ANNEXU.K.
I.DETERMINATION OF ALCOHOLIC STRENGTH BY VOLUME OF SPIRIT DRINKSU.K.
IntroductionU.K.
The reference method includes two Appendices:
:
Preparation of distillate
:
Measurement of density of distillate
1.ScopeU.K.
The method is suitable for the determination of the real alcoholic strength by volume of spirit drinks.
2.Normative ReferencesU.K.
ISO 3696:1987: Water for analytical laboratory use — Specifications and test methods.
3.Terms and DefinitionsU.K.
3.1. Reference temperature: U.K.
The reference temperature for the determination of alcoholic strength by volume, density and specific gravity of spirit drinks is 20 °C.
Note 1:U.K.
The term ‘at t °C’ is reserved for all determinations (of density or alcoholic strength by volume) expressed at a temperature other than the reference temperature of 20 °C.U.K.
3.2. Density: U.K.
The density is the mass per unit volume in vacuo of spirit drinks at 20 °C. It is expressed in kilograms per cubic metre and its symbol is ρ20 °C or ρ20.
3.3. Specific gravity: U.K.
The specific gravity is the ratio, expressed as a decimal number, of the density of spirit drinks at 20 °C to the density of water at the same temperature. It is denoted by the symbol d20 °C/20 °C or d20/20, or simply d when there is no possibility of confusion. The characteristic that was measured must be specified on the assay certificate using the above-defined symbols only.
Note 2:U.K.
It is possible to obtain the specific gravity from the density ρ20 at 20 °C: 
3.4. Real alcoholic strength by volume: U.K.
The real alcoholic strength by volume of spirit drinks is equal to the number of litres of ethyl alcohol contained in 100 l of a water-alcohol mixture having the same density as the alcohol or spirit after distillation. The reference values for alcoholic strength by volume (% vol) at 20 °C versus density at 20 °C for different water-alcohol mixtures that are to be used are those given in the international table adopted by the International Legal Metrology Organisation in its Recommendation No 22.
The general equation relating the alcoholic strength by volume and density of a water-alcohol mixture at a given temperature is given on page 40 in Chapter 3 ‘Alcoholic strength by volume’ of the Annex to Commission Regulation (EEC) No 2676/90 (OJ L 272, 3.10.1990, p. 1) or in the manual of analysis methods of the OIV (1994) (p. 17).
Note 3:U.K.
For liqueurs and crèmes for which it is very difficult to measure volume accurately the sample must be weighed and the alcoholic strength is calculated first by mass.U.K.
where
=
alcoholic strength by mass,
=
789,24 kg/m3
4.PrincipleU.K.
Following distillation, the alcoholic strength by volume of the distillate is determined by pycnometry, electronic densimetry, or densimetry using a hydrostatic balance.
APPENDIX I: PREPARATION OF DISTILLATEU.K.
1.ScopeU.K.
The method is suitable for the preparation of distillates to be used to determine the real alcoholic strength by volume of spirit drinks.
2.PrincipleU.K.
The spirits are distilled to separate the ethyl alcohol and other volatile compounds from the extractive matter (substances which do not distil).
3.Reagents and MaterialsU.K.
3.1.Anti-bumping granules.U.K.
3.2.Concentrated antifoam emulsion (for crème liqueurs).U.K.
4.Apparatus and equipmentU.K.
Usual laboratory apparatus and in particular the following.
Water bath capable of being maintained at 10 °C to 15 °C.
Water bath capable of being maintained at 20 °C (± 0,2 °C).
Class A volumetric flasks, 100 ml and 200 ml, that have been certified to 0,1 % and 0,15 % respectively.
Distillation apparatus:
General requirementsU.K.
The distillation apparatus must meet the following specifications:
the number of joints must be no more than the strict minimum needed to ensure the system is leak-tight,
inclusion of a device designed to prevent priming (entrainment of the boiling liquid by the vapour) and to regularise the distillation rate of alcohol-rich vapours,
rapid and complete condensation of the alcohol vapours,
collection of the first distillation fractions in an aqueous medium.
The heat source must be used with a suitable heat-diffuser to prevent any pyrogenic reaction involving the extractive matter.
An example of a suitable distillation apparatus is shown in Figure 1 and includes the following parts:
round-bottomed flask, 1 litre, with a standardised ground-glass joint,
rectifying column at least 20-cm high (a Vigreux column, for example),
elbow connector with an approximately 10-cm-long straight-rimmed condenser (a West-type condenser) fitted vertically,
cooling coil, 40-cm long,
drawn-out tube, taking the distillate to the bottom of a graduated collecting flask containing a small amount of water.
Note:U.K.
