Cornell Corner

5/16 vs. 3/16 no clear winner

Experts give overview on best practices for your lines

By PAUL POST | MAY 26, 2021

SHREWSBURY, Vt.—There’s a great deal of debate and no clear consensus among sugarmakers about the benefits of 5/16-inch versus 3/16-inch tubing.
One sure thing with either system is it's absolutely essential to keep tapholes free of bacteria and yeast, which build up and reduce sap flow, resulting in lost production and revenue.
In a recent webinar, New York State Maple Specialist and Cornell Maple Program Director Aaron Wightman outlined extensive sanitation research for both types of tubing to help producers enjoy the full rewards of all their hard work and effort.
He was joined by sugarmaker Arthur Krueger of Krueger-Norton Sugarhouse in Shrewsbury, Vt. and a noted 3/16 tubing pioneer.
The trials Wightman described were conducted at Cornell’s two 7,500-tap research sugarbushes at the Arnot Forest near Ithaca, N.Y. and at Uihlein Center in Lake Placid, N.Y.
“We aren’t just doing our research in a Petri dish,” Wightman said. “A lot of these treatments we’ve tried on thousands of trees. These aren't hypothetical research concepts. We’ve actually tried them on a large-scale, commercial setting. So we have that experience to back up the evidence.”
He started by giving a brief description of the freeze-thaw cycle that creates a pressure-vacuum cycle within trees, which makes sap flow.
“That’s really critical for understanding why taphole sanitation is important,” he said. ”When maple trees experience temperatures above freezing and thaw, and cells inside the tree begin active metabolism and gasses that have accumulated within the tree expand and heat, the tree actually generates positive pressure.”
This pressurization is what squeezes sap out of the taphole.
“The flip side is, when temperatures drop below freezing all those gasses inside the tree shrink and that creates a vacuum,” Wightman said. ”That’s what draws more water up into the tree so sap will flow during the next pressurization cycle.”
The important thing to understand is, this tube tapped to the tree is submerged in sap, he said. When a tree freezes it sucks sap back up out of the collection system.”
However, this sap is contaminated with bacteria and yeast because it's been exposed to the environment.
”We’re trying to prevent that because that’s what keeps the taphole from being productive, typically late in the season in late March or early April,””he said.  “It’s not because the tree isn't capable of producing more sap. It’s just that the taphole was slowly being contaminated with bacteria and yeast, and those multiply and block the vascular tissue so it can no longer push sap out the hole.”
Wightman then presented four different sanitation methods to keep microbes from finding their back way back into tapholes. 
They are: mechanical, antimicrobial treatment materials, sanitizing agents and tubing replacement.
“We use the term taphole sanitation but what we're really talking about is taphole longevity,” he said. “We’re trying to keep tapholes productive for the longest amount of time because that’s what is going to give us the most sap at the end of the season.”
Wightman pointed out that 5/16- and 3/16-inch tubing have different properties that require different treatment strategies.
There’s a great deal more information about 5/16 because it’s been around since the 1950s with decades worth of research involved.
But 3/16 is much newer, which means determining best practices for sanitation is still a work in progress.
When a tree is in its vacuum state, sap is only sucked back up 12 inches with larger 5/16-inch tubing, so the drop line and spout are the only things producer need to worry about. 
But with 3/16, sap is a solid column held together by cohesion.
Most often, 12 feet of sap is pulled back and Wightman cited one instance in which 40 feet of sap was sucked back. So just treating the drop line and/or spout isn't adequate.
Research on 5/16-inch tubing found that installing new spouts and drops resulted in an average 82 percent increase, or 13 more gallons of sap per tap, over time. 
In one year, 2010, there was a 150 percent increase.
“That’s a good indicator of how critical it is to prevent microbes from getting pulled back into the taphole,” Wightman said.
But replacing spouts and drop lines each year is somewhat wasteful and definitely time-consuming. 
Treating them with bleach is an effective, tried-and-true alternative. Tests revealed a 72 percent increase in yield.
Wightman suggested mixing 200 parts per million or one tablespoon of bleach per gallon of water. 
Equipment should be submerged for 20 minutes, followed by thorough rinsing and drying. “
