Project Number
WW 08-32

Project title
Improvement of the stability of port wine colour

Project leader
Van Jaarsveld, F P

Team members
Augustyn, O P H
Burger, I
Ellis, L P
October, F M

Project description
The South African Port Producers Association (SAPPA) requested an investigation into the improvement of the stability of port wine colour. Colour is one of the principal parameters of the quality of red wines, since it is the first characteristic to be perceived in the glass. The colour also gives an indication of possible defects, the body, the age and the evolution of the wine during storage. Colour therefore has an important influence on the overall acceptability of the product to the consumer. During aging, the wine colour undergoes changes, mainly due to progressive structural changes of anthocyanins.

The first aim of this project is to compile a database containing sensory and colour data of commercially available Cape Vintage Ports and Cape Vintage Reserve Ports, Cape Ruby and Cape Tawny Ports, as well as a selection of Portuguese Ports.

The second aim is to study the effect of practices in the cellar and in the vineyard on colour and colour stability, by subjecting samples to accelerated conditions. The initial investigation in the cellar will involve the following:

Wine spirit used for fortification has different aldehyde levels. These aldehydes may play a role in colour stability. Aldehydes also have an effect on the sensory quality of the port wine which will be investigated simultaneously. The effect of the aldehyde content of different wine spirits on total port wine quality will therefore be investigated.

Thermovinification, where juice is heated with the grape skins before pressing, to improve colour extraction, will be investigated. This extraction technique will enable us to obtain must and port wine samples which may be more susceptible to colour instability problems.

The samples from both studies will also be subjected to a sensory evaluation. As far as conditions in the vineyard are concerned, information on cultivar, terroir, etc. (where available), gathered from the producers, will be correlated with information in the database. These results may lead to further studies in the vineyard.

– Record end –