The apparatus described above is intended for a sample of least 200 ml. However, a smaller sample size (100 ml) can be distilled by using a smaller distillation flask, provided a splashhead or some other device to prevent entrainment is used.U.K.
5.Storage of test samplesU.K.
Samples are stored at room temperature prior to analysis.
6.ProcedureU.K.
Preliminary remark:
Distillation may also be by the procedure published by IUPAC (1968).
6.1.Distillation apparatus verification.U.K.
The apparatus used must be capable of the following:
The distillation of 200 ml of a water-alcohol solution with known concentration close to 50 % vol must not cause a loss of alcohol of more than 0,1 % vol.
6.2.Spirit drinks with alcoholic strength below 50 % vol.U.K.
Measure out 200 ml of the spirit into a volumetric flask.
Record the temperature of this liquid, or maintain at standard temperature (20 °C).
Pour the sample into the round-bottomed flask of the distillation apparatus and rinse the volumetric flask with three aliquots each of approximately 20 ml of distilled water. Add each rinse water aliquot to the contents of the distillation flask.
Note:U.K.
This 60-ml dilution is sufficient for spirits containing less than 250 g of dry extract per litre. Otherwise, to prevent pyrolysis, the volume of rinse water must be at least 70 ml if the dry extract concentration is 300 g/l, 85 ml for 400 g/l dry extract, and 100 ml for 500 g/l dry extract (some fruit liqueurs or crèmes). Adjust these volumes proportionally for different sample volumes.U.K.
Add a few anti-bumping granules (3.1) (and antifoam for crème liqueurs).
Pour 20 ml of distilled water into the original 200 ml volumetric flask that will be used to hold the distillate. This flask must then be placed in a cold water bath (4.1) (10 to 15 °C for aniseed-flavoured spirit drinks).
Distil, avoiding entrainment and charring, occasionally agitating the contents of the flask, until the level of distillate is a few millimetres below the calibration mark of the volumetric flask.
When the temperature of this distillate has been brought down to within 0,5 °C of the liquid's initial temperature, make up to the mark with distilled water and mix thoroughly.
This distillate is used for the determination of alcoholic strength by volume (Appendix II)
6.3.Spirit drinks with alcoholic strength above 50 % vol.U.K.
Measure out 100 ml of the spirit drink into a 100-ml volumetric flask and pour into the round bottomed flask of the distillation apparatus.
Rinse the volumetric flask several times with distilled water and add the washings to the contents of the round-bottomed distillation flask. Use enough water to bring the flask's contents up to approximately 230 ml.
Pour 20 ml of distilled water into a 200-ml volumetric flask that will be used to hold the distillate. This flask must then be placed in a cold water bath (4.1) (10 to 15 °C for aniseed-flavoured spirits).
Distil, agitating the contents occasionally, until the level of distillate is a few millimetres below the calibration mark of the 200-ml volumetric flask.
When the temperature of this distillate has been brought down to within 0,5 °C of the liquid's initial temperature, make up to the mark with distilled water and mix thoroughly.
This distillate is used for the determination of alcoholic strength by volume (Appendix II)
Note:U.K.
The alcoholic strength by volume of the spirit drink is twice the alcoholic strength of the distillate.U.K.
APPENDIX II: MEASUREMENT OF DENSITY OF DISTILLATEU.K.
METHOD A:DETERMINATION OF REAL ALCOHOLIC STRENGTH BY VOLUME OF SPIRIT DRINKS — MEASUREMENT BY PYCNOMETRYU.K.
A.1.PrincipleU.K.
The alcoholic strength by volume is obtained from the density of the distillate measured by pycnometry.
A.2.Reagents and materialsU.K.
During the analysis, unless otherwise is stated, use only reagents of recognised analytical grade and water of at least grade 3 as defined in ISO 3696:1987.
A.2.1.Sodium chloride solution (2 % w/v)U.K.
To prepare 1 litre, weigh out 20 g of sodium chloride and dissolve to 1 litre using water.
A.3.Apparatus and EquipmentU.K.
Usual laboratory apparatus and in particular the following:
Analytical balance capable of reading 0,1 mg.
Thermometer, with ground glass joint, calibrated in tenths of a degree from 10 to 30 °C. This thermometer must be certified or checked against a certified thermometer.
Pyrex-glass pycnometer of approximately 100 ml capacity fitted with a removable ground-glass thermometer (A.3.2). The pycnometer has a side tube 25 mm in length and 1 mm (maximum) in internal diameter ending in a conical ground joint. Other pycnometers as described in ISO 3507, e.g. 50 ml may be used if appropriate.
