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  • How to better manage your wine shelf-life
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    Infowine in partnership with Vinventions invites you to a series of 3 webinars focused on the key parameters you need to monitor at different winemaking stages to optimize wine profile and its long...
    Published on: 10/18/2021

Smart Fining by Using Decision Support Tools

Vanille-Charlotte Achaintre, Céline Sparrow, Christine Pascal

SOFRALAB, 79 avenue Alfred Anathole Thevenet, 51530 Magenta, France
WQS, Vinventions Enology team, 7 avenue Yves Cazeaux, 30230 Rodilhan, France
The current study was executed in equal parts by both organizations.

The first quotations of wine fining can be found in documents dating from the 17th century. Milk, blood, egg whites and isinglass were then used as fining agents.

Since the outbreak of the Mad Cow disease in the 90’s, the demand for wines produced without animal origin additives and allergens has continually increased.

A selection of new alternatives  was created and tested by the Sofralab® group, who presented the project to the OIV in 1999 and 2006. Consequently, pea protein and yeast protein extracts became the base of new generation fining products. Today, Sofralab® is launching the Oenoterris® brand to satisfy an integrated agro-enological approach. The aim is to evaluate continuously both viticultural and enological practices in order to use the most suitable additive at the right time and at the correct dose. In winemaking, fining is one of the most important stages when it comes to using additives wisely.

The effects of fining must and wine are various:

  • Improved clarity
  • Sedimentation of solids and the speed at which they sediment
  • Colour management
  • Prevention or treatment of oxidative phenomena via polyphenol management
  • Improved sensory aspects

 

To conclude, fining has an important role in two major aspects which are clarification (clarity and sedimentation) and modification or elimination of components to improve the final wine quality (colour and polyphenol management, improved sensory quality).

For the first aspect which includes sedimentation and clarification, the results after fining can be measured in the winery, either visually or with the aid of a turbidimeter.

However, for polyphenol and colour management, parameters are more difficult to determine in the winery. In fact, they traditionally need to be measured with a spectrophotometer, which has some limitations, the main one being that the sample is no longer representative of the wine in the tank once it arrives at the laboratory. Furthermore, these measurements are not very accurate and the results are obtained several hours or days later, which means a quick decision at the winery cannot be made.

The need for reliable sensors, that are easy to use in the winery, that do not require sample preparation and which give immediate results, has become more and more important. For this reason WQS, the Vinventions enology service brand, is developing practical tools in order to measure parameters of interest directly at the winery and allow for faster decision making when necessary. This is the case for Polyscan to measure polyphenol concentration and Color to measure the chromatic characteristics of musts and wines.

In practice, there is not a perfect or ideal fining product. All have a mode of action that is more or less effective on each parameter. This is why it is fundamental to evaluate the must first and then determine the most important fining objective in order to choose the most suitable product as well as its dosage.

The research done by WQS over the last 10 years on polyphenols and colour allows for the musts to be characterized and sorted. This when coupled with SOFRALAB® expertise when it comes to enological products, allowed for the research to characterize the fining effects of different products and create a decision support tool to optimize must fining decisions in real time.

The remainder of this article presents the research behind this tool which is the result from the joint expertise of SOFRALAB® and WQS.

To begin, polyphenol concentration is related to future oxidation risk in white and rosé wines. The measurement of their content on site for musts and wines were developed using electrochemical methods and the utility of these measures in order to make decisions during the winemaking was subsequently determined (Ugliano et al. 2019, Pascal et al. 2020, Hastoy et al. 2020). The measurement by linear sweep voltametry, done with single use electrodes, consists in the application of increasing potential to the sample. At each level of potential, different components are oxidized and consequently electrons are freed which generates a current. The intensity applied vs the resulting potential (Figure 1) is a digital fingerprint of the oxidizable components found in the sample. This evolves throughout the winemaking process.

fig1

Figure 1: Example of intensity curve vs. potential obtained on a wine sample

To facilitate the interpretation of these results in real time and to help winemakers to make decisions, indexes are calculated by the equipment from this curve, in particular these two:

  • PhenOx: Total polyphenol content (in mg/L of gallic acid equivalents) in correlation with the Folin Ciocalteu index.
  • EasyOx: Easily oxidizable compounds, such as hydroxycinnamic acids, targets of polyphenol oxidase and also some native anthocyanins.

 

The measurements taken with Polyscan since 2014 make up a database of more than 40’000 measurements to this date. This database provides users with access to reference values, in particular average index values, according to grape variety and point during the winemaking process. This collaborative method allows for a quick ease of use of the equipment given that several vintages do not need to be studied for one user to have a reference to compare to.

