December 5th, 2008 | 
Author: Sap is made into syrup by boiling off water, which increases the sugar content to 66 percent and causes chemical changes that darken the syrup and provide its characteristic taste. The amount of sap required to produce a gallon of syrup depends on the sugar content of the sap. On the average, in Ohio, sap averages about two percent sugar content, requiring 43 gallons of sap to produce a gallon of finished syrup. If the sap sugar content is higher (it varies from tree to tree, with weather, and other factors), less sap will be needed to make a gallon of syrup; if lower, more sap will be required.
Most large commercial producers use a continuous feed evaporation process to make syrup. An evaporation pan is designed so that sap is added to the pan at one end and syrup is removed at the other in a “continuous” process. Most hobbyists use a “batch” approach, in which sap is placed in a pan and heated. More sap is added as water evaporates until a suitable amount of concentrated sap is present. The evaporation process is then continued with no additional sap and the entire batch is “finished” to the desired density. To batch-process syrup, a large pan, such as a roaster (teflon coated pans are ideal), is needed. The pan should be at least 6 inches and preferably 8 inches deep to prevent foaming over.
Rates of evaporation from a flat bottom pan are highly variable. Depending on many factors, including the size of the heat source and the type, size, and construction of the pan, they may range from as little as 3/4 to more than 1-1/2 gallons of water for each square foot of liquid surface. A 12-inch square or 14 inch in diameter circular pan both have one square foot of liquid surface. Remember, 43 gallons of sap are required to produce one gallon of syrup — 42 gallons of water must be evaporated. It will normally require somewhere between 28 and 56 hours of continuous boiling (and sap refilling) if a pan with one square foot of liquid surface is used. By comparison, a gallon of syrup can be produced in between 9 and 18 hours using a rectangular 24″ x 18″ pan (3 square feet of liquid surface). Obviously, the larger the pan, the more quickly the evaporation process will be completed.
Do not fill the pan completely, as boiling sap usually rolls and foams. Remember to boil outside the house or at least vent the steam outside. Bring the sap to a boil. If foaming occurs, skim the foam off and discard. Maple producers use a defoamer to reduce the amount of foaming. Defoamers are not, however, commonly used when batch processing small amounts of sap. If foaming over is a problem, the common solution is to use a deeper container. If needed, commercial defoamers are available from maple equipment suppliers or a flavorless vegetable oil may be used. Use the defoamer sparingly (a small drop at a time) as excessive amounts may give the syrup an off-flavor.
Continually replace the sap as evaporation occurs. To avoid burning or scorching, monitor the heat carefully (don’t let the heat get too high), and keep at least 1-1/2 inches of liquid in the pan. The risk of scorching increases as the density of the liquid increases.
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