A tare bottle of the same external volume (to within 1 ml) as the pycnometer and with a mass equal to the mass of the pycnometer filled with a liquid of density 1,01 (sodium chloride solution A.2.1).
Thermally insulated jacket that fits the body of the pycnometer exactly.
Note 1:U.K.
The method for determining the densities in vacuo of spirits calls for the use of a twin-pan balance, a pycnometer and a tare bottle of the same outside external volume to cancel out the effect of air buoyancy at any given moment. This simple technique may be applied using a single-pan balance provided that the tare bottle is weighed again to monitor changes in air buoyancy over time.U.K.
A.4.ProcedureU.K.
Preliminary remarks:
The following procedure is described for the use of 100-ml pycnometer for determination of the alcoholic strength; this gives the best accuracy. However, it is also possible to use a smaller pycnometer, for example 50 ml.
A.4.1.Calibration of pycnometerU.K.
The pycnometer is calibrated by determining the following parameters:
tare of the empty pycnometer,
volume of the pycnometer at 20 °C,
mass of the water-filled pycnometer at 20 °C.
A.4.1.1.Calibration using a single-pan balance:U.K.
Determine:
the mass of the clean, dry pycnometer (P),
the mass of the water-filled pycnometer at t °C (P1),
the mass of the tare bottle (T0).
A.4.1.1.1.Weigh the clean, dry pycnometer (P).U.K.
A.4.1.1.2.Fill the pycnometer carefully with distilled water at ambient temperature and fit the thermometer.U.K.
Carefully wipe the pycnometer dry and place it in the thermally-insulated jacket. Agitate by inverting the container until the thermometer's temperature reading is constant.
Set the pycnometer flush with the upper rim of the side tube. Read the temperature t °C carefully and if necessary correct for any inaccuracies in the temperature scale.
Weigh the water-filled pycnometer (P1).
A.4.1.1.3.Weigh the tare bottle (T0).U.K.
A.4.1.1.4.CalculationU.K.
Tare of the empty pycnometer = P – m
where m is the mass of air in the pycnometer.
m = 0,0012 × (P1 – P)
Note 2:U.K.
0,0012 is the density of dry air at 20 °C at a pressure of 760 mm HgU.K.
Volume of the pycnometer at 20 °C:
where Ft is the factor for temperature t °C taken from Table I of Chapter 1 ‘Density and specific gravity’ of the Annex to Regulation (EEC) No 2676/90 (p. 10).
V20 °C must be known to the nearest 0,001 ml.
Mass of water in the pycnometer at 20 °C:
where 0,998203 is the density of water at 20 °C.
Note 3:U.K.
If necessary, the value 0,99715 of the density in air can be used and the alcoholic strength calculated with reference to the corresponding density in HM Customs and Excise tables in air.U.K.
A.4.1.2.Calibration method using a twin-pan balance:U.K.
Place the tare bottle on the left-hand pan and the clean, dry pycnometer with its collecting stopper on the right-hand pan. Balance them by placing weights on the pycnometer side: p grams.
Fill the pycnometer carefully with distilled water at ambient temperature and fit the thermometer; carefully wipe the pycnometer dry and place it in the thermally insulated jacket; agitate by inverting the container until the thermometer's temperature reading is constant.
Accurately adjust the level to the upper rim of the side tube. Clean the side tube, fit the collecting stopper; read the temperature t °C carefully and if necessary correct for any inaccuracies in the temperature scale.
Weigh the water-filled pycnometer, with p′ the weight in grams making up the equilibrium.
CalculationU.K.
Tare of the empty pycnometer = p + m
where m is the mass of air in the pycnometer.
m = 0,0012 × (p – p′)
Volume of the pycnometer at 20 °C:
where Ft is the factor for temperature t °C taken from Table I of Chapter 1 ‘Density and specific gravity’ of the Annex to Regulation (EEC) No 2676/90 (p. 10).
V20 °C must be known to the nearest 0,001 ml.
Mass of water in the pycnometer at 20 °C:
where 0,998203 is the density of water at 20 °C.
A.4.2.Determination of alcoholic strength of test sampleU.K.
Using a single-pan balance.
Weigh the tare bottle, weight T1.
Weigh the pycnometer with the prepared distillate (see Appendix I), P2 is its weight at t °C.
CalculationU.K.
Mass of empty pycnometer at moment of measuring
= P - m + dT
Mass of the liquid in the pycnometer at t °C
= P2 - (P - m + dT)
Density at t °C in g/ml
Express the density at t °C in kilograms per m3 by multiplying ρt °C by 1 000, the value being known as ρt.