“Move them around to make sure bleach flows through the drop line and comes in contact with all surfaces,” he said. ”There are a lot of clever ways people have come up with to get good contact time.”
Some people strap drop lines to a rotating drum that repeatedly dips drops into bleach.
“It may sound like a lot of work, but this is a fairly practical approach,” Wightman said. “It’s very feasible and cost effective.””
Another sanitation option is the use of check valves, which have small rubber balls inside. When a tree is flowing the ball gets pushed out allowing sap to come out. 
During the vacuum cycle it gets pulled back against the spout opening and blocks sap from getting back into tree.
Tests involving check valves produced a 72 percent increase in sap yield, equivalent to bleach.
The caveat is they’re typically only good for one year, so it’s not a maintenance-free method, Wightman said. “Most people install new ones when they tap.”
Sanitizing with peroxide isn't good because it requires oxygen to be effective. So if it’s not exposed to air it’s not a useful solution.
Researchers also tested silver spouts, which have ionic silver imbedded in plastic, similar to medical tubing. 
The silver serves as a sanitizer that kills bacteria and yeast passing through the system. 
These spouts worked well the first two years, but only produced a 20 percent benefit in year three.
Cornell initially tried three different ways to sanitize 3/16-inch tubing, none of which proved very effective.
They tried using 5/16-inch drop lines, silver spouts, and putting check valves in spouts and drop lines.
“We weren't even close to what we were hoping to achieve, so we had to go back to the drawing board and come up with a new set of treatments,” Wightman said.
Almost by accident, while relocating experimental treatments during a tree-thinning project, they quickly discovered a much larger issue. 
Relocated lines required new Ts, which achieved much higher production.
”That was a really strong indicator that there was a bigger problem,” Wightman said. ”Clogged Ts are the big story of why 3/16 tubing starts underperforming compared to 5/16 tubing.”
To attack this issue, they adopted several new strategies tried for the first time last season. But there were problems with each one.
First, antimicrobial 3/16-inch Ts, purchased from a medical supply company,were tested.
“But they aren't durable,” Wightman said. ”They’re meant to be used indoors in a medical setting and require careful installation. I don't know if they’ll hold up over multiple seasons.”
Next, researchers tried quarter-inch Ts and quarter-inch microbial Ts. 
But an expander was needed to fit them into 3/16-inch tubing, which proved difficult and some Ts popped apart during the season.
”Quarter-inch Ts are really hard to work with,” Wightman said. “I’m not sure that’s going to be a long-term solution.”
Lastly, they tried a sanitation technique by using hand pumps to inject lines with calcium bleach (200 ppm), which was left for a week and drained out. “
This worked pretty well, but didn’t restore productivity to the same level as all new 3/16-inch tubing, Wightman said.
”Overall, I don't think we’ve hit on a winner yet,” he said. “Basically there are a lot of strategies that work really well for 5/16 tubing, but we still don't know what to do with 3/16-inch tubing. This is the research I'm going to pursue further next year.”
In 2013, Krueger obtained a grant from the state of Vermont to switch his gravity-fed, 2,400-tap operation to 3/16-inch tubing, which has a natural vacuum benefit. It was the first commercial-sized application of this technique in the state.
He said 3/16-inch tubing handles one-third the volume of 5/16, so there’s much more potential for contamination. “The other issue is clogging, he said. “
“There’s many different types of bacteria in the sap,” he said. “You’ve got to deal with them because they cause can taphole contamination and clog lines.”
Replacing spouts and/or check valves is fairly expensive.
Instead, Krueger sanitizes lines with a calcium hypochlorite bleach product called Zappit.
First, after the season's done, he flushes mainlines with fresh water, pumped up from the bottom, to remove unwanted material. 
Valves are opened at the end of each mainline and closed when the process is done.
Next, he creates a 400 ppm bleach solution by mixing a one-pound bag of Zappit in 200 gallons of water, using an old bulk tank. 
Then bleach is pumped up from the bottom into lateral lines.
He suggested mapping out lines, having crews do a walk-through ahead of time, and using walkie-talkies to maintain contact between the pump operator and people in the woods.
The webinar was the latest session of an online series called "Out of the Woods: Enriching your Maple Business,"”organized by Ohio State University, Penn State University and Future Generations University of West Virginia.