup.

“It’s a lot of fun and you get to meet a lot of people,” he said. “We’ve made friendships that have lasted for years.”

But Maine Maple Sunday, which is always the fourth Sunday in March, is more than just a family day to tap into a New England tradition.

It’s the single largest retail day of the year for Littlefield and many other maple syrup producers. Although a lot of their product is sold commercially in large quantities, Littlefield and other producers also package retail-size containers for sale at their sugarhouses or in local markets.