Checking Lines

The key is making sure it sucks as much as possible

Aside from meteorologists, there’s nobody more qualified to tell you when spring is coming in Vermont than a maple sugarmaker.

Sometime around the end of February or beginning of March, there’s a thaw. There are other, earlier thaws too, but this one is different: the vacuum releaser, at the very lowest point in the miles of plumbing strung over the mountainside, receives an unsolicited trickle of greenish sap. The trees whisper, in their language, we’re almost ready, and the race begins.

Unlike the hanging buckets of the past, the series of pipes and tubes that make their way downhill to a modern pump house don’t deliver sap through the force of gravity alone. We also use a vacuum pump. It applies the same premise as the vacuum in your house — create negative pressure in a hose so that whatever is at the end of the hose gets sucked into a receptacle. In your house, it’s gross; in the sugarbush, it’s sap. It might seem silly to try to literally suck extra sap out of maple trees, but the research backs it up: according to UNH extension, an efficient vacuum system can double the amount of sap per tree. Needless to say, an efficient vacuum system is a major priority on a commercial sugarbush.

The problem with maintaining an efficient vacuum in the middle of Vermont’s winters is that lower air pressure (like inside a vacuum, for example) actually raises the freezing point of water. That means that if there is a hole in one of our sap lines — from a squirrel chew, for example — the snow melt on a 34-degree day will find its way to that hole and, in the process of being sucked into the tube by the vacuum, turn into a block of ice, plugging the hole. This makes the system seem very efficient — computers at the top of each major sap line relay pressure data over a Wifi mesh network to the pump house, and the readings look good — but that same tiny block of ice will melt at 38 degrees, or 40, and then the vacuum will lose pressure in the same spring weather that leads to big sap runs. And you don’t want hundreds of tiny holes opening up on the biggest day of the year and costing hundreds of gallons of sap.

That’s why, every unseasonably warm day before the big sap runs start — and sometimes there are only a few — we grab our line repair tools, switch on the vacuum pump, rush up into to the woods, and then stop in our tracks. A good woods crew, even working together, will fall completely silent in unison, listening for the telltale hiss of a vacuum leak. The best of us can hear a leak the size of the period on this sentence from more than 50 feet away. We also learn to read the bubbles in the lines. A few are ok, but how fast do they move, and which way? And what happens when I pull up on this segment, or push down over here? Subtle changes in the speed or direction of the bubbles all tell us about what’s happening with the pressure inside the lines.

It’s all science, things like pressure differentials, surface tension, fluid dynamics, thermodynamics. But in practice out there, our tools are garden pruners, plastic connectors, and line splicers, not fancy gadgets. Watching the veterans check the lines, the science disappears and you see a master practicing their craft: listening and looking and hooking a gentle finger over the line to watch the bubbles and splicing and tightening and listening and trying to ignore the heaving breath and screaming hip flexors, and then sloshing on through two feet of melting snow in a never-ending pursuit of every last drop.

If you want some of the syrup I help make, you can order at https://ruggedridgeforest.com/.