82 



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



(3) Change the pre filter and the felt filter as 

 often as necessai-y to maintain a rapid rate 

 of filtration. 



(4) When using a finishing pan, filter the partly 

 evaporated sirup before transferring it to 

 the pan. 



(5) If a precipitate forms while the sirup is 

 heating in the finishing pan, the sirup must 

 be given a final or polishing filter. 



(6) Use a closed system in transferring the 

 finished sirup to the holding tank and use 

 an inline, cartridge-type filter for polishing 

 the sirup. 



CHECKJING AND ADJUSTING DENSITY OF SIRUP 



The one specification that all gi-ades of table 

 sirup must meet, irrespective of color or other 

 considerations, is density. The minimum allow- 

 able density of maple sirup is 66 percent by 

 weight of soluble solids (66.0° Brix or 35.6° 

 Baume)*' {130a). This corresponds to 11.025 

 pounds per gallon of 231 cubic inches at 68° F. 



The density of sirup can be measured in 

 three ways: (1) By weight; (2) by refractometry; 

 and (3) by hydrometry. 



Vi <Mght Method 



Determining the density of sirup by the 

 weight per unit of volume is not recommended 

 as a testing procedure for farm use. This test 

 can be made only under- the most exacting 

 conditions and with precision instruments. The 

 gallon measure must have a capacity oi exactly 

 231 cubic inches, the temperature of the sirup 

 must be exactly 68° F., and the weight of the 

 sirup must be determined accurately to within 

 0.01 pound. If any one of these conditions is in 

 error, the measurement is valueless. For exam- 

 ple, an exact gallon of 231 cubic inches of sirup 

 at 68^ F. with a Brix value of 63.5° weighs 10.90 

 pounds {107), whereas the same volume of sirup 

 at the same temperature but with a Brix value 

 of 67.5° weighs 11.10 pounds. Thus, two sirups 

 could differ 4 percent in their solids content and 

 yet differ only 0.2 pound in weight (an amount 

 not detected by ordinary scales) so they would 

 both appear to weigh 11 pounds per gallon. Or 

 an error in weighing of 0.02 pound would cause 

 an error in the solids content of approximately 

 V2 percent (0.5° Brix). For these reasons, the 

 fact that a gallon of minimum density sirup 

 weighs 11 pounds does not mean that this is a 



" Bureau of Standards Baunie scale for sugar solutions, 

 modulus 14.5. 



recommended criterion for measuring the den- 

 sity of sirup. However, it is of great value when 

 used properly and should be used to measure 

 the amount of sirup sold as 1 gallon. 



Since sirup is packed hot in cans that are 

 large enough to allow for the expanded volume 

 of the hot sirup, and since all sirup is not 

 packaged at exactly the same hot temperature, 

 the volume of a gallon of hot, standard-density 

 sirup varies slightly. However, a gallon of 

 standard-density sirup weighs 11 pounds 

 whether it is hot or cold. It is therefore recom- 

 mended that all packaged sirup be weighed 

 before it is sold to determine if the required 

 amount of sirup is in the package — 11 pounds 

 for 1 gallon; 2 pounds, 12 ounces for 1 quart; 

 and 1 pound, 6 ounces for 1 pint. These are net 

 weights and do not include the weight of the 

 can or package. 



Refractometrj' Method 



Determining the density of sirup by measur- 

 ing its refractive index, which changes in a 

 regular manner with changes in the amount of 

 dissolved solids, is the simplest of the three 

 methods. This method is not generally used 

 because it requires a refractometer, an expen- 

 sive optical instrument (fig. 98). However, the 

 precision with which density can be measured 

 with the refractometer makes it well suited for 

 use by Federal and State inspection services, by 

 judges of sirups in competition, and by central 

 evaporator plants. This instrument is not satis- 

 factory for measuring the density of hot sirup 

 (180° F. and above). 



H.vdi-oineti-> Method 



Hydrometry is the most generally used 

 method for measuring the density of cold sirup, ' 



