KNOX, Maine — The only thing sweeter than the smell of boiling sap is the maple syrup that pours from the cooker.

Sunday was Maine Maple Sunday, the annual celebration when residents and tourists get an opportunity to visit sugarhouses throughout the state and sample the nectar of spring. From York to Aroostook counties, sugar makers opened the doors to their sugarhouses for free tastings and demonstrations of how syrup is produced, from sap to table.

Maine produced 215,000 gallons of maple syrup last year, second in New England. Vermont topped the charts with a half-million gallons, according to the U.S. Department of Agriculture. All told, New England produced 870,000 gallons of syrup last year, more than one-half of all the syrup produced in the country.

Maple syrup and candy lovers lined up early at Kinney’s Sugarhouse on Abbott Road in this central Waldo County farming community. Lee and Mary Anne Kinney tap a 165-acre sugarbush that has been producing maple syrup and sugar products for the past five years.

Lee’s parents, Wes and Gwen Kinney, bought the property in 1977 after having operated a sugarhouse in Auburn for many years. The hillside parcel had produced syrup decades earlier, and the Kinney family spent the next 30 years preparing the sugarbush to produce sap once again. The work involved felling older trees, thin-ning the forest, removing brush and undergrowth and running plastic tubing from tree to tree throughout the piece.

Six years ago the Kinneys cleared a lot near the road, built their sugarhouse and opened for business. Lee Kinney said the 165 acres has 50 miles of tubing collecting sap from 6,325 taps, including 1,576 taps on a 30-acre parcel added this year. The trees, which are about two-thirds sugar maple and one-third red or silver maple, produce more than 100,000 gallons of sap per year. That converts into approximately 2,000 gallons of pure maple syrup.

Although the sap runs for only six or eight weeks beginning in early March, caring for the sugarbush is a year-round job, Kinney said.

“There’s a lot of work,” he said. “You have to take care of your trees, and we take good care of our trees,”

Wind is the business’s biggest enemy as fallen limbs or downed trees break the tubing that carries the sap to the sugarhouse. Deer can raise havoc as well, breaking tubing as they bound through the maples. Squirrels and porcupines prefer chewing the tubing.

The plastic tubing is supported by wires, and last winter, one wire was hit by lightning and 1,000 feet of tubing melted.

Kinney said he and his wife learned the craft by “visiting lots of sugarhouses” and attending Maple School, an intense three-day course that alternates annually from one syrup producing state to another. Maple School was held in Vermont earlier this year.

When the sap arrives at the sugarhouse, it is about 2 percent sugar. The consistency increases to 10 percent sugar after the sap is processed through a reverse osmosis concentrator. The concentrated sap not only speeds up the sugaring process, he said, it also saves money and energy.

“We’re doing in one hour what we used to do in four, and that’s important because the evaporator burns about 15 gallons of oil and hour,” Kinney said.

Kinney said the evaporator can convert 300 gallons of sap into 30 gallons of syrup in an hour. The syrup is filtered through diatomaceous earth — the fossilized remains of hard-shelled algae — before being stored in 40 gallon stainless-steel barrels.

Kinney said half of his annual yield is made into candy, with the rest going to Grade A light, medium, dark or extra dark syrup and other products such as maple cream and cotton candy.

Syrup and cotton candy were just what Samuel Grady, 8, and his family had driven over from Windsor to taste and take home.

“I love syrup and cotton candy,” Grady said, smiling as he clutched a bag of cotton candy. “It’s good.”

Leroy Brown, a retired gold prospector from South Thomaston, was a first-time visitor to Kinney’s Sugarhouse and also left holding a bag of cotton candy.

“Never been here or saw syrup being made before in my life,” Brown said. “It’s pretty neat. I like the syrup and I like the candy, too.”

Kinney acknowledged that although it may have taken awhile to get the sugarbush up and running, the company is debt-free, a situation that leaves it less susceptible to economic pressures. Standing next to a clear plastic pipe that enables visitors to see the sap as it flows from the sugarbush to the sugarhouse, Kinney said the ideal conditions were when the temperature drops to freezing at night and warms during the day.

“That’s when it runs the best,” he said tapping the pipe with his left hand, “And it’s running real good right now.”