The example of an iconic Italian winery
The objective of this iconic winery is to provide the right dose of fining for Sauvignon Blanc musts. The technical director wants to avoid excessive fining in order to preserve the quality of the juice.
This winery carries out plot-by-plot selection of Sauvignon Blanc to obtain varietal thiol profiles. This selection starts in the vineyards with adapted winemaking practices (nitrogenous fertilising, absence of water stress, yield control, harvest date control, etc.) and continues in the cellars via a pre-fermentation route protected from oxidation.
The plots not included in the thiol selection are subject to a less protective process in the cellars. Among these non-selected plots, there are also plots that have been subject to hydric or thermal stress observed in the vineyards.
The different viticultural practices of the two groups of plots described above have an impact on polyphenol concentrations: the plots destined to produce varietal thiol profiles generally display relatively low polyphenol levels in the grapes. On the contrary, the plots that undergo stress generally display high levels of polyphenols, since these stresses encourage biosynthesis of polyphenols and their concentration through withering of the grapes.
Use of PolyScan to characterise the polyphenol content of juices
Analysis of polyphenols with the Polyscan were carried out on the settling vats:
- It includes the polyphenol content of the grapes as well as the impact of operations carried out before their introduction to the settling vats (harvesting, crushing, destemming, steeping that may be carried out, pressing, separating of the juices, transfer of juices to vats, transport that may be carried out, etc.).
- These are the values which are best to be used for making fining decisions.
The PhenOx index (concentration of total polyphenols) measured show a fairly high variability in the polyphenol concentrations of the different juices.
Measurement of the EasyOx (concentrations of easily oxidisable compounds, among which features caftaric acid, the target of polyphenol oxidases) makes it possible to highlight a higher level in juices intended for thiol profiles higher than the median, which is 30 for juice from Sauvignon Blanc settling vats), which reflects the technical process intended to protect from oxidation.
Adaptation of decision-making according to the must
In addition to the fact that the measured polyphenol concentration values are consistent with the viticultural and pre-fermentation process implemented, they also make it possible to take differentiated decisions to treat the polyphenols of each batch of grapes:
- No fining or limited fining for juice displaying PhenOx below the median value.
- Considerable fining for juice displaying PhenOx above the median value.
These measures make it possible to adapt the fining to the grape juice. The help to avoid excessive or inadequate fining, which, beyond the economic impact, is advantageous for the quality of the juice.