During a temperature increase, volume of alcohols expands or conversely, during a temperature decrease, the volume contracts. The higher the alcohol content, the more pronounced this phenomenon becomes.

In the field of spirits, during production, for inventory management and bulk transactions, the measured volume can vary significantly due to temperature fluctuations. Therefore, to calculate the volume of pure alcohol, it is essential to convert the measured volumes to 20°C.

So how to calculate the volume at 20°C ?

The factor of contraction or expansion of a volume of alcohol which will make it possible to calculate the volume at 20°C is called:**Correction factor “Cf”**

**Volume at 20°C = Volume at temperature * Correction factor**

This correction factor depends not only on the temperature of the product (T°C) but also on its **A**lcoholic **S**trength by **V**olume, expressed as a percentage volume at 20°C (A.S.V. % vol.)

**Cf = f (A.S.V. % vol. at 20°C, T°C)**

**There are 2 methods to convert at 20°C, alcohol volume measured at another temperature **

1) First method: Used tables to find the Correction factor (Cf)

Some tables and in particular the most used in Europe: The “Practical Guide to Alcoholometry” (1) or the “Practical Alcoholometric Tables” (2) provide this information.

In these tables, Cf is indicated for each Alcoholic Strength by Volume (A.S.V.), measured with an alcoholometer at the same temperature as the product, in steps of 1% vol. and at each temperature, in steps of 1°C.

For intermediate values of A.S.V. and temperature, the Practical Guide to Alcoholometry, specifies that it is the factor of the lowest alcohol level which must be taken into account and that it is the linear interpolation which must be made, from the 2 values framing at +/- 0.5°C, the temperature (3).

There is no specific recommendation in the “Practical Tables of Alcoholometry”.

**There are 3 methods for the use of these tables**

- 1st case: volume and A.S.V. are made simultaneously and the A.S.V. is expressed at the same temperature as that obtained when measuring the volume.
- 2nd case: A.S.V. is already given at 20°C
- 3rd case: A.S.V. is measured or expressed at a temperature other than that obtained for the volume measurement.

For each case, here is examples of using the Practical Guide to Alcoholometry to find the correction factor.

**1st case: T****he measurement of the A.S.V. was made and expressed at the same temperature as the volume measurement of the product**

For a measurement with an alcoholometer of 66.5% vol. at 12.5°C and a volume of 10 HL measured at the same temperature,

A.S.V. to be taken into account in table VIIIb (white pages) of the Alcoholometry Guide to find Fc is therefore 66% vol.

At 66% vol. and 12°C, Fc indicated in the 1st column of the Guide is 1007. At 66% vol. and 13°C it is 1006.

The extrapolation rule recommended in the Practical Guide to Alcoholometry leads to a correction factor of 1006.5 (average of 1007 and 1006).

**2nd case: A.S.V. is already given at 20°C**

When measuring alcohol content with an electronic densimeter this one gives directly the A.S.V. in % vol. at 20°C. With the White Pages of the Practical Guide to Alcoholometry, position yourself at the volume measurement temperature line and look for the A.S.V. converted at 20°C.

The correction factor can be read in the 1st column on this same line.**Example:** If in the previous case, the measurement of the A.S.V. had been measure with the electronic densimeter, this would have directly measured 69% vol. at 20°C. For the volume measurement temperature at 12.5°C, 69% vol. will be found at the intersection of 66.5% vol. and 12.5°C, i.e. Fc in the 1st column of 1006.5 (average of 1007 and 1006).

**3rd case: The measurement of A.S.V. was not made nor expressed at the same temperature as the volume measurement of the product**

In this case, it is necessary to start by converting the A.S.V. measured at 20°C and look up the volume correction factor as shown in case 2.

The extrapolation method between 2 temperature steps (1°C), as indicated in the Practical Guide to Alcoholometry (3), is not the correct method. The following paragraph presents the official calculation of the volume correction factor and shows an example of the deviation generated during an extrapolation conducted according to the recommendation of the Alcoholometry Guide.

2) 2nd method: Calculation of the Correction factor with official table

For an alcohol, the variation in density depends on the temperature and the alcohol content. Only the volume expands or contracts, the mass does not vary. It is this mass conservation rule that makes it possible to calculate the volume correction factor (Cf).

The volume Correction Factor (Cf) is in fact the ratio between the density measured at a given temperature and the density at 20°C. These densities depend on the A.S.V. at 20°C.

**Cf = V.M. _{t} / V.M. _{20°C}**

To find the densities, depending on the temperature and A.S.V., a European Directive (4) and French Regulations (5) require reference to Recommendation R022 of the International Organization of Legal Metrology (O.I.M.L.) (6).

The official table which gives the variation in density of a hydroalcoholic mixture according to the A.S.V. and the temperature is reproduced in Appendix 1 of Recommendation R022-f75. See Table No. II of this recommendation (6)

Let’s go back to the example of case 1 by applying the official calculation:

Either a measurement with the A.S.V. of 66.5% vol. at 12.5°C and a volume of 10 HL measured at the same temperature,

the white pages of the Alcoholometry Guide indicate A.S.V. at 20°C of 69% vol.

For this alcohol level, Table II of the O.I.M.L. noted:

**at 12°C**, the volumic mass (g/l) is**894.59****at 13°C,**the volumic mass (g/l) is**893.78**, either an extrapolation to**12. 5****°C**of the average of the 2 previous values:**V.M. t =****894.185****at 20°C**, the volumic mass (g/l) is 888.03**(V.M.**_{20°C})

Calculation of the Correction factor (Cf): **V.M.t (**894.185) / **V.M. _{20°C}** (888.03) =

**1006.9**.

In the 1st case, with the first method given by the Alcohometric Guide, the Cf was** 1006.5**.

**In this example, the difference between the calculation with the officiel table and the method given by the Alcohometric Guide is 0.04%. That is 0.04 HL for 100 HL.**

**To convert volume at 20°C, for more precision on the Correction factor, it’s better to use the calculation with the official method.**

To make calculations easier and more reliable, Labox Boxettes offer automated conversions.

These conversions are performed in accordance with Table II of Appendix 1 of O.I.M.L Recommendation R022-f75, the official density conversion table.

They are made with 2 decimals in % vol. for A.S.V. and with an additional decimal for the correction factor, compared to the Alcoholometry Guide

**Evelyne CHANSON – Quality Control Wines and Spirits Consultant at EC Consulting**

*1) Alcomometry Practical Guide – P. OUDIN*

*2) Practical alcohol tables – Volume 1 – Commission of the European Communities*

*3) Alcomometry Practical Guide, chapter II “Etudes des tables alcoométriques pratiques” A. Exemple 2.*

*4) European Directive 2011/17/UE of 03/09/11*

*5) French decree 79/200 of 03/11/79 *

*6) Recommandation R022-f75 from O.I.M.L – 1973, Annex 1, Table II.*

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