MAPLE SIRUP PRODUCERS MANUAL 



45 



Figure 79. — The float valve on the sap pan adjusts tlie 

 depth of the Uquid in the evaporator. Different devices 

 are used to obtain precise valve settings. 



ORIG, 



BOILING TIME (MINUTES) 



C/iari 5.— Effect of length of boiling period on color forma- 

 tion (color index) in sap of different solids concentra- 

 tions. 



concentrations little color is produced in a given 

 boiling time, whereas at higher concentrations 

 more color is produced. The rate of color forma- 

 tion does not increase appreciably until the 

 Brix value of the sap reaches 25° or more, and 

 this occurs after the sap reaches the sirup pan. 

 To provide a basis for comparing color of 

 maple saps of different concentrations, color is 

 expressed as color index. Color index is meas- 



ured with monochromatic light in a spectropho- 

 tometer: 



86.3% 



Color index = A 



1 cm 



A.,,„ (86.3/6C) 



where A,-,,, is the observed absorbance at 450 

 millimicrons with distilled water used as the 

 blank; b is the depth of the solution in centime- 

 ters; and c is the grams of solids as sucrose per 

 100 milliliters of solution as determined on an 

 Abbe refractometer. The maximum color in- 

 dices for table sirup of various grades are: 0.510 

 for U.S. Grade AA (Light Amber), 0.897 for U.S. 

 Grade A (Medium Amber), and 1.45 for U.S. 

 Gi-ade B (Dark Amber). 



Other changes that occur in the sap as it boils 

 are shown in charts 5 and 6. The rate of color 

 formation is greatest as the sap approaches the 

 concentration of finished sirup (150). Thus, the 

 length of time that sap is heated in the sap pan 

 (when the Brix value is low) is relatively unim- 

 portant in the formation of color. In the sirup 

 pan, however, color develops rapidly as concen- 

 tration increases. 



The rate at which water is removed from sap 

 at different boiling times and the corresponding 

 solids concentration are shown in charts 7 and 

 8. 



The curves show that the average time that a 

 lot of sap with an initial solids content of 2.5° 

 Brix is in the evaporator is approximately IV^ 

 hours — a little less than 30 minutes in the sap 

 pan and slightly more than 60 minutes in the 

 sirup pan. To make high-quality, light-colored 

 sirup, the time required to evaporate the sap to 

 sirup must be kept to a minimum. Conditions 

 that affect the boiling time are: (1) The design 

 of the evaporator; (2) the amount of heat ap- 

 plied to the evaporator; (3) the efficiency of the 

 heat transfer; and (4) the depth of the boiling 

 liquid. Once an evaporator is selected and pur- 

 chased, the sirupmaker controls only the 

 amount and steadiness of heat applied to the 

 pans and the depth of boiling sap. 



Evaporation Time 



The evaporation time is measured from the 

 time a unit of sap enters the sap (flue) pan until 

 it is removed from the sirup pan as sirup. 

 Evaporation time should not be measured until 

 the evaporator is operating steadily, the heat 