The musts are then divided into 4 categories according to their PhenOx and EasyOx levels compared to the average of the grape variety being evaluated (Figure 2).

Médiane = Median

fig2

Figure 2 : Categorization of musts according to Polyscan measurements.

The musts that belong to each category correspond to grape types and harvest practices that are very variable.

In fact, the category “P+” corresponds to musts which are rich in polyphenols obtained from harvested grapes that are rich in polyphenols. Within this category there are musts from grapes where the vines suffered water stress or musts where extraction operations were used (machine harvesting, sulfite addition at crushing or pressing, maceration, high temperatures during harvest, high number of rotations during press filling and during pressing…). The last grape pressing fractions which are moderately rich in polyphenols can also be found in this category.

On the other hand, “P-” musts are poor in polyphenols, either because the grapes are naturally poor in polyphenols or because there was limited extraction during the processing.

The musts belonging to the “E+” category were protected from oxidation or are very little oxidized whereas the “E-” musts have already undergone an enzymatic oxidation.

Here is a generalized example of musts usually found in each category:

  • P-E+: Sauvignon blanc free run juice of grand crus from Bordeaux, in general musts with thiol rich profiles.
  • P-E-: bin must, highly oxidized, continuous press juice
  • P+E-: Chardonnay press must from warm terroirs
  • P+E+: Syrah rosé press must

 

Furthermore, must colour is linked with polyphenol extraction and their potential oxidation. It can be influenced by numerous parameters, such as sulfite addition, pH, etc. The measurement of the must colour can allow for an early correction of clarity and hue to obtain the desired result.

The measurement of chromatic characteristics, as defined by the International Commission on Illumination (CIE 1976) and revised by the OIV (OIV-MA-AS2-11 : R2006), provided information that is close to the colour sensations perceived by an observer.

These are the three characteristics:

  • Lightness, L*, which defines wine lightness
  • Hue, h°, that designated the colour: red, yellow…
  • Chroma, C*, which is linked to the more or less intensity of its colour.

 

In this reference, colours are represented in a sphere and each one is defined by three coordinates L*, C* and h° (Figure 3) or alternatively L*, a* and b*. The use of L*C*h° coordinated is preferred since this gives direct access to the sample colour according to to the hue (h°), which is more simple in terms of interpretation than when a* and b* parameters are used.

fig3

Figure 3: Colour location of a sample, perpendicular to the L*.
C* is the chroma (colour intensity from grey to intense) and h° is the hue (colour: red, orange, yellow, etc).

The use of a portable colorimeter, the Color P100, allows for a quick evaluation of the chromatic coordinates of a wine directly in the winery. The measurement is done using reflectance and can be done on samples directly without any particular preparation.

Furthermore, during the trials on musts presented below, a correlation was observed between the lightness and chroma of the samples (Figure 4): the samples with high lightness (the lightest) have a weak chroma (greyish). Therefore only the L* and h° coordinates will be used for the rest of the article, since they are sufficient for an initial approach and allow for a simplification of the reasoning and decision making at this stage of the process.

fig4

Figure 4: relationship between C* (chroma) and L* (lightness) of rosé must samples.

In practice, the fining of musts for colour reasons can modify the lightness of musts that are considered too dark or to eliminate brown pigments that are due to enzymatic oxidation. The L* and h° coordinates therefore characterize the must and allow for a fining decision to be made according to the desired colour. Must lightness increases when L* increases. The hue angle varies from 0° for red hues to 90° for yellow hues.

For rosé musts, a higher hue angle h° indicates that the must is more orange and therefore brown enzymatic oxidation pigments are present.

For white musts, the opposite is true, non-oxidized musts have a high angle hue (closer to yellow / green) and the presence of brown oxidation pigments would give a lower h° angle.

In the same way the musts are categorized with PolyScan, they can also be classified according to the colour system described below. Figure 5 shows the categorization of the white and rosé wines studied.
a)

fig5

 

b)

fig6

Figure 5: Categorization of musts according to hue h° and lightness L* for rosés (a) and whites (b)

Throughout this study more than 1600 fining methods were used on musts from 22 different grape varieties in France, in the laboratory and in the winery. For each trial, different fining products at different concentrations were used. PolyScan and Color measurements were taken before and after fining to characterize the effects of the different fining agents on must polyphenol concentration and colour.

The statistical treatment of these results allowed for the characterization of different fining agent impacts on different must categories and also the determination of a fining strategy for each of them.

In terms of polyphenol content, musts that are rich (P+ categories) must be treated with fining agents to reduce polyphenol content and prevent oxidation early. The sub-category P+E-, that have already undergone enzymatic oxidation, systematically need to have hue corrected.

The P- categories that are poor in polyphenols do not need to be treated with fining agents to reduce polyphenol concentration. However fining can correct hue, in particular for the P-E- category, which are oxidized musts.

