Maple syrup season

It's maple syrup season, that period of frosty nights and (slightly) warmer days that gets the sap pressure in the trees rising, and allows a simple tap drilled through the bark to produce sometimes prodigious quantities of dilute sugar solution - the raw material for maple syrup. Here at Harvard Forest we have a sap collection project to monitor any patterns in overall sap production over time. These are the sugar maples just below my apartment on Prospect Hill Road.

Our collection trees - at 8am it's still well below freezing, but it will warm up later.

The bolt holding the collection bag to the tree is hollow - this is plugged into the drill hole, and out flows the sap

Yesterday's sap waiting to be collected by Casey and Josh

While the purpose of the project isn't production, it's clearly a shame to waste the sap. Most of it goes to a nearby commercial maple syrup producer, but staff here can have as much as they like. So this weekend I picked up a large tub and got boiling. The sap is a very dilute solution - it's hard to distinguish it from water. While the commercial producers sometimes use fancy reverse osmosis techniques, the rest of us just have to boil. And boil. And boil some more.

Maple sap, (about a third already on the stove)

 I spent about 8 hours on Saturday, boiling the contents of this large bucket in a big stewpot on my stove, with the windows wide open to remove the steam.

Before and after!

The ratio of sap to syrup is about 40-1, although mine may be more since it's not very runny. But it tastes very fine, and I'm looking forward to sharing with family visiting later in the spring.

The exact mechanism of sap production in sugar maples is still the subject of some investigation - not least because different trees seem to vary quite a bit even when they are outwardly identical and on identical sites. As the temperature drops below freezing, sap is drawn up into the branches and the twigs, perhaps due to changes in the pressure of gas-filled cells. The next day, as the temperature rises above freezing, these gas cells expand and the sap flows back down - and out of the tap holes.

Part of the reason for the research is a concern over declining production days in New England as the period of cold nights/warm days shortens with earlier spring weather arriving courtesy of climate change. It seems very likely that maple syrup production will increasingly be dominated by Canadian maples. All the more ironic then, that the new Canadian $20 bill features a leaf that appears to many botanists (and me!) to be the leaf of a Norway maple - a species introduced to Canada and not useful for syrup production. The Canadian government has protested that the leaf on the note is merely 'a stylized blend of different Canadian maple species'. Yeah, right, one that looks uncannily like the Norway maple...