Correct ρt to 20 using the table of densities ρT for water-alcohol mixtures (Table II of Appendix II to the OIV's manual of analysis methods (1994), pp. 17-29).
In the table find the horizontal line corresponding to temperature T in whole degrees immediately below t °C, the smallest density above ρt. Use the table difference found below that density to calculate the density ρt of the spirit at that temperature T in whole degrees.
Using the whole temperature line, calculate the difference between density ρ′ in the table immediately above ρt and the calculated density ρt. Divide that difference by the table difference found to the right of density ρ′. The quotient provides the decimal portion of the alcoholic strength while the integer of the alcoholic strength is found at the top of the column in which density ρ′ is found (Dt, the alcoholic strength).
Note 4:U.K.
Alternatively keep the pycnometer in a water bath maintained at 20 °C (± 0,2 °C) when making up to the mark.U.K.
ResultU.K.
Using the density ρ20 calculate the real alcoholic strength using the alcoholic strength tables identified below:
The table giving the value of the alcoholic strength by volume (% vol) at 20 °C as a function of the density at 20 °C of water-alcohol mixtures is the international table adopted by the International Legal Metrology Organisation in its Recommendation No 22.
A.5.Method performance characteristics (precision)U.K.
A.5.1.Statistical results of the interlaboratory testU.K.
The following data were obtained from an international method performance study carried out to internationally agreed procedures [1] [2].
| Year of interlaboratory test | 1 997 |
| Number of laboratories | 20 |
| Number of samples | 6 |
METHOD B:DETERMINATION OF REAL ALCOHOLIC STRENGTH BY VOLUME OF SPIRIT DRINKS — MEASUREMENT BY ELECTRONIC DENSIMETRY (BASED ON THE RESONANT FREQUENCY OSCILLATION OF A SAMPLE IN AN OSCILLATION CELL)U.K.
B.1.PrincipleU.K.
The liquid's density is determined by electronic measurement of the oscillations of a vibrating U-tube. To perform this measurement, the sample is added to an oscillating system, whose specific oscillation frequency is thus modified by the added mass.
B.2.Reagents and materialsU.K.
During the analysis, unless otherwise is stated, use only reagents of recognised analytical grade and water of at least grade 3 as defined in ISO 3696:1987.
Acetone (CAS 666-52-4) or absolute alcohol
Dry air.
B.3.Apparatus and equipmentU.K.
Usual laboratory apparatus and in particular the following:
Digital display densimeterU.K.
Electronic densimeter for performing such measurements must be capable of expressing density in g/ml to 5 decimal places.
Note 1:U.K.
The densimeter should be placed on a perfectly stable stand that is insulated from all vibrations.U.K.
Temperature regulationU.K.
The densimeter's performance is valid only if the measuring cell is connected to a built-in temperature regulator that can achieve the same temperature stability of ± 0,02 °C or better.
Note 2:U.K.
The precise setting and monitoring of the temperature in the measuring cell are very important, for an error of 0,1 °C can lead to a variation in density of the order of 0,1 kg/m3.U.K.
Sample injection syringes or auto sampler.
B.4.ProcedureU.K.
Calibration of the densimeterU.K.
The apparatus must be calibrated according to the instrument manufacturer's instructions when it is first put into service. It must be recalibrated regularly and checked against a certified reference standard or an internal laboratory reference solution based on a certified reference standard.
Determination of sample densityU.K.
If required prior to measurement clean and dry the cell with acetone or absolute alcohol and dry air. Rinse the cell with the sample.
Inject the sample into the cell (using a syringe or autosampler) so that the cell is completely filled. During the filling operation make sure that all air bubbles are completely eliminated. The sample must be homogeneous and must not contain any solid particles. Any suspended matter should be removed by filtration prior to analysis.
Once the reading has stabilised, record the density ρ20 or the alcoholic strength displayed by the densimeter.
ResultU.K.
When the density ρ20 is used, calculate the real alcoholic strength using the alcoholic strength tables identified below:
The table giving the value of the alcoholic strength by volume (% vol) at 20 °C as a function of the density at 20 °C of water-alcohol mixtures is the international table adopted by the International Legal Metrology Organisation in its Recommendation No 22.
B.5.Method performance characteristics (precision)U.K.
B.5.1.Statistical results of the interlaboratory testU.K.
The following data were obtained from an international method performance study carried out to internationally agreed procedures [1] [2].
| Year of interlaboratory test | 1 997 |
| Number of laboratories | 16 |
| Number of samples | 6 |
METHOD C:DETERMINATION OF REAL ALCOHOLIC STRENGTH BY VOLUME OF SPIRIT DRINKS — MEASUREMENT BY DENSIMETRY USING HYDROSTATIC BALANCEU.K.
