AOAC Official Method
Alcohol by Volume
in Distilled Liquors
Densitometric Method
First Action 1982
Final Action 1985
A. Principle
Meter determines specific gravity at 20° C by measuring change in
frequency of oscillating U-tube filled with test portion compared
with frequencies of oscillation when filled with 2 standards. Specific
gravity is converted to % alcohol by volume at ° C.
B. Apparatus and Reagents
(a) Density meter.—Mettler/Parr DMA 55D or equivalent.
Autosampler optional.
(b) Water bath.—Constant temperature, controlled at
– ° C.
(c) Syringe.—10 mL, with Luer fitting, No. 15 needle.
(d) Water.—Double-distilled or treated by ion exchange resin and
filtered, freshly boiled (ion exchange cartridge, research model, sold
by Illinois Water Treatment Co., 4669 Shepherd Trail, Rockford, IL
61105-0506, USA; Gelman Capsule Filter, Cat. No. 12106, m m,
Gelman Sciences, Inc.).
(e) Thermometer.— to ° C, ° C scale divisions (No.
116-C, H&B Instrument Co., American and Bristol St, Philadelphia,
PA 19140, USA).
C. Standardization of Density Meter
Rinse U-tube with stream of acetone, and completely dry with air
stream. Set switches on density meter in the following positions:
power-on, display-T, sampling rate-either 2 or 3. With clean, dry
U-tube at 20 – ° C, note and record T for air.
Turn on light and open shutter to view U-tube. Fill U-tube with freshly
boiled double-distilled (or ion exchange-treated) H2O by dipping plastic
tube connected to inlet (lower) end of U-tube into H2O standard and
slowly pulling plunger on syringe, equipped with No. 15 needle, con-
nected by plastic tubing to outlet (upper) of U-tube. View U-tube to en-
sure that it is full of H2O and contains no bubbles. Leave end of filler tube
submerged in H2O standard and syringe connected while taking reading.
Turn off viewing light and close shutter. T value of H2O on digital display
will continue to change until test portion temperature reaches equilibrium
with constant temperature bath (ca 2–3 min). Record T for H2O.
Calculate apparatus constants A and B as follows:
A = [T 2 (H2O) - T 2 (air)]
B = T 2 (air)
Enter calculated values of constants A and B into apparatus mem-
ory by rotating appropriate dials. Reset display switch to r (specific
gravity), and check reading for specific gravity of H2O. Then drain
U-tube, dry, and check specific gravity of air. Numerical displays
should be apparent specific gravity for H2O, and
apparent specific gravity for air. If display values differ >1 in fifth
decimal place from correct specific gravity values, recheck tempera-
ture of H2O bath and T for air and H2O.
D. Specific Gravity Measurement of Test Portions
Turn on light and open shutter to view U-tube. Slowly fill U-tube
with test portion by same method used to fill with H2O standard,
being careful not to introduce bubbles. Turn off viewing light and
close shutter. Specific gravity of test portion on digital display will
continue to change until temperature reaches equilibrium with con-
stant temperature bath (ca 2–3 min). Record specific gravity of test
portion, and draw another test portion into U-tube. Replicate read-
ings should vary £ – specific gravity unit. Refer to Ta-
ble (see Appendix C) to convert specific gravity at 20 ° C to
percent alcohol at ° C.
E. Changing Test Portions
Turn on light and open shutter to view U-tube. Lift inlet end of
plastic tubing from below surface of old test portion and slowly
pull syringe plunger to empty tubing and U-tube. Disconnect sy-
ringe from plastic tubing and discard syringe contents. Reconnect sy-
ringe, submerge tip of tubing below surface of new test portion, and
slowly draw 8–10 mL test portion through U-tube into syringe to elimi-
nate air bubbles and to rinse system with new test portion. Turn off view-
ing light, close shutter, and take first reading of new test portion after
temperature equilibrium.
After each 10 test portions, or when erratic digital displays are
noted, rinse U-tube with acetone and dry with air stream. Let empty
U-tube stabilize at 20 – ° C.
Reference: JAOAC 65, 218(1982).
CAS-64-17-5 (alcohol)
