Full of gas

By Paul Hetzler

While foods like beans and cabbage give us gas, there’s one case where gas gives us food. Fortunately, it’s not the same kind of gas.

Turns out, maple syrup is gas-powered. The reason maples run in spring is because their sapwood is charged with tiny bubbles. Carbonated wood — what’ll they think of next?

Not long ago, the best guess we had to explain sap flow was that water demand from developing buds pulled sap from the roots to the top. Trouble is, water can only be pulled vertically about 10 metres, at which point the column breaks.

Few trees other than maples have spring sap runs. The roots of birch and butternut create pressure to force sap upward, but maples have their own scheme. Maple sapwood contains fibre cells, which are partly filled with carbon dioxide gas. A lot of gas dissolves in cold sap, but it expands and bubbles out as temperatures rise.

Open a bottle of carbonated water that’s been in the sun and you’ll get a mini-geyser. An icy-cold bottle behaves similarly when opened. Same idea with maple trees. More or less.

On cold nights, gases in wood fibres shrink as they dissolve into sap. This causes a tree’s internal pressure to drop, creating a suction that draws sap up from the roots. As temperatures rise in the day, gases bubble out of solution and expand, increasing the tree’s internal pressure and forcing sap to the upper canopy.

Rather than flowing up from the roots and out the taps during the day as was once thought, sap flows down from the crown toward tap holes. When a warm day follows a sub-freezing night, sap may run for a few hours up to several days, depending on factors like barometric pressure and wind. If temperatures remain warm at night or below freezing during the day, sap won’t run.

All our maples yield sweet sap. Although sugar (hard) and black maples are most commonly used, producers also tap red maple if available. Silver maple is quite sweet, but they prefer wetlands and river banks — not places where maple producers typically operate. Even Manitoba maples, as well as Norway maples, which are an invasive species, can be tapped.

In addition to sucrose, maple sap contains organic acids, amino acids, minerals and other compounds. Maple syrup is a major source of manganese, riboflavin (vitamin B-2), magnesium, zinc and calcium.

And it could potentially delay or arrest dementia. In 2016, a Toronto-based research team identified a compound in maple syrup that inhibits beta-amyloid brain proteins from clumping. These clumps are strongly linked to Alzheimer’s disease, and blocking their formation might help prevent this tragic illness.

Recently, maple producers have branched out into value-added products like bottled maple sap, which, ironically, is carbonated. What goes around, comes around, it seems.

This article first appeared in the Québec Farmers’ Advocate. Reprinted with permission.