The measurement of colour in Pinot noir wine

Abstract

The nature of colour in wines has been extensively studied over the years, with Pinot noir wines often being characterised by their light colour. The association of colour and perceived quality has also been widely researched for food and beverages, indicating that colour has a strong influence on product preference by the consumer.

This study was undertaken in order to assess the most accurate method for determining Pinot noir wine colour in terms of what the human eye perceives. Colour analyses were undertaken with the use of CIELAB (HunterLab), spectrophotometric and sensory evaluation parameters and the extent to which the colour measurements could be compared and correlated was evaluated. There are clear advantages in the objective quantification of colour measurement, because when a colour is defined numerically it can then be statistically compared and tolerances or levels established for quality control.

Pinot noir wines from the 1998 and 2000 vintages were selected as representatives of a high phenolic (heavy) and low phenolic (light) style wine. The wines demonstrated notable differences in colour and were dark red-purple and a light red, salmon pink colour respectively.

In order to provide a range of colours from which measurements could be taken, the two wine styles were subjected to a short-term accelerated ageing test. The accelerated ageing process consisted of the wines being held for a 3 week period at 45°C, followed by 1 week at room temperature (20°C). These wines were labelled 'aged,' and the untreated wines held at cellar temperatures (13°C) for the 28 day treatment period were labelled 'control.' Each treatment was sampled and analysed at 7 day intervals.

The spectrophotometric and CIELAB parameters for the light style wine after accelerated ageing indicated that the wine became darker and increased in both redness and yellowness simultaneously. Similarly, the wine was shown to increase in sensory colour density and yellow/browness, but not redness. Therefore, the HunterLab and spectrophotometer instruments appeared to yield more precise measurements in the red area of the colour spectrum, which was not comparable to the colour seen by the human eye. The CIELAB (HunterLab) parameters indicated an increase in redness and yellowness of the heavy style wine after accelerated ageing, whereas the spectrophotometric measurements depicted an increase in yellowness but not redness. With reference to the sensory evaluation results it can be concluded that the spectrophotometer provided a superior measure of browness in the age-treated heavy style wine in terms of what the eye perceives. However, the CIELAB assessment of redness (a*) demonstrated an increased level of discrimination with regard to colour assessment.

CIELAB (HunterLab) and spectrophotometric measurements taken for the light style control wine did not depict comparable instrumental colour trends. The majority of colour trends outlined by the sensory evaluation were also not in agreement with these instrumental measures. All parameters attributing to yellowness or browness (b*, E420, yellow/browness) proved to be unsuitable for the evaluation of the untreated light style Pinot noir wine colour. However, the spectral measure of redness (E520) and the a* coordinate (redness) were found to be closely correlated to an increase in sensory colour density.

No overall changes in colour were recorded by any of the measurements undertaken on the heavy style control wine.