MAPLE SIRUP PRODUCERS MANUAL 



53 



Figure 8S.— Automatic thermoregulator that compen- 

 sates for changes in barometric pressure. 



firebox and arch to melt the solder and the thin 

 metal of the pans if the pans become dry before 

 the firebox has cooled. 



If water is not available, the fires must be 

 extinguished and evaporation stopped while 

 there is still enough sap in the storage tank to 

 fill the evaporator to a depth of 3 to 5 inches. 



Cleaning the Evaporator 



When maple sap is concentrated to sirup in a 

 flue-type open-pan evaporator, the organic salts 

 become supersaturated; that is, they are con- 

 centrated to a point where they can no longer 

 be held in solution. They are then deposited on 

 the sides and bottom of the evaporator as a 

 precipitate or scale. This scale forms an imper- 

 vious layer that builds up with continued use of 

 the evaporator. The scale reduces heat-transfer 

 efficiency and thus wastes fuel and holds up 

 sirup in the evaporator unduly. 



The scale is of two types. One type is a 

 protein-like material that forms in the flue or 

 sap pans. The other, called sugar-sand scale, 

 forms in the sirup or finishing pan. It is a 

 calcium and magnesium salt deposit similar to 

 milkstone and boiler scale. 



Sugar-sand scale is the more troublesome of 

 the two types. It is esi^ecially troublesome if it 

 is allowed to build up to an appreciable thick- 



ness. Also, sugar sand contains entrapped cara- 

 melized sugar, which contributes to the produc- 

 tion of dark-colored sirup. 



Removing sugar-sand scale is not easy, and 

 doing it by physical means (scraping, scrubbing 

 with steel brushes, or chiseling) is almost im- 

 possible. Removal becomes more difficult as the 

 layer of scale becomes thicker. Clean the evapo- 

 rators often enough to prevent buildup of sugar 

 sand. Teflon-coated pans are easier to clean. 

 Also, keep the underside of the flues clean. 



Mptlioils I'scd ill file Past 



Some methods used in the past to prevent 

 formation of scale and to remove thin layers 

 include — 



(1) Reversing the flow of sap through the 

 evaporator, according to the manufacturer's 

 directions; this retards the formation of scale. 



(2) Running soft spring water through the 

 evaporator for a long period; this tends to 

 dissolve small amounts of scale. 



(3) Pouring skim milk into the pan and letting 

 it remain until it sours; the lactic acid of the 

 sour milk has some solvent action on the scale. 



(.Iieiiiirtil (.le<iners 



Equipment manufacturers have used mu- 

 riatic acid to remove heavy incrustations of 

 sugar-sand scale from evaporators returned to 

 them by maple-sirup producers. This acid is 

 highly corrosive and must be used with gi-eat 

 care to avoid damaging the pans by dissolving 

 the thin tinplate coating. Also, unless a person 

 is experienced in the use of muriatic acid, there 

 is danger that he will get the acid on other 

 materials or on his skin. 



Laboratory and field tests have shown that 

 sulfamic acid (121), one of the chemicals devel- 

 oped for cleaning milk-processing equipment 

 and marine boilers, can be used to remove 

 sugar sand from most maple sirup equipment. 

 Sulfamic acid (the half amide of sulfuric acid) is 

 an odorless, white, crystalline solid and is 

 highly soluble in water. It must not be confused 

 with sulfuric acid. Sulfamic acid crystals can be 

 handled easily, with little risk of spilling and 

 little danger from volatile fumes. As a solid, 

 sulfamic acid is reasonably harmless to the skin 

 and clothing. However, a solution of the acid 

 can irritate the skin. If either the dry acid or its 

 solution comes into contact with the skin, it 



