Volumes of Alcohol and Water” and associated instructions.) The issue was raised in 2015 at a distillers’ conference where it became clear that some distillers were not actually doing proofing for TTB reporting purposes, potentially opening themselves up for fines or forced closure of their operations. More than 10 years ago our laboratory updated and extended those earlier published Alcohol Dilution tables - (Reduction Table for Dilution of Alcohol to Lower Strength – see Figure 1) and provided an example of how to get dilution water volumes to reduce the strength of spirit samples using the Gauging manual data. The table can be found here:
alcbevtesting.com/wp-content/uploads/2009/05/NewCopyDilutionTable.pdf However, the table covered only specific pairs of data (e.g. dilution from 95% ABV to 85%, 80% etc., in 5% increments). Only smaller volume reductions are called for in practice making the table helpful but not useful for daily operations. To do this type of process the distiller is still required to look up U.S. Government Gauging Manual Tables and then run detailed calculations to derive their reduction volume water values. The Gauging tables can be found here: www.ttb.gov/foia/gauging_manual_toc.shtml for those interested in the traditional method. Recently we revisited the calculation process for this kind of table and noted that the approaches outlined below can provide confirmation of our results.
ALCOHOL DILUTION CALCULATIONS Now we attend to some useful formulas dealing with alcohol dilution factors, with the theory presented largely by Travagli. Note these calculations work very well with hydroalcoholic solutions and with traditional spirits. The more modern spirits and liqueurs with heavy flavorings, oils, sugars, etc., require more attention to detail. For official alcohol content values needed for legal approval, we recommend distillers send in such samples to a fully qualified testing laboratory unless they wish to invest heavily in instrumentation. The instruments needed include, but are not limited to: an analytical laboratory balance, distillation systems, temperature regulated water baths and digital density meters or GC systems for the analysis. Even then, there can be issues with codistilling congeners and oils, etc. Such issues are often ignored or forgotten about only to return painfully when regulators reject the products for failing to meet specifications. The major point to mention is that these alcohol and water dilutions are not easy to do accurately and effectively due to the aforementioned non-volume additive nature of water and alcohol mixtures. Volume contraction was noted as about 3%, so the contraction issue cannot be neglected when dealing with alcohol beverage formulations (ref. Travagli and see Addendum for details especially with respect to the ethanol “contraction curve” and a range of contraction values). Also due to volume expansion and contraction effects caused by temperature dependency, the use of mass rather than volume relationships make it more accurate in practice to obtain the subsequent alcohol by volume values. As Travagli rightly points out, the classical formula for mixing
solutions does not hold true here.
aVwater + bValcohol ≠ (a+b)Vmix Where a and b represent the units of volume respectively.
DETERMINATION OF THE ALCOHOL CONCENTRATION OF AN ALCOHOL AND WATER MIXTURE Travagli discusses some theory of additivity of alcohol and water but, most importantly, presents a useful equation dealing with the combination of equal volumes of water and alcohol. Here we see the need to use density values as well as volumes. For reference, the legal metrology tables known as the OIML tables can be consulted for the density and the corresponding alcohol values and are available online: www.oiml.org/en/files/pdf_r/r022-e75.pdf/view. Table Va. refers to density and alcohol by weight (ABW) values and Table Vb. refers to density vs. alcohol by volume (ABV). Thus we see from this work: EQUATIO N1
% w/w diluted = % w/w conc. ×
ρ conc. × V
ρ conc. × V + ρ water × V
Where ρ = density (of the stock concentrated alcohol and water respectively) When equal volumes of water and alcohol are used the V terms can be deleted: EQUATIO N2
% w/w diluted = % w/w conc. ×
ρ conc. + ρ water
For example, we can start with a 95% by volume alcohol (v/v) solution (ABV). The first step is to obtain the corresponding alcohol density from the OIML tables (density vs. ABV values) which gives 0.8114 g/mL as the density (20 °C) for 95% ABV stock. The OIML density for 95% ABV (at 20 °C) corresponds to a value of 92.41% alcohol by weight (ABW). The density for water, under defined conditions and as commonly used in practice, is 0.998203 g/ mL (see Eq. 1). Density values and theory are more involved than this, but for simplicity, the above notations are sufficient for our arguments. The OIML tables present values at 20 °C, though values for 60 °F (15.56 °C) are used in the U.S. for proofing purposes. As the Gauging manuals and U.S. regulations rely on 60 °F as the temperature of reference, some argue that it is the ONLY approach to take in the U.S. Within the normally allowed degrees of tolerance, data for alcohol and density as expressed at 20 °C should, hopefully, become acceptable in practice for alcohol dilutions. Those experienced with the Gauging manual approaches can test out the equations presented here to see how good a fit they really are. They should crosscheck very well! A major point to note is the need to be careful with any approaches to this topic. With
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