What a perfect spring ... for making maple syrup

Wow, what an April, lots of snow and a ton of maple sap. Just as Twins fans remember 1991, ricers remember that great crop with no rice worms, and skiers remember the year of perfect snow, I will remember 2019 as a great year of maple sap flow. This season of tapping maple trees was blessed with the perfect combination of freezing nights and above freezing days lasting for a few weeks, at least where I was tapping.

I had a ball, snowshoeing with a sled the first part of the season and ending up with rubber boots and hauling buckets by hand.

Most of you know that your real maple syrup comes from the maple tree; it is not the same as Mrs. Buttersworth's. I just checked the ingredients of Mrs. Butterworth's Original Syrup; here are the first four (maple syrup is nowhere on the list):

1. high fructose corn syrup

2. corn syrup

3. water

4. cellulose and gum salt

Try some real maple syrup someday.

Let's explore what causes sap to drip out of maple, birch, and box elder trees during this time of year. The sap that is collected is on average about 3 percent sugar as it exits the tree; we then boil it until it is about 66 percent sugar and is officially maple syrup.

I think I will go have a spoonful right now .... Wow, that was good! Sometimes I drink the cold, clear, subtly sweet sap right out of the tree.

The process that causes sap to flow is quite complicated, and as recently as 1997 the understanding of sap flow was upgraded with some new research.

Time to dig in and try to understand the current understanding of this phenomena. I have included a drawing showing the location of xylem and phloem and their surroundings within the tree.

Trees are vascular plants, meaning they have vessels running from the roots to the uppermost leaves. This vascular tissue lives right under the bark and moves out a little every year, causing the growth rings we see in trees.

Xylem is made of nonliving cells and usually carries water from the roots to the leaves, while phloem is made of living tissue and carries sucrose from the leaves, where it is first created as glucose. Glucose is the product of photosynthesis; it is converted to a more stable form of sugar, sucrose, for transport. The sucrose will be shipped to where growth is occurring in the tree or to the roots to be stored as starch.

For years it was believed that sap ran up and down the tree in phloem during the freeze-thaw cycle. Now we know the sap is in the xylem during this time and doesn't move up and down the tree. The sap pretty much stays in place and pressurizes itself every day there is a freeze-thaw cycle. This pressurized sap will drip out of any hole in the tree.

How does it pressurize itself?

During the day, the sap will find the hole of lower pressure (our tap) and drip out until pressure is equalized. At night, cooling and freezing will dissolve carbon dioxide bubbles that were formed during the day, which lowers the pressure of the sap in the xylem; this lower pressure draws in more water from surrounding plant tissue. When the temperature rises above freezing, the carbon dioxide comes out of solution (like opening a shaken pop can), forming bubbles which, combined with the added water, will increase pressure - and the sap will find a low pressure point (our tap) and drip into a collection bag.

Who knew this fantastic food needed all of these things to go right for the sap to flow? Next time I have a pancake or pour some syrup on my ice cream, I'll think about it.

The very curious FDLTCC science tutor Glen Sorenson was Minnesota Teacher of the Year before he retired from teaching science at Proctor High School after 30-plus years. He is an avid outdoorsman who most recently coached the Lumberjacks Nordic ski team.