582 CHAPTER XXVIII 



The advantage of the Coffey still lies in its economy of steam, the in- 

 coming wash being heated by the alcohol and water vapour distilled and 

 i 1 turn condensing this vapour ; actually it consumes only about one-third 

 the steam required for a discontinuous process. Its disadvantages lie in its 

 removing from the product bodies of boiling point remote from that of 

 alcohol and to which the flavour of rum is due ; attempts have been made 

 to restrict the term rum to the product of discontinuous stills. 



Separation of Products of Fermentation. — When using the old forms of 

 vat stills, the bodies that have low boiling point pass over in the first runnings, 

 while the fatty acids and higher alcohols having higher boiling points pass 

 over in the last runnings. Between these comes over the main body of 

 the distillate ; the first and last runnings are collected separately and are 

 called feints or low wines. In the continuous type of still the bodies of low 

 boiling point are found in the cold feints, the fatty acids in the hot feints ; a 

 complete separation is, however, impossible, and all these bodies are found in 

 greater or less degree in the spirit, dependent on the care exercised by the 

 distiller. The boiling points of the principal constituents of rum are in 

 degrees Fahrenheit : — Alcohol 173° ; formic acid 216° ; acetic acid 246° ; 

 butyric acid 315° ; capric acid 380° ; ethyl formate 129° ; ethyl acetate 

 168° ; ethyl butyrate 241° ; ethyl caprate 322° ; formaldehyde 70°. It 

 will be seen that ethyl acetate and alcohol have nearly the same boiling point, 

 so that any ethyl acetate present in the fermented wash will be totally re- 

 covered with the rum. The other bodies will be present in less quantity 

 as their boiling point is more remote from that of alcohol. The majority 

 of these bodies are, however, volatile in steam and hence are present in the 

 distillate in larger quantity than would be supposed from their boiling point. 



Control of the Distillery. — In all molasses distilleries with which the writer 

 is acquainted, the control is limited to the revenue requirements supplemented 

 occasionally by determinations of the reducing sugars in the wash. A record 

 is in this last case obtained of the amount of sugar required to produce 

 a unit of alcohol. This forms a very imperfect control and a tentative 

 more complete scheme is outlined below. 



Fermentation Control. — A composite sample of the wash is collected and 

 in this sample are determined the reducing sugars after inversion expressed 

 as invert sugar ; a second sample is fermented with a pure culture of an 

 approved distillery yeast and in the fermented sample are determined the 

 alcohol and the unfermentable sugars ; deducting the unfermentable sugars 

 from those originally found gives the amount of fermentable sugars originally 

 present ; this quantity should be used in calculating the yield of alcohol per 

 pound of sugar. 



The results obtained on the small scale with pure culture should be 

 compared with those found on the commercial scale, and the deficiency 

 indicates the loss of alcohol due to imperfections in the process of fermenta- 

 tion. 



Distillation Control. — The alcohol in the wash as it enters the still forms 

 the basis of this control ; it should be determined in a composite sample, and 

 compared with the amount actually recovered ; the balance is to be found in 

 the feints, in the lees, and in leaks from the still. The alcohol in these residues 

 should also be determined and all expressed as percentages of that originally 

 present. Finally an account of the alcohol produced per unit of total sugar 

 and of fermentable sugar should be made out. 



