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Alcohol Dilution Practices for Distillers: Two Approaches

Gary Spedding,

Brewing and Distilling Analytical Services, LLC

www.alcbevtesting.com info@alcbevtesting.com

Abstract.

Distillers, and those dealing with industrial ethanol in large quantities, are often required to

make dilutions to lower the alcoholic strength of their products. Many solutions can simply be

mixed in appropriate volumes to yield the desired (additivity) ending concentration. However,

some chemicals, ethanol included, when mixed with other aqueous solvents result in a final

solution of lower volume than indicated by their numerically additive values. Many chemists,

mathematicians and distillers still use simple algebraic formulations of the type V1 x C1 = V2 x C2

for hydroalcoholic solution formulations. [V = volume in any unit and C = concentration often %

v/v for alcohol solutions.] However, due to the contraction effect (approx. 3%) upon mixing

water and alcohol the above relationship and algebraically solving for the final concentration is

inadequate for accurate mixing purposes with respect to ethanol and water mixtures including

traditional distilled spirits. Taking the mass relationships of ethanol into account (and

appropriate density data) calculations can be made to solve for alcohol volume strength

reduction. Alternately, tables of data (water volumes to add to a defined volume of alcohol) exist

often in defined % alcohol or Proof reduction increments, leaving the chemist or distiller to

interpolate data for actual or desired conditions. Those tables were generated via

experimentation and the data can be derived by equations based on US Gauging manual tables.

These are known as the “TTB proofing tables”. Calculations using the water and ethanol volumes

for defined mixtures can be done so the dilution tables can be avoided, this is especially useful

when defined increments of strength reduction are needed and those defined changes are not

illustrated in the actual dilution tables. Two main approaches will be presented here. The bulk of

the topic being covered in a forthcoming paper from our laboratory.

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Introduction.

Many years back several publications (The “Art of Distilling” type treatises – of which many have

recently been republished as useful historical documents) discussed alcohol blending and alcohol

dilution issues especially for distillers. Tables (limited in scope) showed a few data points

(volumes of water to add to various strengths of alcohol) leading to correct dilutions of distilled

spirits. A typical example table is shown in Figure 1.

Figure 1: Example Alcohol Dilution Table

Distillers and regulatory agencies provided details dealing with Proofing, Proof Gallon equations

etc., to adequately report alcohol content for excise purposes. Such instructions to be found

online at the US TTB website for example are often difficult to follow and/or provided without

adequate instruction or examples (Example: US Govt. Gauging Manual table 6 “Respective

Volumes of Alcohol and Water” – a portion shown in Figure 2).

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Figure 2: US Gauging Manual Table 6 Quantities of alcohol and water contained in

defined Proof alcohol water mixtures.

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It is to be noted that in Figure 1 the dilution table covered only discreet pairs of data (e.g.,

dilution from 95% ABV to 85%, 80% etc., in 5% increments) and often only smaller volume

reductions are called for in practice. To do this type process the distiller is still required to look up

US Government Gauging Manual Tables and then run detailed calculations to derive their

reduction volume water values {The Gauging tables can be found here:

http://www.ttb.gov/foia/gauging_manual_toc.shtml for those interested in doing it the older

way. – See portion in Figure 2.} An example calculation appears below (Part II).

Part I. Calculating the amount of water needed to dilute a given volume of

alcohol to a lower percentage.

The first approach we cover for those wishing to dilute matured spirits to bottling strength

(proofing) is as follows. 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 also available on line:

{https://www.oiml.org/en/files/pdf_r/r022-e75.pdf/view }. Table Va. referring to density and

alcohol by weight (ABW) values and Table Vb. referring to density vs. alcohol by volume (ABV).

As noted above, tables exist showing the amount of water to add to a given volume of alcohol of

specific concentration to obtain a desired final lower concentration. This is illustrated below.

Now an equation and data from the OIML tables can be used in another approach. For water of

dilution additions, or to prepare solutions of known final volume, the volume of the

concentrated alcohol can be set as 100 parts. From here it is easy to determine the volume units

of water to add.

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Taking this equation:

dilutevv

concdilutevvdiluteconcvvwatery

/

//

%%%

100ρρ ×−×

×=

Or the simplified variant:

−××= concdilute

dilutevv

concvvwatery ρρ

/

/

%%

100

Where:

ywater: The amount of water (volume or units) needed to be added to 100 volumes (or units) of

the higher strength alcohol solution needed to be diluted.

% v/v conc: The ABV % of the high strength alcohol.

% v/v dilute: The ABV % of the desired final (diluted) strength alcohol solution.

