We started tapping the trees the last week of January. Stan picked out three sugar maple trees on campus for us to tap: two on Wallace Dr. going through the South 40 and one near the intersection of Forsyth and Wallace. In order to get best sap flow, we placed the taps on the side of the tree that would get the most sun. We drilled a hole in each tree about 2-3 inches deep and hammered the tap (a long metal tube that was open on both ends) into the hole, then attached milk cartons to the open end with some wire. Everyone signed up for a day or two to collect sap; on warm days (i.e. days that were above freezing), the milk cartons could fill up completely, so we had to make sure we emptied them so they didn’t overflow! We collected sap for about three weeks, but only a handful of those days were warm enough for sap to flow in the trees. Regardless, we collected enough sap for a delicious pancake breakfast!
On the day of the breakfast, Stan and one of the head chefs, David Rushing, came into Ibby’s early to start boiling down the sap. On its own, the maple sap is basically water with a little sugar in it; you could just barely taste a difference from tap water. However, it does have about 2-3% sugar content, so boiling it down to about 60% sugar creates the delicious breakfast topping we call maple syrup! Stan and David boiled down the maple sap all morning, and David, with his extraordinary culinary expertise, used some of the edibles Stan brought with him (acorns we had shucked and frozen the previous semester along with some berries Stan had collected) to create a delicious breakfast spread. We had acorn pancakes and waffles, berry compote, fresh fruit and, of course, the star of the show: our homemade maple syrup! Members of the Burning Kumquat (the student group that runs the on-campus urban garden) who helped us collect sap were also there to enjoy the (literal and figurative) fruits of our labor! The breakfast was absolutely delicious, and informative, too; Stan discussed the science behind collecting sap (see below) while David and other members of Dining Services talked about Wash U’s commitment to using locally-sourced ingredients.
Entry by Annie Gocke
Trees, being the enormous organisms that they are, need to store huge amounts of fuel to keep them alive during the winter. During the spring and summer, trees produce their fuel in the chloroplasts in their leaves, taking in sunlight and carbon dioxide from the air and transforming them into sugars and organic compounds. Trees then take these compounds and using long, thin tubes called Phloem, transport the nutrients down for storage in the roots. When the leaves fall and the seasons change to the point where trees can no longer perform photosynthesis, they survive on the saved fuel. As spring comes around again, the nutrients must be moved back up the tree to the buds so that leaves can grow again and the tree can save for the next cycle. It is this process that humans tap into. The transport of the nutrients is the subject of much study in the scientific world but there is a general consensus that water is responsible. Water molecules are charged so they have a positive end and a negative end. Since opposites attract, the water molecules link to form one long chain that can pull all the nutrients and other water molecules up as the water molecules higher up in the tube evaporate and pull the nutrient rich sap up. This occurs in the xylem, another set of tubes that works with the phloem for transport inside the parts of the tree. The only problem with this process is that it is painfully slow and not enough to yield sap for human consumption. Luckily, another property of water actually provides us with a steady flow. Water, unlike most every other known chemical, actually expands when it freezes. This expansion follows the path of least resistance (i.e. up the empty xylem tube) and as it melts, it provides a lot of liquid sap for us. Therefore, the best time of the year to harvest sap is when the nights get below freezing point and the days go above, so that there are waves of freezing and thawing to push the sap up and out. Before then it is too cold for the freezing expansion to mean anything and afterwards it is too warm for the freezing/thawing process to provide the steady flow that it does. When it is too warm out the xylem continue to allow evaporation and the attraction between the charged sides of a water molecule to pull sap upwards, which is very slow.
Entry by Neil Stein
Note:
If anyone is interested in tapping trees, check out the website Tap My Trees. They have a lot of information on tapping trees and good resources to get started!