FERMENTATION 585 



Analyses. — The analyses necessary to a distillery control are indicated 

 briefly below. 



Density of Wash. — The methods given for juices in Chapter XXIV are 

 applicable. 



Attenuation. — The attenuation is the difference between the initial and 

 final density, water being put equal to 1000 ; thus wash initially at 1063 and 

 finally at 1015 is said to have attenuated 48 degrees. For each degree of 

 attenuation it is customary to assume the presence of so much proof spirit ; 

 a common allowance is i per cent, of proof spirit for every 5 degrees of 

 attenuation. As the result of a series of laboratory fermentations with pure 

 cultures, the writer found i • 17 per cent, of proof spirit for every 5 degrees 

 of attenuation. This method is not meant as an accurate determination of 

 percentage of proof spirit, but as a guide to revenue and customs authorities. 



Sugars. — ^There is no necessity to determine the cane sugars as such ; the 

 sugars should be determined after inversion following the methods given in 

 Chapter XXV ; as the sugars will be mainly glucose and fructose in approxi- 

 mately equal proportions, it will be best to calculate them as invert sugar. 



Alcohol in Wash and Lees. — Take a definite quantity of material, neutralize 

 with caustic soda, and distil imtil about 90 per cent, of the original volrnne 

 has been collected ; make up with water to original volume and determine 

 the density of the distillate by means of a pycnometer, whence the percentage 

 of alcohol is obtained by reference to the table given below. As lees usually 

 contains very little alcohol it will be well to take a large quantity, say 1000 

 c.c, distil over 500 c.c, re-distil the distillate until 250 c.c. have come over, 

 and finally determine the density of this portion. Otherwise the density 

 of the distillate differs so little from unity that a large percentage error may 

 arise. 



Alternatively, the fractionating still heads of large cooling area, listed by 

 dealers in apparatus, may be used to obtain the alcohol concentrated in a 

 distillate of small volume. 



A form of pycnometer which is of great use in the tropics is that due to 

 Boot, where the bottle containing the liquid is enclosed in a second, the space 

 between them being evacuated. Liquids may be cooled down to 15° C. and 

 kept in the inner bottle without change of temperature and without the 

 condensation of water on the outside of the bottle. 



The table connecting density and percentage of alcohol given below is 

 referred to water at 60° F. In the tropics materials must be cooled down 

 nearly to this temperature ; in the absence of ice this is best done by dis- 

 solving in water a salt such as thiosulphate of soda. Small variations from 

 the standard temperature may be corrected by the use of the expression : — 



/ I — D^\ 



Z) = Di+i 0-00014 + 



150 j 



where D is the required density, D^ the observed density, d the difference in 

 temperature in centigrade degrees between 15-5° C. (60° F.) and that at 

 which the observation was made. 



A table connecting degree Sikes eind specific gravity at 84° F. for strong 

 spirits is added as being useful in certain districts. 



