 IVES 9 IVES Conference Series 9 Are my bubbles shrinking? A deeper look at oxygen desorption in wine

Are my bubbles shrinking? A deeper look at oxygen desorption in wine

Abstract

In the past decade, there has been an increasing amount of work dedicated to understanding micro-oxygenation in wine. Oxygen desorption into nitrogen gas is a similar process, but there has been little work focusing on this process and no work explicitly examining the effect that changes in wine components have on the process. The removal of excess dissolved oxygen from wine prior to bottling is commonly done in winemaking. A widely used method involves sparging nitrogen through the wine, in a process known as desorption. An indicator of the rate of oxygen desorption is the oxygen volumetric mass transfer coefficient (kla), which can be determined experimentally. The aim of the study was to examine how temperature, superficial gas velocity, and ethanol and glycerol levels affected the kla of dissolved oxygen into nitrogen gas in an aqueous solution of ethanol and glycerol. For the experiment, ethanol and glycerol concentrations were varied between 9 and 15% v/v, and 5 and 25 g/L respectively. The temperature was varied between 10 and 20C. The superficial gas velocity was varied between 0.15 and 0.32 cm/s. The experiments were performed in a 15L bubble column with a stone sparger. Before each run, the column was sparged with air in order to saturate the solution. Nitrogen was sparged until the concentration of oxygen was below 0.1 mg/L. DO levels were measured with an oxygen probe. The mean bubble size was determined using a high speed camera. The results showed that in the ranges tested, ethanol and glycerol concentration had no effect on the kla. A strong correlation was shown between superficial gas velocity, temperature and the kla The kla varied between 0.0139 and 0.0236s^-1. It was expected that the varying ethanol and glycerol concentrations would have an effect as the physico-chemical properties changed. Consequently an experiment was done in which ethanol concentration was incrementally increased from 0 to 10% v/v. It was found that raising the ethanol concentration to 0.1% increased the kla significantly relative to water. Beyond this the kla did not increase significantly. It was found that at ethanol concentrations of 0 to 0.02% the mean bubble size was nearly 2 times greater than at 0.05%. This suggests that the rise in kla is as a result of smaller bubbles. Preliminary tests performed on white wine showed that the kla was lower than in the ethanol/glycerol solutions under the same conditions. The kla range was 0.0094 and 0.012 s^-1 at 10 and 20 C respectively. The use of an aqueous solution of ethanol and glycerol overestimates the oxygen desorption rate in wine. This indicates that other unexamined properties within wine have a significant effect on kla. Oxygen desorption is significantly improved with the introduction of 0.05 % ethanol. Examining how wine proteins, acids and phenols affect the oxygen kla may give a better estimate of the desorption process in wine.

DOI:

Publication date: September 7, 2021

Issue: Macrowine 2021

Type: Article

Authors

Steven Sutton

Stellenbosch University,Prof. Wessel Du Toit, Stellenbosch University Prof. Robbie Pott, Stellenbosch University

Contact the author

Keywords

oxygen desorption, wine processing, volumetric mass transfer coefficient, nitrogen sparging, wine sparging, micro-oxygenation keyword3)

Citation

The combined effects of climate, soils, and deficit irrigation on yield and quality of Touriga Nacional under high atmospheric demand in the Douro Region

Global warming is one of the biggest environmental, social and economic threats in several viticultural regions. In the Douro Valley, changes are expected in the coming years, namely an increase in temperature and a decrease in precipitation. These changes are likely to have consequences for the production and quality of wine.
The aim of this study was to explore the effects of different soil characteristics combined with several deficit irrigation strategies, managed throughout ETc references and predawn leaf water potentials thresholds, on physiology, yield, and qualitative attributes on the Touriga Nacional variety under years of mild to severe water and heat stress.
The studies were conducted over seven years (2015 to 2021) in two plots of a commercial vineyard located at Quinta do Ataíde (Symington Family Estates) planted in 2011 and 2014 at 170 meters elevation, growing under three water regimes: non-irrigated (NI) and two deficit irrigation strategies (30% and 60% ETc) assessed weekly by Ψpd. The site has an annual rainfall below 500 mm, with high atmospheric demand. Climate data was collected from a weather station, located on site. Berry ripening was followed weekly for fruit analysis. At harvest, yield, vigour and pruning weight per vine were determined from 90 vines by treatment. Each season at veraison the NDVI Index was accessed by a drone. The soils physic-chemistry in the experimental blocs were analysed and grouped by SWHC. Delta C-13 analyses were also performed per treatment in two years.Irrigation had a positive effect on yield per vine, mostly due to an increase in berry and cluster weight, and fertility index through the years. A significant increase in sugar content, colour and phenols was observed with deficit irrigation in some years, but vine vigour related to soil characteristics had by far the greatest impact on quality.

