Measurement of alcohol content of wine

This document gives a brief summary of the procedures and equipment requirements for some commonly used techniques for determination of the alcohol content of wines. There are several techniques of varying degree of difficulty and analytical accuracy that are used to measure the alcohol content of wine.

Ebulliometry

Description: This technique is based on the depression of boiling point of water with increasing ethanol content. There are several interferences that will detrimentally affect the accuracy of measurements made by this technique, one of the most important being interference by sugar (Zoecklein et al. 1995). The accuracy of this technique is generally about 0.5% alcohol, and is therefore not recommended for use when making determinations of alcohol content used for label declarations.

Equipment: Ebulliometer including thermometer
Services: Wash up area
Space required: Minimal bench space

Distillation/hydrometry

Description: Distillation of a wine sample separates the volatile from the non-volatile components. The alcohol content of the resulting distillate can then be readily measured by hydrometry using appropriately scaled alcohol hydrometers. The measurement is subject to temperature effects and therefore the temperature must be measured and the observed reading corrected using published tables.

Equipment: Distillation apparatus, alcohol hydrometer, measuring cylinder, thermometer, retort stands and clamps
Calibration: Pre-calibrated, check with made-up standard solutions of ethanol in water
Services: Flame burner, condenser water, wash up area
Space required: Bench space

Distillation/densitometry

Description: Distillation of a wine sample separates the volatile from the non-volatile components. The alcohol content of the resulting distillate can then be readily measured using a density meter (or alternatively, by using a pycnometer). Density meters can measure the density of a test liquid with great precision, although the temperature of the sample must be well controlled. The density reading can then be converted to alcohol content by reference to published tables, although many density meters have in-built conversion scales.

Equipment: Distillation apparatus, retort stands and clamps, density meter (or pycnometer), analytical balance to four decimal points (if using a pycnometer)
Calibration: Pre-calibrated, check with made-up standard solutions of ethanol in water
Services: Flame burner, condenser water, wash up area
Space required: Bench space depending on instrument footprint

Near infrared spectroscopy (NIR) and mid infrared (MIR) spectroscopy

Description: Samples of wine are scanned directly in the NIR/MIR spectrophotometer, usually in a transflectance cell that is temperature controlled. Near infrared spectroscopy is a correlative technique that requires the use of a robust calibration for the types of samples being analysed. The calibration is usually developed against one of the other reference laboratory methods  and will therefore include the accuracy errors associated with that method. The method can be very precise and extremely fast. Several different NIR/MIR instruments can be purchased with calibrations provided and require only minimal user calibration adjustment.

Equipment: NIR/MIR spectrophotometer
Calibration: Provided by manufacturers, check against reference methods
Services: Wash up area, electricity
Space required: Bench space depending on instrument footprint

Gas chromatography (GC)

Description: Gas chromatography (GC) is a technique that offers several advantages for the analysis of alcohol in wine, including potential for automation, high precision, and it is relatively fast. However, there is a fairly high capital cost and skilled personnel are required to operate and maintain the instrument. Generally, GC is only used for analysis of alcohol where there are other applications of GC being used by the winery on a routine basis.

Equipment: Gas chromatograph
Calibration: Use made-up standard solutions of ethanol in water, internal standard solutions
Services: Electricity, gas bottles
Space required: Significant bench area, gas bottle storage area

References and further reading

  • Amerine, M.A., Ough, C.S. 1980. Methods for analysis of musts and wines. New York Wiley-Interscience.
  • Iland, P., Ewart, A., Sitters, J., Markides, A., Bruer, N. 2000. Techniques for chemical analysis and quality monitoring during winemaking. Campbelltown, SA Patrick Iland Wine Promotions.
  • Rankine, B.C. 1998. Making good wine: a manual of winemaking practice for Australia and New Zealand. South Melbourne, Sun Books (Macmillan Australia).
  • Zoecklein, B.W., Fugelsang, K.C., Gump, B.H., Nury, F.S. 1995. Wine analysis and production. New York Chapman & Hall.