Measurement of red grape colour

This document gives a brief summary of the procedures and equipment requirements for some commonly used techniques for determination of the red grape colour. There are several techniques of varying degree of difficulty and capital cost that are used to measure red grape colour.

Spectrophotometric

Description: The laboratory method for determination of total anthocyanins (Iland et al. 1996, 2000) involves homogenisation of a known defined amount of grape berries, followed by extraction of colour into an acidified ethanol solution. The extract is then measured for absorbance at 520 nm using a UV/visible spectrophotometer which is then converted to an equivalent concentration of malvidin-3-glucoside using the method of extinction coefficient.
Equipment: Homogeniser, UV/visible spectrophotometer, autopipettes, centrifuge, balance
Reagents: Acidified ethanol, standard
Calibration: UV/visible spectrophotometer as per manufacturer’s instructions
Services: Wash up area, electricity
Space required: Bench space depending on UV/visible spectrophotometer footprint

Near infrared spectroscopy (NIR)

Description: Homogenates of grape berries are scanned directly using a scanning NIR spectrophotometer (relatively high capital cost) usually in reflectance mode. Near infrared spectroscopy is a correlative technique that requires the use of a robust calibration for the types of samples being analysed (Dambergs et al. 2003). The calibration is usually developed against the spectrophotometric laboratory method described above as reference and will therefore include the accuracy errors associated with that method. The method can be very precise and extremely fast.
Equipment: NIR spectrophotometer
Calibration: As recommended by manufacturers, check against reference methods
Services: Wash up area, electricity
Space required: Bench space depending on instrument footprint

References and further reading

  • Dambergs, R.G.; Cozzolino, D.; Esler, M.B.; Cynkar, W.U.; Kambouris, A.; Francis, I.L.; Hoj, P.B.; Gishen, M. (2003) The use of near infrared spectroscopy for grape quality measurement. Aust. N.Z. Grapegrower Winemaker No. 473a: 69-74, 76.
  • Iland, P.G.; Cynkar, W.U.; Francis, I.L.; Williams, P.J.; Coombe, B.G. (1996) Optimisation of methods for the determination of total and red-free glycosyl glucose in black grape berries of Vitis Vinifera. Aust. J. Grape Wine Res. 2(3): 171-178.
  • 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.
  • Zoecklein, B.W.; Fugelsang, K.C.; Gump, B.H.; Nury, F.S. (1995) Wine analysis and production. New York Chapman & Hall.