We draw these conclusions about the dependence of composition on size and irrigation:
- Imposing significant water deficits can decrease berry size and increase skin: juice ratio by approximately 25%compared to conventional irrigation regimes. From two separate yield experiments, it appears that smaller berries are not produced when yields are increased from 3.5 to over 10 tons/acre by leaving longer spurs at pruning.
- Berry size is highly correlated with seed mass/berry. However, berry growth did not keep pace with seed growth such that the amount of seed per unit berry mass increased with berry size. Low irrigation had less effect on seed growth than on mesocarp growth for any size of berry. Hence, Low irrigated fruit had greater relative seed mass, implying a greater concentration of seed tannin in the resultant wines.
- The mass of skin tissue bore a constant relation to berry size, i.e. the mass of skin per unit berry mass was relatively constant over the 3-fold range of berry sizes encountered. Low irrigated fruit had greater relative skin mass per berry. Low irrigation inhibited mesocarp growth more than skin growth such that the relative amount of skin per unit berry mass was always greater than for Control and High irrigated fruit.
- The amount of skin tannin per berry was a fairly constant fraction of berry size. Thus, the concentration of skin tannin in must was only slightly lower for large fruit than for small fruit (approximately 10%). However, the concentration of skin tannin was significantly greater in Low irrigation fruit of any size (approximately 30% greater in Low fruit).
- The amount of anthocyanin per berry increased with berry size, but was a slightly decreasing fraction of berry size. The resulting anthocyanin concentration was approximately 20% less from the largest fruit compared to small fruit. Again, the concentration was significantly greater (approximately 30%) in Low irrigated fruit for all fruit sizes.
These results show that the amount of each skin solute is not a constant that is diluted to varying degrees dependent upon fruit growth. Accumulation of skin solute is coordinated with growth. Accordingly, oft observed changes in fruit composition caused by water deficits are not attributable simply to differences in berry growth. There is an independent effect of deficit irrigation on composition. Because deficit irrigation produces lower yield, it is important to evaluate whether there is an independent effect of yield on these quality parameters. The fruit size and irrigation differences in fruit composition were carried through to the resulting wines. The differences in wine composition were slightly less dependent upon fruit size than the juice composition, suggesting a possible difference in “extractability”. And, both fruit and wine composition were much less sensitive to fruit size than the theoretical dependence that is predicted from differences in surface: volume of the berries. A preliminary investigation found differences among the low, control and high irrigation wines in the intensities of green beans aroma, red fruit by mouth, bitterness and astringency as shown below. When wines were made from different sized berries that were irrigated similarly, small berry wines were more astringent than large berry wines.