48 



AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



percent of the 33.4 p:allons of water that had to 

 be removed to make 1 gallon of sirup. By the 

 time the solids had increased to only 19° Brix, 90 

 percent of the water had been removed, and the 

 sap had progressed only halfway through the 

 sirup pan. Thus, the remaining 10 percent of the 

 water was removed in the last half of the sirup 

 pan. This shows that most of thf water is evapo- 

 rated while the solids are at sufficiently low con- 

 centrations to have little effect on the color of 

 the sirup. It also shows that sap must be kept 

 moving forward through the pan as it ap- 

 proaches sirup concentration, so that it can be 

 removed from the evaporator as quickly as pos- 

 sible. 



This also explains why adding one or more 

 sap (flue) pans in a series does not increase 

 evaporation time but does increase evaporation 

 rate and capacity. Lengthening the evaporator 

 system by increasing the number of feet that 

 the sap must travel through the different chan- 

 nels makes use of the engineering rule that 

 evaporation (heat transfer) increases as the 

 rate at which the liquid moves over a heated 

 surface increases. Thus, lengthening the evapo- 

 rator by using supplementary flue pans will not 

 increase holdup time; it actually decreases it. 



Therefore, the percentage of solids (weight-vol- 

 ume) of the sirup divided by the Brix value of 

 the sap equals the number of gallons of sap 

 required to produce 1 gallon of sirup. The equa- 

 tion is: 



86 



where a = the numberofgallonsofsap to produce 

 1 gallon of standard-density sirup. 



X = the Brix value of the sap (to represent 

 the solids concentration of the sap). 



Fi"om this number, 1 is subtracted to obtain 

 the number of gallons of water that must be 

 evaporated from the sap to obtain 1 gallon of 

 sirup. The following equation is used: 



86 



Example: With sap having a density of 2.4° 

 Brix, 



S6_ 

 2.4 



1, or 36 - 1 = 35, 



the number of gallons of water that must be 

 evaporated to obtain 1 gallon of standard-den- 

 sity sirup. 



Ride of 86 



The amount of water that must be removed 

 to reduce the sap to sirup varies with the solids 

 concentration of the sap. 



The "Rule of 86" can be applied to determine 

 the number of gallons of a particular sap re- 

 quired to produce 1 gallon of standard-density 

 sirup. The number 86 is used in the calculation 

 as representative of the percentage of solids (as 

 sugar) on a weight-volume basis that is found 

 in a gallon of standard-density sirup. (Until 

 1974 the standard density for maple sirup was 

 65.5° Brix, and sirup of this density contains 

 86.3 percent solids as sugar. Now that the 

 standard density is 66.0° Brix, the percentage of 

 sugar in a gallon of standard sirup is actually 

 87.2, but the traditional "Rule of 86" persists in 

 the industry and is quite satisfactory for practi- 

 cal purposes.) 



Since the solids concentration of sap is com- 

 paratively low, its Brix value and percentage of 

 solids (weight-volume) are essentially the same. 



Suniniaiy 



(1) The modern evaporator is an open-pan, flue 

 type and has a high evaporation efficiency. 



(2) The major changes that affect sirup quality, 

 color, and flavor occur after the sap has 

 been concentrated to 45° Brix. 



(3) The development of color and flavor depend 

 on the length of time sap with a Brix value 

 of 45° or higher is boiled. 



(4) Evaporation rate is increased if the path 

 the sap travels over the heated surfaces is 

 lengthened. 



(5) Use of multiple sap pans assembled in series 

 increases the rate of evaporation. 



(6) The time required for the last stage of 

 evaporation is determined by the holdup 

 time (depth of sap in evaporator, last section 

 or in finishing pan) and the intensity of the 

 heat. 



(7) Pi'oduction of light-colored sirup is favored 

 by shallow depth of sap in the evaporator 

 and by intense constant heat. 



