OENO IVAS 2019 banner
IVES 9 IVES Conference Series 9 Importance of matrix effects (wine composition) on protein stability tests of white and rosé wines

Importance of matrix effects (wine composition) on protein stability tests of white and rosé wines

Abstract

The presence of unstable proteins in wines can affect their stability and clarity. Before bottling, winemakers need to be sure that the wine is stable. A large number of stability tests have been proposed, usually based on heating a sample with a specific time-temperature couple. In practice, none is effective to accurately assess the risk of instability. Moreover, the interpretation of the results of these tests changes according to the region. 

The aim of this work is to compare, on 55 wines (4 vintages, 7 varieties, 5 areas), the most common heat test (30 minutes at 80°C) with the turbidity measured after 15 days at 35 °C on bottled wines. Proteins were analyzed in 33 cases. In addition, 10 wines were heated at 40 °C/30 min, 40°C/4 hours, 35 °C/15 days and 80 °C/30 min and the residual proteins analyzed. 

The results show no correlation between turbidity after heat test 80 °C/30 min and after 15 days at 35 °C. For some wines, especially Gewurztraminer ones, turbidity after heating at 80 °C can reach 330 NTU without any visual haze at 35 °C (< 3 NTU). Similar results are obtained when the heat test is performed after adjustment of pH to 3.4. The turbidity after heat test 80°C/30 min increases with pH, particularly above 3.6, which is not so unusual for Gewurztraminer wines. The pH effect is less significant at 40 °C. Finally, pH values alone cannot explain the different behaviors of wines. 

On the other hand, protein composition in wines depends on their pH. Thaumatin Like proteins (TL) 19 kDa, TL 22kDa and Invertases are present in almost all wines. Half of them contains Lipid Transfer Protein (LTP) and only a few Chitinases and β-Glucanase. These proteins are present when pH is lower than 3.5, probably because low pH favor Chitinase and-glucanase conformational changes and precipitation. 

Protein analysis after heating these various wines at different time-temperature couples led to this ranking: 
Chitinases are sensitive at low temperature (40 °C) and resist better at pH 3.7; 
TL 22kDa are sensitive, especially in Rosé wines; 
TL 19kDa are more stable, but their sensitivity depends on the pH; 
Invertase unfold between 60 and 80°C but is not affected by the pH; 
LTP can resist up to 80 °C. 

Turbidity after usual heat test 80 °C/30 min increases with total proteins concentration and pH. This is not observed after 15 days at 35 °C or 4 hours at 40 °C. These tests may be better to evaluate the actual risk of instability after bottling.

Related articles…

Evaluation of the enological potential of red grapes in southern Brazil

The Campanha Gaúcha is located in the pampa biome and has unique characteristics, as it is the hottest producing region with the lowest volume of rain in Southern Brazil. Furthermore, the large extensions of flat or low-sloping areas, harsh winters and great sunshine during the ripening period, made this the second largest producer of fine wines in Brazil.

Sensory profile: a tool to characterize originality of wines produced without sulfites

A trend to reduce chemical inputs in wines exists, especially sulfur dioxide (SO2). This additive is widely used due to its antioxidant, antiseptic and antioxidasic properties. During without sulfites vinification, bioprotection by adding yeast on harvest could be a sulfites alternative. With extension of this wine market, sensory impact linked to sulfites absence and/or sulfites alternative should be evaluated. That’s what this approach proposes to do, focusing on sensory characteristics of wines produced with or without SO2 addition during the winemaking process. METHODS: Wines were elaborated from Merlot grapes of two maturity levels according to three modalities: SO2, without SO2 and bioprotection on harvest (mix of Torulaspora delbrueckii and Metschnikowia pulcherrima). SO2 modality was sulfited throughout the winemaking and aging processes whether other modalities received any addition. After two years of aging, sensory studies were carried out with a specific panel for one month. First, descriptors were generated to differentiate the wines, then panelists were trained on these specific descriptors for five sessions and finally wines sensory profiles were elaborated

Grape ripening delaying with combined use of leaf removal and natural shading in Manto negro (Vitis vinifera L.) under deficit irrigation

The increasing frequency of heat waves during grape ripening presents challenges for the production of high-quality wine grapes. This underscores the significance of developing effective irrigation and canopy management techniques to optimize both yield and grape quality.
A field experiment was carried out during 2021 and 2022 using Manto negro wine grapes to study the effect of two irrigation strategies and different light exposure levels on grape quality. In a four-block experimental vineyard at Bodega Ribas in Mallorca, two irrigation treatments—moderate and severe deficit irrigation—were implemented. Within each irrigation plot, three light exposure treatments were randomly assigned, encompassing exposed clusters from pea size, non-exposed clusters, and shaded clusters after softening.

Effect of ozone application for low-input postharvest dehydration of wine grapes

The postharvest dehydration of grapes is a traditional practice to obtain wines with unique traits (e.g., sweet, dry/reinforced).

Towards more coherent rules for alcohol labelling in the European Union

In its 2020 beating cancer plan, the european commission announced plans for mandatory warning signs for alcoholic beverages. However, no concrete legislative proposal has been put forward so far. Instead, ireland passed national legislation in 2023 that requires warning signs for all alcoholic beverages from 2026. Despite significant effects for the common market, the eu commission did not this challenge this law in the so-called tris notification procedure. We argue that the commission’s inaction is consistent with the case law of the european court of justice: in the absence of harmonized rules, member states have a large margin of discretion to enact national health measures.