MAPLE SIRUP PRODUCERS MANUAL 



75 



20 30 40 50 



BRIX (DEGREES) 



Chart 16. — Change in the rate of loss of water by evapora- 

 tion, with constant heat, as the concentration of sap 

 increases. Boiling sap with an initial density of 22° Brix 

 loses 42 grams of water per minute, whereas sirup with 

 a density of 65° loses only 15 grams of water per 

 minute, a threefold decrease in rate. 



Special Theniionietei*s 



In sirupmaking, a knowledge of the boiling 

 point of standard-density sirup in ° F. is impor- 

 tant provided a temperature reference point 

 (the boiling point of water) is established and 

 the correct boiling point of sirup is located 7 

 above it. On this basis, special thermometei's 

 have been developed for use in making sirup: 

 The liquid-stem thermometer with movable tar- 

 get, the liquid-stem industrial thermometer, 

 and the dial thermometer with movable dial. 



Target Tlierntonieter 



The target thermometer does not have any 

 markings on the stem. The degree lines on a 

 movable target refer to the boiling point of 

 water rather than to ° F., as on the conven- 

 tional Fahrenheit thermometei-. 



The target thermometer is calibrated by plac- 

 ing the bulb in either boiling water or boiling 

 sap. The target is moved by means of an adjust- 

 ing screw until the line "water boils" coincides 

 with the top of the mercury column. The line 

 "sirup" is exactly 7° above the line "water 

 boils." This is the boiling point of standard- 

 density sirup for that hour and place. After 

 adjustment, the thermometer is placed in the 

 sirup pan adjacent to the place where the 

 sirup is drawn off. 



Unfortunately, any thermometer set in the 

 evaporator will be surrounded by steam, which 

 makes it difficult to read (fig. 91). 



Use of a flashlight' to illuminate the ther- 

 mometer and a large funnel to divert the steam 

 makes viewing easier. The funnel is held with 

 the tip toward the thermometer, and the ther- 

 mometer is viewed through the funnel with the 

 aid of the flashlight. 



Liqiiitl-Slrm Inthistrial Thcriiiomflfr 



The liquid-stem industrial thermometer does 

 not have special markings or a movable target. 

 But it does have an open scale — a lineal dis- 

 tance of approximately 3 inches for 10° F., 

 which is almost three times that of other ther- 

 mometers (fig. 92). It is calibrated in hU" and has 

 a magnifying device. These features make it 

 ideal for use in sirupmaking. These thermome- 



PN-4787 



Figure 91.— The target thermometer is placed in the 

 boiling sirup. The fine mercury column is difficult to 

 see because of the steam. The boiling sirup being tested 

 must be deep enough to cover the bulb of the thermom- 

 eter. The thermometer must be in boiling sirup and as 

 close to the point of sirup drawoff as possible. 



