THE EFFICIENT (RUM) DISTILLER THE NEED FOR HEAT TO BOIL ALCOHOL Heating a water-alcohol solution, such as the one obtained at the end of fermentation, allows for the alcohol to be evaporated, separated and concentrated. The evaporation part is easy to understand, even for those with only superficial knowledge of this industry, but the details of how the evaporation works can be a bit trickier to understand. Take for example, the following table1:
% of alcohol in the boiling liquid
Temperature needed to boil alcohol (F)
Temperature needed to boil alcohol (C)
% of alcohol in the condensed vapor
PART II WRITTEN BY L U I S K . AY A L A
I N PA RT I O F T H I S S E R I E S W E E X P L O R E D THE STOICHIOMETRIC AND ACTUAL YIELDS O F A L C O H O L T H AT C A N B E O B TA I N E D F R O M FERMENTING SUGARCANE. PRODUCING THE LARGEST POSSIBLE AMOUNT OF ALCOHOL D U R I N G F E R M E N TAT I O N , H O W E V E R , I S O N LY A P A R T I A L V I C T O R Y: W E M U S T E F F I C I E N T LY A N D T H O R O U G H LY C O N C E N T R AT E T H AT A L C O H O L T H R O U G H D I S T I L L AT I O N B E F O R E WE CAN ENJOY THE FRUITS OF OUR LABOR. A N D W H I L E P A R T I WA S R U M - C E N T R I C , P A R T I I A P P L I E S W I D E LY T O A L C O H O L S O B TA I N E D F R O M A L L F E R M E N TA B L E S O U R C E S .
The first, leftmost column, indicates the percentage of alcohol (ethanol, in this example) present in the fermented wash. Columns two and three indicate the temperature — in degrees Fahrenheit and Celsius respectively — needed for the amount of alcohol in the first column to become volatile. The fourth, rightmost column indicates the alcohol strength at which the condensed vapor will be. The table seems straightforward, but hidden within are several key pieces of knowledge, some more obvious than others: 1. As the amount of alcohol in the fermented wash approaches zero, the temperature required to boil it approaches the temperature required to bring water to a boil (212 F/100 C). 2. Conversely, the higher the alcohol volume in the liquid, the less temperature is needed to make that alcohol volatile. 3. The alcohol concentration of the vapors produced is much higher than the concentration of the alcohol in the starting liquid. If this wasn’t the case, the resulting distillate would have the same strength as the starting wash, which would defeat the purpose of distilling. 4. The difference between the alcohol concentration in the liquid and in the vapor is larger with lower ABVs, but tends to diminish as we exceed 90% ABV. The chart shows only the boiling points and concentrations for ethanol, which is the heart of the distillation and the heart of our business. Each type of congener (alcohol and volatile substance) in the wash will have its own chart, with its own set of volatile temperatures and concentrations. Those more volatile than ethanol are collectively known as heads, while those less volatile than ethanol are collectively known as tails. 1 Source: The Rum University, “The Art of Rum Making”
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