The sensorial evaluation of grape berries is a supplementary means of determining the degree of ripeness or the suitability of grapes for a specific wine style.
It does not replace other analyses of ripeness such as sugar, acid, colour or vineyard evaluation, but should be considered a complementary aid. Using fingers, eyes, ears and mouth, it entails the evaluation of fresh grape berries with regard to the berry stem, skin, flesh and grapeseeds. Berry evaluation means that the skin, flesh and grapeseed are evaluated independently.
Grape characteristics that may influence the style of the wine are the absence of negative properties (such as mustiness due to mouldy growth, a vinegary taste ascribed to acetic acid bacteria, sunburn or ash and dust contamination), the physical appearance, analytical properties, flavours and phenolic composition of the grapes.
The absence of negative properties is important in view of the fact that the above-mentioned factors may have a negative influence on wine stability, flavour composition, oxidative stability and colour stability.
The physical characteristics of the grapes may be evaluated by looking at the berry’s firmness, the ease with which the berry may be pulled from the brush, the segregation of flesh, skin and seed, uniformity of the berry flesh, skin colour and skin integration and colour of the grapeseed. Berries soften during ripening and the skin does not adhere as much to the flesh of the berry. These physical changes assist the release of colour and flavour during red wine fermentation.
Not only do the sugar and fixed acid content of grapes and the ratio thereof play an important individual role, they are also conclusive in the balance of the eventual wine. The sugar content will determine the eventual alcohol content, but seeing that accurate sensorial measurement of the former is not possible, sugar analyses of the grapes are essential. The sensorial evaluation of berries cannot determine the acid content either, although it does give an indication of the perception or sensation of acid. Seeing that pH is a direct indication of acid perception, it plays an important role, together with sugar and total acid content of grapes. If the grapes have a good pH, good colour is ensured, as well as control over the microbiological stability of wines.
The aroma of wine may be divided into herbaceous, floral, fruity and cultivar aromas.
The herbaceous aromas of grape berries derive from two sources. The straw or grassy aromas are especially noticeable when chewing the grape skins while the pepper, green pepper or asparagus aromas are metoxypyrazines occurring in the skin and grapeseed in particular. These usually diminish during ripening. They are not influenced by alcoholic fermentation and if detected in the grapes, they will also occur in the wine. This is particularly noticeable in Cabernet Sauvignon, Sauvignon blanc, Merlot and Semillon during the harvest.
Floral aromas occur mainly in the berry skin and in the flesh close to the skin. Examples are linalol which is also evident in roses, as well as the violet aroma occurring in certain red and muscat grapes.
The fruity aromas form the backbone of wine descriptions and play an important role in the consumer’s decision to buy wine. There are four main groups of fruity aromas, making it easy to identify cultivars. Firstly the citrus aromas, secondly those reminiscent of stewed apples or ripe watermelon or peach, thirdly the banana and berry characters and fourthly the grapefruit and pineapple aromas.
Each cultivar has a specific aroma potential which is largely determined by the stage of pressing. On the whole herbaceous aromas dominate in grapes that are picked early, to be followed by floral citrus aromas and fruity aromas in the later stages of pressing the grapes. The aromas of different cultivars will therefore change depending on the stage at which the grapes are pressed. The following is an indication of how the aroma will change depending on the increasing ripeness of the grapes:
Riesling: Floral, perfumey, apple, pear, citrus, lime, granadilla, tropical fruit. Sauvignon blanc: Asparagus, green pepper, herb, grassy, gooseberry, tropical fruit. Semillon: Herb, straw, gooseberry, apple, quince, lemon, lime, granadilla, tropical fruit. Chardonnay: Cucumber, grapefruit, gooseberry, apple, lime, watermelon, peach, fruit salad, fig, tropical fruit. Pinot noir: Cherry, strawberry, violet, raspberry, plum, stewed prune. Grenache: Floral, boiled sweets, spicy, raspberry, pepper, plum, stewed prune, prune, liquorice. Merlot: Herb, leaf, fruity, violet, cherry, raspberry, plum, fruit cake, blackberry. Cabernet Sauvignon: Herb, capsicum, tomato bush, leaf, mint, dusty, black olive, blackberry. Shiraz: Herb, spice, raspberry, plum, peppery, blackberry, mulberry, liquorice, black olive, jam.
Colour is important in both white and red wines. The gradual change from a green to a golden tinge in white wines may for example indicate the degree of ripeness of the grapes. The concentration of red colour in red wines is also influenced by factors such as the colourants that had been formed before the harvest, the skin to berry ratio, skin ripeness, pH and phenols that may stabilise the colour.
The influence of phenolic concentration and the quality of the grapes on the quality of the wine is very important. During red wine fermentation different concentrations of phenols may be extracted and skin contact and pressing processes may also result in an increase in the phenol quality of white wines. The extractability of phenols from the skin increases during ripening while it decreases in the grapeseeds. If skins or grapeseeds are chewed, a reaction occurs between the saliva and the phenols. If a large quantity of phenols reacts with the saliva, the viscosity of the saliva will decrease. This will obviously increase the friction of the saliva in the mouth.
The sensorial evaluation of berries is not only a theoretical exercise, however, and evaluation panels must be properly trained. Methods are described to implement such training. Examples of tasting charts to be used, are also illustrated.
Winter, E, Whiting, J & Rousseau, J, 2004. Winetitles, Adelaide.
The above book may be ordered from www.winetitles.com.au.