The following provides some observations on colour, on white musts, where the main objective is to correct hue:

  • h°> 75° the must has a yellow-green hue and fining will have an impact only on L*, since the h° is already correct.
  • h°<75° the must has brown pigments, and fining can have an impact on h° that is variable according to the fining agent used.

 

On rosé musts:

  • L*<50 and h°<35°, these musts are dark red. Fining helps lighten the juice without modifying hue.
  • L*>50, the juice is light, fining has less impact on L* since it is already high, but will have an impact on h°.
  • The hardest category to treat are the light and orange hue musts (L*>50 and h°>35°) where carbon use is the only solution that can have a real impact on the hue.

 

These tests also showed that if the potential presence of brown pigments can be deduced from the must category determined by PolyScan, it is essential to measure the juice lightness in order to make a reasoned fining correction. In parallel, the presence of brown pigments linked with enzymatic oxidation does not indicate in any case that there is a low polyphenol concentration or that the must is sufficiently stabilized in terms of oxidation protection. Using both technologies is complementary in order to better evaluate the must and consequently decide the most suitable fining strategy. Table 1 summarizes the fining strategies for each PolyScan determined must category and the potential associated colour corrections.

fig7

Table 1 : Characterization of different must categories obtained with the aid of PolyScan

Furthermore, from these fining tests it was also possible to determine the sensory impact of each fining agent.

Tastings were done on the musts by comparing a non treatednon-treated control and each different fining method. The results showed that each fining agent had a specific impact and it was possible to identify in a bling blind tasting which fining agent was used. For example, KTS® Flot highly improved the mid-palate volume whereas Oenovegan® EPL has an impact on the length and corrects bitterness.

Trials done at the experimental winery of the SOFRALAB® group Group (Montagnac, 34, France) also showed that the specific fining impacts were also found during a blind tasting of the resulting wines. Two trials were done, one on a Sauvignon Blanc must and another on Grenache rosé. Six fining agents were tested during and after must sedimentation, each tank was then fermented in the same way. A “neutral” yeast was used in order to evaluate better the sensory impact of each fining agent. The wines were then bottles bottled and tasted by a jury of 25 enologists. These tastings confirmed the sensory impacts that were previously observed on the musts (Figure 6).

fig7

Figure 6 : Star graph of the average of each descriptor. Number of tasters: 25.

The impact was further observed upon analysis of ester type volatile compounds found in the wines (Figure 7).

fig9

Figure 7: Results of volatile compound quantification. Sum of esters in wine (mg/L)

A decision support tool to help choose a fining strategy was created based on the different PolyScan results. In the menu “sedimentation tank”, for each must measured, the application Smart App Collage suggests a fining agent and a dose to apply according to:

  • the fining objectives chosen by the user (clarification, sensory profile, colour)
  • the type of sedimentation (static or flotation)
  • other restrictions linked to the product objective (organic, vegan…).

 

It is also possible for the user to limit the fining choices according to the fining agents available at the moment.

To conclude, the results presented in this article, coupled with the practical expertise of the SOFRALAB® group Group enologists and the polyphenol and colour management knowledge of WQS, allowed for the creation of a fining support application that can be used directly in the winery.

This tool, together with the sedimentation tank menu of PolyScan, provides a recommended fining strategy using a measurement taken from the tank before fining and according to the fining objectives inserted.

The SMART APP’ COLLAGE allows for an instant measurement and quick decision making, directly from the tank and it is adapted for each kind of wine. The right product, at the correct dose and at the right time; the “best” additive. This tool is part of the Oenoterris® strategy which supports preventative and reasoned winemaking practices in order to valorize grape quality.

 

REFERENCES :

M. Ugliano, J. Wirth, S. Bégrand, J. B. Diéval, C. Pascal, S. Vidal, A novel electrochemical approach for rapid analysis of white grapes polyphenols and monitoring of pre-fermentative operations, Infowine 2019,

C. Pascal, N. Champeau, J-B. Diéval, S., An electrochemical method for real time measurement of polyphenols during winemaking, Infowine 2020,

X. Hastoy, S. Marquier, G. Blanc, C. Pascal, Utilisation de la voltamétrie linéaire de balayage pour déterminer la date de récolte de parcelles de Sauvignon Blanc, Revue des Œnologues (176), 2020, 44-46

Vocabulaire International de l'Éclairage. Publication CIE 17.4.- Publication I.E.C. 50(845). CEI(1987). Genève. Suisse.

Méthode OIV-MA-AS2-11 Détermination des caractéristiques chromatiques selon Cielab (Résolution Oeno 1/2006)

Published on 07/28/2021
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