C.1.PrincipleU.K.
The alcoholic strength of spirits can be measured by densimetry using a hydrostatic balance based on Archimedes' principle according to which a body immersed in a liquid receives a vertical upward thrust from the liquid equal to the weight of liquid displaced.
C.2.Reagents and materialsU.K.
During the analysis, unless otherwise is stated, use only reagents of recognised analytical grade and water of at least grade 3 as defined in ISO 3696:1987.
C.2.1.Float cleaning solution (sodium hydroxide, 30 % w/v)U.K.
To prepare 100 ml, weigh 30 g of sodium hydroxide and make up to volume using 96 % volume ethanol.
C.3.Apparatus and EquipmentU.K.
Usual laboratory apparatus and in particular the following:
Single-pan hydrostatic balance with a sensitivity of 1 mg.
Float with a volume of at least 20 ml, specially adapted to the balance, suspended with a thread of diameter not exceeding 0,1 mm.
Measuring cylinder bearing a level mark. The float must be capable of being contained completely within the volume of the cylinder located below the mark; the surface of the liquid may only be penetrated by the supporting thread. The measuring cylinder must have an internal diameter at least 6 mm larger than that of the float.
Thermometer (or temperature-measuring probe) graduated in degrees and tenths of a degree from 10 to 40 °C, calibrated to 0,05 °C.
Weights, calibrated by a recognised certifying body.
Note 1:U.K.
Use of a twin-pan balance is also possible; the principle is described in Chapter 1 ‘Density and specific gravity’ of the Annex to Regulation (EEC) No 2676/90 (p. 7).U.K.
C.4.ProcedureU.K.
The float and measuring cylinder must be cleaned between each measurement with distilled water, dried with soft laboratory paper which does not shed fibres and rinsed with the solution whose density is to be determined. Measurements must be made as soon as the apparatus has reached stability so as to restrict alcohol loss by evaporation.
Calibration of the balanceU.K.
Although balances usually have an internal calibration system, the hydrostatic balance must be capable of calibration with weights checked by an official certifying body.
Calibration of the floatU.K.
Fill the measuring cylinder to the mark with double-distilled water (or water of equivalent purity, e.g. microfiltered water with a conductivity of 18,2 MΩ/cm) at a temperature between 15 and 25 °C but preferably at 20 °C.
Immerse the float and the thermometer, stir, read off the density of the liquid from the apparatus and, if necessary, correct the reading so that it is equal to that of the water at measurement temperature.
Control using a water-alcohol solutionU.K.
Fill the measuring cylinder to the mark with a water-alcohol mixture of known strength at a temperature between 15 and 25 °C but preferably at 20 °C.
Immerse the float and the thermometer, stir, read off the density of the liquid (or the alcoholic strength if this is possible) from the apparatus. The alcoholic strength thus established should be equal to the previously determined alcoholic strength.
Note 2:U.K.
This solution of known alcoholic strength can also be used to calibrate the float instead of double-distilled water.U.K.
Measurement of the density of a distillate (or of its alcoholic strength if the apparatus allows)U.K.
Pour the test sample into the measuring cylinder up to the graduation mark.
Immerse the float and the thermometer, stir, read off the density of the liquid (or the alcoholic strength if this is possible) from the apparatus. Note the temperature if the density is measured at t °C (ρt).
Correct ρt to 20 using the table of densities ρT for water-alcohol mixtures (Table II of Annex II to the OIV's Manual of analysis methods (1994), pp. 17-29).
Cleaning of float and measuring cylinderU.K.
Immerse the float in the float cleaning solution in the measuring cylinder.
Allow to soak for one hour spinning the float periodically.
Rinse with copious amounts of tap water followed by distilled water.
Dry with soft laboratory paper which does not shed fibres.
Carry out this procedure when the float is first used and then regularly as required.
ResultU.K.
Using the density ρ20 calculate the real alcoholic strength using the alcoholic strength tables identified below.
The table giving the value of the alcoholic strength by volume (% vol) at 20 °C as a function of the density at 20 °C of water-alcohol mixtures is the international table adopted by the International Legal Metrology Organisation in its Recommendation No 22.
C.5.Method performance characteristics (precision)U.K.
C.5.1.Statistical results of the interlaboratory testU.K.
The following data were obtained from an international method performance study carried out to internationally agreed procedures [1] [2].
| Year of interlaboratory test | 1 997 |
| Number of laboratories | 12 |
| Number of samples | 6 |
1-litre round-bottomed flask with standardised spherical ground-glass joint.
20-cm Vigreux rectifying column.
10-cm straight-rimmed West condenser.
40-cm cooling coil.