Mapping and tracking canopy size with VitiCanopy

Understanding vineyard variability to target management strategies, apply inputs efficiently and deliver consistent grape quality to the winery is essential. However, despite inherent vineyard variability, the majority are managed as if they are uniform. VitiCanopy is a simple, grower-friendly tool for precision/digital viticulture that allows users to collect and interpret objective spatial information about vineyard performance. After four years of field and market research, an upgraded VitiCanopy has been created to achieve a more streamlined, technology-assisted vine monitoring tool that provides users with a set of superior new features, which could significantly improve the way users monitor their grapevines. These new features include:
• New user interface
• User authentication
• Batch analysis of multiple images
• Ease the learning curve through enhanced help features
• Reporting via the creation of colour maps that will allow users to assess the spatial differences in canopies within a vineyard.
Use-case examples are presented to demonstrate the quantification and mapping of vineyard variability through objective canopy measurements, ground-truthing of remotely sensed measurements, monitoring of crop conditions, implementation of disease and water management decisions as well as creating a history of each site to forecast quality. This intelligent tool allows users to manage grapevines and make informed management choices to achieve the desired production targets and remain profitable.

Bioclimatic shifts and land use options for Viticulture in Portugal

Land use, plays a relevant role in the climatic system. It endows means for agriculture practices thus contributing to the food supply. Since climate and land are closely intertwined through multiple interface processes, climate change may lead to significant impacts in land use. In this study, 1-km observational gridded datasets are used to assess changes in the Köppen–Geiger and Worldwide Bioclimatic (WBCS)

Diagnosis of soil quality and evaluation of the impact of viticultural practices on soil biodiversity in a vineyard in southwestern France

Viticulture is facing two major changes – climate change and agroecological transition. In both cases, soil quality is seen as a lever to move towards a more sustainable viticulture. However, soil biological quality is little considered in the implementation of viticultural practices. Gascogn’Innov (2017-2022) is an Operational Group funded by the European Innovation Partnership for Agriculture. As such, it brings together winegrowers from the south-west of France, scientists, advisors and technicians, around a project focused on viticultural soil biological functioning and the design of technical routes more respectful toward soil heritage. To achieve this, the project aims to acquire references on the impact of viticultural practices on soil biology from a dynamic way, and to test a methodology to integrate information provided by the soil bioindicators to manage farming systems. A set of indicators of soil biological quality are evaluated in the project: microorganisms (bacteria and fungi abundance and diversity), fauna (abundance and diversity of nematodes and earthworms), physico-chemical characteristics, soil structure assessment and degradation rate of organic matter. Based on a network of 13 plots that have been subject to an initial diagnosis in 2017, several agronomical practices to restore soil fertility are experimented to redesign the cropping system (for instance plant cover, organic matter inputs, reduction of herbicides, mineral fertilizers). System redesign was made in collaboration by winegrowers and an interdisciplinary group of experts (agronomists, biologists). Several indicators are measured on vine and soil at each vintage to assess vine health and productivity. At the end of the project (2021), a final diagnosis was carried out. Gascogn’Innov allowed to create a regional database on the quality of wine-growing soils, which permitted to evaluate the effect of practices according to soil types. Especially, decreasing the intensity of tillage and increasing the duration and diversity of grass coverage tends to increase the abundance of all the organisms studied. This project confirmed the value of soil biological quality indicators to drive the sustainability of practices, but also highlighted the key-role of expertise, in both agronomy and soil biology, to help winegrowers understand and appropriate their soil quality diagnoses.

Different soil types and relief influence the quality of Merlot grapes in a relatively small area in the Vipava Valley (Slovenia) in relation to the vine water status

Besides location and microclimatic conditions, soil plays an important role in the quality of grapes and wine. Soil properties influence…