72 



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



Table 12. — Boiling temperature above that for 

 water for solutions of different concentrations 

 of sugar 



Thus, the thicker the sirup, the better it tastes. 

 However, sirup with a density of more than 67° 

 Brix crystallizes on storage at room tempera- 

 ture; 67° Brix, therefore, becomes the upper 

 permissible density. 



EfTect orTemiMM-atiiiT on N iscosily 



As the temperature of a sugar solution in- 

 creases, its viscosity drops sharply. Standard- 

 density sirup at its boiling point has a viscosity 

 of about 6 centipoises, which is only one.thir- 

 tieth that of sirup at room temperature; that is 

 why sirup filters so much better when it is at or 

 near its boiling point. Likewise, the viscosity of 

 boiling sirup with a density between 50° and 60° 

 Brix is approximately one-half that of stand- 

 ard-density sirup; and that is why it is advanta- 



geous to filter sirup just before it is transferred 

 to a finishing pan, when its density is approxi- 

 mately 60° Brix or less. 



This lowering of the density by heating sirup 

 explains why hot sirup, even though it is of 

 standard density, tastes thin and watery. 



Old Stan(iar<l»; <)f FinLshed .Sirup 



In the past, the finishing point of sirup was 

 determined by a number of methods. None of 

 these methods was precise, and their skillful 

 use was an art. For that reason, comparatively 

 few men won the enviable title of "sugar- 

 maker." 



Typical of these methods was the "blow" test. 

 In this test, a small loop of wire was dipped into 

 the boiling sap. When the film that formed 

 across the loop required a certain puff of breath 

 to blow it off, the sirup was considered finished. 

 Another method more commonly used was the 

 "apron" test. In this test, a scoop was dipped 

 into the boiling sap and then held in an upright 

 position to drain. Formation of a large, thin 

 sheet or apron with the right shajDe and other 

 characteristics indicated that the sirup was 

 finished. 



L M- ol' \*vvvisiou lii.sti-iini('iil!< 



Precision instruments are now available by 

 which the finishing point of sirup can be deter- 

 mined easily and with a high degi-ee of accu- 

 racy. As concentration progresses, there is a 

 progressive increase in the boiling point, in 

 density, and in refractive index. These can be 

 measured accurately and precisely with a ther- 

 mometer, a hydrometer, and a refractometer, 

 respectively. However, only the elevation of the 

 boiling point is applicable to a sugar-water 

 solution, such as sap, while it is actively boiling. 



Kl^'^alion ol' B4Mliii<>: I'oinI 



Chart 15 and table 12 show the changes in 

 boiling-point temperature for sugar solutions at 

 different concentrations. When a sugar solution 

 has been evaporated to the concentration of 

 standard-density sirup (66.0° percent of sugar, 

 or 66.0° Brix), its boiling point has been ele- 

 vated 7.1° F. above the boiling point of water. 

 Between 0° and 2T Brix, there is only a slight 



