Sap's Arising
Northerners always await the first signs of spring--the ducks and geese returning, pasque flowers on a south slope, the warmth of the sun. These all tell that life is returning after the snowy, sparkling winter. One sign of spring that passes unheralded to all but the most die-hard natural history buffs and tree lovers is the almost magical flow of sap in our white-barked birch trees.
Sap flow is the result of so-called root pressure. That is, water is actively absorbed by the root system, but pressure builds because little water is lost from the tree as a whole. Later, the trees leaf out and water-using photosynthesis begins so that the pressure in the roots is relieved.
Birch sap usually begins to flow in late April in interior Alaska and lasts for 10 to 15 days. During the first 5-10 days, the sap is a relatively clear liquid, but as buds begin to break and sap flow decreases the liquid becomes milky in color. This clouding accompanies large increases in the yeast content of the sap.
Sap production varies from tree to tree, and from year to year. Some trees in a stand may produce no sap while others produce 25 gallons or more. Sap collections taken in interior Alaska during 1976 and 1977 showed that some trees were good or poor producers during both years while others were relatively good producers one year and relatively poor the next. Tests have indicated that trees on low-elevation south slopes produce best.
The sugar content of the birch sap (about 1%) is low compared to that of maple sap (2.5%) from which syrup is made. Furthermore, sucrose (ordinary sugar) makes up only 18% of birch sap whereas 99% of maple sap is sucrose. Fructose and glucose (honey sugar) are the main sugars in birch sap.
Some people have a special motive for watching for the first sap of spring. They use it to make beer, wine or syrup. In the Ukraine region of Russia sap from several species of birch is collected on a large scale (2,000 metric tons in 1970) and used to make wine, soft drinks and health aids.
Birch sap can be used as it comes from the tree or it can be boiled to concentrate it. Probably the most sophisticated sap processing setup in the Fairbanks area is that of Mr. Carroll Phillips who has been collecting and processing sap since about 1968. Mr. Phillips currently taps about 400 trees to obtain 2,000-3,000 gallons of raw sap. He boils the sap using steam produced in a wood-fired boiler which was brought into Fairbanks in the early 1900's. The process has two steps; during the first, a batch of 70 gallons of sap is reduced to about 3 gallons in 1-1/2 to 2 hours. Secondly, the concentrated sap is placed in a steam kettle and further reduced to 1 gallon of syrup.
Obviously few people have this system available to them. The most common procedure is to boil the sap on the kitchen stove or a wood stove in the back yard. Using this method, it's not possible to concentrate to the degree attainable with the steam kettle without burning the remaining material. After boiling, corn syrup is sometimes added to improve the consistency of the end product.
If you are interested in celebrating the rites of spring by collecting sap for your own use, the following steps will prove successful: 1) Drill a 4-6 cm deep hole in a birch with a hand auger. 2) Fashion a spout from aluminum and insert in the hole. 3) Hang a bucket below the spout to catch the sap as it drips from the tree. Only the clear sap that is produced early in the period is generally used for making syrup, wine or beer.