ρ dilute and ρ conc: The densities of the respective dilute and concentrated alcohol solutions.

[Obtained from looking up the OIML Density vs ABV tables.]

Looking at diluting 95% ABV alcohol to a 40% ABV strength. We look up the density for each

strength of alcohol finding from the OIML tables 0.8114 (g/mL) and 0.9481 (g/mL) respectively.

Plugging the requisite values into the equations leads to a value for ywater of 144 units (mL, Liters,

100 Liters, or Gallons etc.) of water to be added to 100 units of 95% alcohol. Taking a look at the

Figure (Fig. 1) shows that for diluting 95% ABV alcohol solution to 40% ABV the result agrees

here; the Table in Fig. 1 shows 144 parts water to add to 100 parts of 95% ABV solution. Part II

discusses this further. The use of such equations and the OIML tables will assist in defining

precise dilutions for the distiller.

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Part II. Diluting according to Gauging Manual Table Data and Instructions.

Looking at Figure 1 – this shows the volumes of water to add to 100 units of ethanol to yield the

lower desired strength. Those values are derived by using data generated over a 100 years ago,

whereby, based on Proof (2 x ABV at 60 °F), defined amounts of water by volume and of alcohol

by volume were noted for different proof strength alcohol/water mixtures.

An example will serve to illustrate this. Taking again the situation above whereby we wish to

dilute 95% ABV solution to 40% ABV.

In steps (noting instructions can also be found at the US TTB website under the Gauging Manual

heading):

1. The 95% and the 40 ABV need to be converted to Proof values (x 2) = 190 and 80 Proof

respectively.

2. Look up the volumes of water and alcohol contained in 190 Proof of spirit (see Figure 2 from

the Gauging Manual Table 6). Ethanol is seen to be the original ABV value 95 (volumes) and

Water represents 6.18 volumes.

3. Look up the volumes of water and alcohol contained in 80 Proof of spirit (see Figure 3: a

portion from the Gauging Manual Table 6). Ethanol is seen to be the original ABV value 40

(volumes) and Water now represents 63.42 volumes.

Figure 3: Portion US Gauging Manual Table 6 showing 80 Proof alcohol

composition: ethanol and water.

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4. Take the ratio of the high to low ABV: 95/40 = 2.375.

5. This ratio is multiplied by the volume value of the water contained in the low strength alcohol

mix – (the desired 40% here). 2.375 x 63.42 volumes = 150.62.

6. Finally the water volume value for the high strength alcohol (the 95% ABV solution here) needs

to be subtracted from the value obtained in step 5. 150. 62 - 6.18 volumes (see step 2) = 144.4.

NOW 144.4 VOLUMES (or Units) OF WATER NEEDS TO BE ADDED TO 100 VOLUMES (or UNITS)

of 95% ETHANOL TO OBTAIN the DESIRED 40% ABV SOLUTION.

This agrees well with the approach above (144 Units) for these type dilution processes (Part I).

In regards to the Table (in Fig. 1) it is noted that the data are based on 60 °F (15.56 °C) from

earlier derived Proof Gauging data and that the equations and OIML tables discussed here are

essentially based on 20 °C evaluations. In the US, proof refers to 2 x ABV (%) as determined at 60

°F (15.56°C). There is only a slight difference in the alcohol by volume values at 60 °F vs. 20 °C but

the reader should be aware of this too when making process adjustments in their facility. For

further details on the conversion of alcohol volume values from 20 °C to 60 °F consult with the

team at BDAS, LLC or other qualified distilling consultants. The table in Figure 1 shows only 144

mL and not 144.4 mL water for dilution. Based on a number of variables (not discussed here)

including rounding up this slight discrepancy is fully acceptable and should not affect final mixes

for proofing for records and bottling purposes.

Conclusions.

Using either of the two approaches above should prove useful in standard distillation practice. If

using TTB proofing tables and calculations (or the “standard” Alcohol Dilution Tables – such as in

Fig. 1), as in Part II - the use of the equations here (in Part I) will provide a further means to check

the obtained data. Furthermore, if standard tables such as the one provided as Figure 1 don’t

have the paired values needed for a specific dilution condition, then the equation forms in Part I

and OIML tables (or other suitable tables of alcohol and density values) should provide a quick

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means to solving the dilution factors needed in most proofing and alcoholic strength reduction

situations.

Finally a much more in-depth review of calculations, and the background theory, for reducing the

strength of alcohol, solutions is forthcoming in a paper from our laboratory and slated to be in

the next issue of Artisan Spirit magazine.

Gary Spedding. January 12, 2016. Comments or discussion of errors or omissions to

gspedding@alcbevtesting.com please.