The Latest News & Information from Colour Technologies Australasia and The Novasys Group

FOOD & BEVERAGE INDUSTRY EDITION

*** SPECIAL WINE INDUSTRY ISSUE ***

Volume F4 Issue 4 10 May 2005

Colorimetry by NIR - Who's Confused?

The April 2005 issue of "The Australian and New Zealand Grapegrower and Winemaker" contains an article from the CRC for Viticulture entitled, "Practical and affordable colour measure (sic) for industry".

As long time workers in the field of colour measurement, we were naturally attracted to the article, but we were amazed to read in the very first paragraph, "The rapid measurement of red grape colour and other quality measurements with Near Infrared Spectroscopy throughout the wine industry...." and went on to discuss how wineries could measure colour (total anthocyanins) with a portable NIR instrument that could also measure pH and total solids in red wine grapes.

We have no arguments with NIR as an analytical technique that is probably a valuable tool for measurement of the concentration of anthocyanins and lots of other stuff in red wine grapes, but how this relates to colour leaves us mystified and wondering whether it is us or the CRC that is confused about colour.

In the field of colorimetry and human psychology it is generally accepted that perception of colour is a psychophysical process involving, amongst other things, the modification of light by some means, usually by interaction with a physical object, that is detected by sensors in the eye and interpreted in the brain as "colour". "Light" includes the wavelengths of electromagnetic radiation in the visible range of 400nm to 700nm..

The Near Infra Red Region extends from above 700nm up to around 1200nm and these wavelengths cannot neither be detected by the human eye nor interpreted as colour by humans. NIR instruments detect the interaction of electromagnetic radiation above 700nm with physical objects and these results allow quantification of characteristics of the object, BUT THIS CANNOT BY ANY STRETCH OF THE IMAGINATION BE INTERPRETED AS COLOUR AS WE HUMANS KNOW IT.

The wine industry has some peculiar practices when it attempts to objectively quantify the colour of wines and grapes. "Colour density" is a term that has meaning only within the wine industry. The measurement of red wines at around 520nm (the wavelength of maximum absorbance of anthocyanins in the visible spectrum) is also referred to as "colour measurement". As a means of determining concentration of a colorant, this method has been well known and used in the textile dyeing industry ever since appropriate instrumentation became available decades ago.

The food and beverage industry in general uses colorimetry is a way that brooks no confusion. Objective measurements are made across the visible spectrum in such a way that instrumental measurements can be compared and correlated with visual observations made under standardised conditions. Raw material suppliers, processors and consumers are all talking the same language. Not so with the wine industry where some are visually assessing wine and grape colour, red and white, and others are using analytical techniques and confusing the situation by referring to these as "colour measurement".

We have attempted to communicate our opinions to those in the wine industry who continue to use the term, "colour measurement" in what we believe is an inappropriate way, but they don't want to talk with us!

This is a pity, because colour measurement, "as we know it",  has proven to be a valuable tool for the food and beverage industry and there is no reason why the wine industry should not enjoy similar benefits. Colour measurement instrumentation exists already and is affordable. We don't doubt that inexpensive, portable NIR instrumentation would also benefit the wine maker, but please don't confuse what it does with colour measurement.

One more thing for the person who wrote the CRC article. Instruments measure... machines do work! There is even confusion on this definition within the article.

YOUR comments welcomed - especially if you are working in the wine industry!