Factors affecting port wine colour stability

Abstract

Port is a wine style that comes from Portugal. It is a sweet fortified dessert wine that is made in red and white styles. The taste is a balanced and complex combination of berry fruit, acidity, sweetness, alcohol and tannins. The taste should be sweet, smooth, complex, with some spiciness and a dry finish, but not astringent (Anon., 2009). There are a variety of port types in terms of flavour intensity, aroma and sweetness levels. Young immature ports can be fruity, simple, coarse, spicy and astringent. The sweetness results from the natural grape sugar in the wine, while wine spirits is added to fortify and ensure microbiological stability during aging (Anon., 2009). In this study the work was done on the ruby port style wine, ruby port wine is well known for its characteristic of being bright red in colour and therefore also very difficult to preserve in terms of colour stability in general. Colour is one of the principle parameters of the quality of not only port wine but also red wine in general, since it is the first characteristic to be perceived by the consumer in the glass. The colour of port wine also gives an indication of possible defects, the body, 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 changes, mainly due to progressive structural changes of anthocyanins. These changes are often perceived as undesirable by port consumers. As a result, the Cape Port Producers Association (CAPPA) requested this type of research to be done on port wine to improve the port wine making process in order to also give port wine a more stable colour. Therefore the objective of this study was to manipulate some of the parameters in port wine making, such as type of spirit used to fortify, storage temperature and also storage time in order to improve optimum stability of port wine colour. From the first part of the study it was evident that the type of fortifying spirits, storage time and temperature had a significant effect on the colour of the port wine samples. The 96.5% (v.v-1) fortifying spirits, shorter storage time and storage temperature below 25oC resulted in a more stable ruby port colour as well as the lowest change over time. As the study progressed the design variables differed in terms of two types of cultivars used the spirits used to fortify the port wine samples with, addition of a pectolytic enzyme to some of the port wine samples, as well as storage time of 12 months and only two storage temperatures. It could be concluded that at the end of this part of the study, that port wine colour stability was affected by the interaction of the design variables in each treatment and less so by individual design variables in the study. It could also be concluded in this study that higher levels of acetaldehyde present in the spirits used to fortify port wine, did have a significant impact on ruby port wine and colour stability. The application of pectolytic enzyme preparation does not necessarily have a significant effect on its own but depends on the type of cultivar used. Storage time and temperature should also be kept to a minimum to ensure the desirable bright red colour of a ruby port wine.