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PARTIAL MOLAR VOLUME

Written by Franklin M. Chen, Ph.D.

V

EDITORIAL COMMENTS

Its Application in the

Brewery and Distillery

for Volume Contraction Calculations and

Alcohol Concentration Determination

olume contraction With this paper, brewers and distillers now have access to a third approach for alcohol dilution has been a topic of calculations: the gauging manual method, the Trivagli method as seen in Artisan Spirit and now interest for professionals this partial molar volume approach. If done correctly the partial molar volume approach should and technical staff in the be the most accurate of all based on root thermodynamic principles. The data here are for an brewing and distilling operating temperature of 20 °C. The reader should note that a set of partial molar volume values industry when mixing would need to be calculated for both ethanol and water for each concentration of ethanol to be alcohol solutions of mixed or diluted if a different desired working temperature is used. Once again, however, the different percentages editors believe the tolerances between reporting at 20 °C and 15.56 °C (60 °F) should allow by volume (v/v) (ABV) or extension of the data here to a 60 °F situation. Dr. Chen discussed this approach at different upon mixing of alcohol temperatures in a previous article.3 and water solutions. A recent publication in this magazine presented F I GUR E 1 examples of calculations to account for such volume contractions (sometimes called excess volumes).1 In this article, I present the details for a different approach for calculating volume contraction and provide another confirmation on final alcohol content for those performing required 1.2 alcohol dilutions in their facility. The term partial molar volume refers 1 to a thermodynamic quantity with a strict mathematical definition. In plain English, it 0.8 refers here to the discreet incremental total solution volume changes with the discreet 0.6 incremental increase in the number of moles of alcohol when the number of moles of water is held 0.4 constant. Such a strict mathematical definition ensures that partial molar quantities are 0.2 additive. The proof for this remarkable property can be seen by reference to a physical chemistry 0 textbook.2 It is noted that the presentation 0 20 40 60 80 here deals with a standard temperature of

density (g/mL)

DENSITY DATA from the OIML TABLE (blue) and from UW-GREEN BAY (red)

100

ABW (w/w, alcohol)

80

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# Artisan Spirit: Spring 2017

The magazine for craft distillers and their fans.

# Artisan Spirit: Spring 2017

The magazine for craft distillers and their fans.