A hometown newspaper with a local office, local owners & lots of local news
A hometown newspaper with a local office, local owners & lots of local news
Put four of these molecules together and you get tannic acid, a form of tannin. Tannin protects plants, tans leather and stains water. Key for symbols: C (carbon), H (hydrogen), O (oxygen), – (single bond), = (double bond). Molecule drawing by Glen Sorenson/ Pine Knot News
This photo taken by local photographer Mark Cline during last summer's Paddlemania event perfectly illustrates the root-beer-colored water of the St. Louis River caused by tannins.
Merry Christmas to all of you Pine Knotters! Time passes so quickly, 2019 will soon be upon us.
Our last adventure required time travel as we investigated the origin of the red clay that is carried by the Nemadji River.
Our new adventure requires us to get small, but I happen to have a shrinking machine. Miss Frizzle would be proud. This time we are examining the root-beer-colored water of the St. Louis River. This brown-colored water is also common in most of the north shore streams that spill into Lake Superior.
Most of you have probably been told that the brown stain is from tannin that is coming from the bogs and swamps inhabited by spruce trees, tamarack trees, and other bog and swamp loving plants. While that is true, it got me wondering more about what tannin actually is.
Tannin gets its name from the German word "tanna" meaning oak, and/or the Latin word "tannum," which refers to oak bark. Extract taken from oak bark is high in tannin and was used to tan leather in the old days. Plants that pucker your mouth and taste bitter are relatively high in tannin, plants like rhubarb, red grape skins, pomegranates and tea leaves. Bite an acorn or suck on a used tea bag and you will taste tannin.
It is now time to get small and find out what tannin looks like, why it is in plants, where it is in plants, and how it tans animal skin.
As we shrink into the bark of a spruce tree, we will get small enough to observe live cells just under the bark. We see rows and rows of square cells all lined up, forming tubes that run up and down the tree. In these cells are big bubbles called vacuoles: in the vacuoles, I see molecules of tannin - each molecule consists of 12 or 13 hexagonal rings of carbon, all connected by oxygens and hydrogens. Remember that tannin tastes astringent and bitter at the same time, maybe the taste, the smell, or something else in this molecule is what actually repels insects that would consume these trees.
Finally, we will shrink into the protein molecules of a deer hide that has just been put into a vat of tannin (tannic acid). As the molecules approach the collagen fibers in the skin of this deer, we see them react. This reaction kind of coats the collagen, making it more water resistant and less prone to attack by bacteria. The hide has been preserved, if we take care of it.
Tannin does a lot more than just turn the St. Louis River root beer brown.
Have a happy and curiosity-filled new year!
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 also an avid outdoorsman who most recently coached the Lumberjacks Nordic ski team.
