Grapes - Crop Post-Harvest: Science and Technology - page 193

1998; Salzman et al . 1998). The timing of the accumulation
of grape osmotin correlates with the inability of the fungal
pathogen powdery mildew ( Uncinula necator ) to initiate
new infections of the berry (Tattersall et al . 1997).
Loulalakis (1997) showed that an osmotin-like gene was
expressed in grape cell cultures exposed to ethylene.

(Saulnier & Brillouet 1988). The expression patterns of
cell wall modifying enzymes during berry development
have been described by Nunan et al . (2001).

POST-HARVEST TECHNOLOGY FOR WINE
AND JUICE GRAPES

Soluble proteins
Proteins in the fruit pulp contribute to clouding of juice and
wine. Recently some authors have described the proteome
of berry skin (Deytieux et al . 2007). The major soluble
proteins appear to be the pathogenesis-related chitinases as
described previously (Pocock et al . 2000). Polyphenol
oxidase (PPO) activity in grapes has been well character-
ised (Okuda et al . 1999; Yokotsuka et al . 1988). The role of
PPO in berry and juice browning is discussed further in
sections on wine and juice grapes and on table grapes
respectively. There is evidence of only one PPO gene in
grape with high levels of expression in young developing
berries, leaves and roots, but little expression in mature
tissues (Dry & Robinson 1994). The compartmentation of
a number of key enzymes in grape berries during develop-
ment is described by Famiani et al . (2000).

Introduction
Wine grapes have not been the subject of much post-harvest
research so far. This may change in the future with trends
towards longer transport times of grapes to wineries, more
mechanically harvested grapes that are more exposed to
post-harvest deterioration and the increasing need to
preserve very delicate fruit flavours. The production of wine
is a complex process which transforms the grape berries into
an alcoholic beverage. Recent topics published on the
science of wine making include Jackson (2000) for North
America, Rankine (1997) for Australia and New Zealand
and Ribéreau-Gayon et al . (1998) and Flanzy (1998) for
France. A quite comprehensive and practical book about
most laboratory analyses has been published by Australian
academics (Iland et al . 2000). A book listing the OIV official
methods for must and wine analyses is also available
(Anonymous 1999).
Fewer than 30 cultivars provide the world's classic
quality wines, all from V. vinifera . Hundreds more are used
to a limited extent. Some important cultivars are: red: pinot
noir, merlot, cabernet sauvignon, shiraz, grenache and
tempranillo; and white: chardonnay, riesling, sauvignon
blanc, chenin blanc, muller thurgau, chasselas, Semillon
and palomino (Galet 2002). There might be interesting aro-
mas to be gained from the use of some other Vitis species.

Cell wall changes
Grape cell walls are composed of about 90% polysaccha-
ride and less than 10% protein. The two main types of
polysaccharides, cellulose and polygalacturonans show
considerable varietal differences in their relative abundance
(Nunan et al . 1997). The firmness of table grapes is an
important quality attribute. Grape berries begin to soften at
veraison and the degree of softening at maturity is
determined largely by cultivar. Although most post-harvest
berry softening has been attributed to loss of water (Nelson
1979), the softening associated with ripening is considered
to result from changes in the composition of the cell walls
(Robinson & Davies 2000). During softening, depolymeri-
zation of pectin and xyloglucan molecules and a decrease
in the amount of hemicellulose and cellulose have been
detected (Yakushiji et al . 2001). Large changes in protein
composition also occur (Nunan et al . 1998). There is a
steady decrease in total pectin substances during grape
ripening and a decrease in methyl-esterification of insolu-
ble pectins (Barnavon et al . 2001). Furthermore levels of
calcium, a mineral which stabilises plant cell walls,
decrease during berry ripening (Cabanne & Doneche
2001). Soluble pectic polymers from mesocarp activity in
juices (also named musts) may play a detrimental role in
white wine making by restricting juice extraction
(Robertson et al . 1980) and delaying must clarification

Harvest maturity requirements
The timing of wine grape harvest is very critical. Too early
and the grapes are too acid. Too late and they may lack
acidity or suffer reduced yields from bird damage or rots.
The berries must contain the correct balance of flavour and
aromatic compounds. The typical maturation levels of sug-
ars should lie between 16% and 24% and acid between
0.6% and 1%. The yield of juice depends primarily on the
cultivar's degree of pulpiness. Other factors influence yield
such as the stage of ripeness, size of berries, seediness,
thoroughness of fermentation and efficiency of crushing,
pressing and other operations (Winkler et al . 1974).

Sampling
The most important source of variation is in the individual
vine (Rankine 1997). A detailed set of precautions is given
by Rankine to enable the most representative sample to be