 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

Impact of climate variability and change on grape yield in Italy

Viticulture is entangled with weather and climate. Therefore, areas currently suitable for grape production can be challenged by climate change. Winegrowers in Italy already experiences the effect of climate change, especially in the form of warmer growing season, more frequent drought periods, and increased frequency of weather extremes.
The aim of this study is to investigate the impact of climate variability and change on grape yield in Italy to provide winegrowers the information needed to make their business more sustainable and resilient to climate change. We computed a specific range of bioclimatic indices, selected by the International Organisation of Vine and Wine (OIV), and correlated them to grape yield data. We have worked in collaboration with some wine consortiums in northern and central Italy, which provided grape yield data for our analysis.
Using climate variables from the E-OBS dataset we investigate how the bioclimatic indices changed in the past, and the impact of this change on grape productivity in the study areas. The climate impact on productivity is also investigated by using high-resolution convection-permitting models (CPMs – 2.2 horizontal resolution), with the purpose of estimating productivity in future emission scenarios. The CPMs are likely the best available option for this kind of impact studies since they allow a better representation of small-scale processes and features, explicitly resolve deep convection, and show an improved representation of extremes. In our study, we also compare CPMs with regional climate models (RCMs – 12 km horizontal resolution) to assess the added value of high-resolution models for impact studies. Further development of our study will lead to assessing the future suitability for vine cultivation and could lead to the construction of a statistical model for future projection of grape yield.

VineyardFACE: Investigation of a moderate (+20%) increase of ambient CO2 level on berry ripening dynamics and fruit composition

Climate change and rising atmospheric carbon dioxide concentration is a concern for agriculture, including viticulture. Studies on elevated carbon dioxide have already been on grapevines, mainly taking place in greenhouses using potted plants or using field grown vines under higher CO2 enrichment, i.e. >650 ppm. The VineyardFACE, located at Hochschule Geisenheim University, is an open field Free Air CO2 Enrichment (FACE) experimental set-up designed to study the effects of elevated carbon dioxide using field grown vines (Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon). As the carbon dioxide fumigation started in 2014, the long term effects of elevated carbon dioxide treatment can be investigated on berry ripening parameters and fruit metabolic composition.
The present study aims to investigate the effect on fruit composition under a moderate increase (+20%; eCO2) of carbon dioxide concentration, as predicted for 2050 on both Riesling and Cabernet Sauvignon. Berry composition was determined for primary (sugars, organic acids, amino acids) and secondary metabolites (anthocyanins). Special focus was given on monitoring of berry diameter and ripening rates throughout three growing seasons. Compared to previous results of the early adaptative phase of the vines [1], our results show little effect of eCO2 treatment on primary metabolites composition in berries. However, total anthocyanins concentration in berry skin was lower for eCO2 treatment in 2020, although the ratio between anthocyanins derivatives did not differ.
[1] Wohlfahrt Y., Tittmann S., Schmidt D., Rauhut D., Honermeier B., Stoll M. (2020) The effect of elevated CO2 on berry development and bunch structure of Vitis vinifera L. cvs. Riesling and Cabernet Sauvignon. Applied Science Basel 10: 2486

Spatial determination of areas in the Western Balkans region favorable for organic production

In problematic conditions for production of grapes and wine caused by the COVID-19 pandemic and the resulting occurrence of wine surpluses, producers are increasingly turning to the innovative viticulture and winemaking of products that are more appealing to the market and the consumers. On the other hand, consumption of the food safety or organic products, and therefore of organic grapes and wine, is increasingly common in the world, in particular in Europe. The Regional Rural Development Standing Working Group (SWG RRD), as a regional intergovernmental organization gathers actors in the viticulture and winemaking sector from states and territories of the Western Balkans (South-East Europe) in the Expert Working Group for Wine, with the aim of improving viticulture and winemaking in this region through joint activities. In accordance with the aforementioned, the SWG RRD is working on advancing organic production of grapes and wine, and on recognition of specificities of the terroir of wine-growing areas in Western Balkans. In addition, as part of the project “Facilitation of Exchange and Advice on Wine Regulations in Western Balkan Countries” helmed by the German Federal Ministry of Food and Agriculture, in addition to harmonization of relevant legislation with EU regulations, efforts are being invested towards recognition of organic wines. Within activities and project implemented by this organization, expert analyses and scientific research of the terroir of Western Balkans were carried out, and some of the results are presented in this paper.

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Vineyards and clay minerals: multi-technique analytical approach and correlations with soil properties

Purpose of this research is to quantitatively assess the mineral component of vineyard soils, with particular attention to the mineralogical analysis of clays, which represent an element of high importance in the vineyard culture as well as in general agriculture. An X-ray diffraction (XRD) / thermogravimetric (TG) multi-technique analytical approach was developed, tested on soil samples taken from vineyards around the world. This codified analytical procedure was necessary to obtain precise qualitative and quantitative mineralogical data, globally comparable to distinguish the geopedological identity of the vineyards. Soil samples from vineyards of various locations were analysed, in very different geological conditions. The bulk-rock quantitative phase analysis (QPA) was obtained by the Rietveld method while the detailed composition of the clay-sized fraction was determined by modelling of the oriented X-ray diffraction patterns. The research provided a precise classification of the mineral component of soils, distinguishing the mineral phases of the clays and the so-called mixed-layer clay minerals. We found that the content in mixed layers can be directly correlated with the water retention and the cation exchange capacity of the soil, while the presence of other clayey minerals and phyllosilicates in this research did not affect this CEC parameter, which codes the fertility level of the soils. The study demonstrates that terroir, in particular soils formed in complex or very different geological conditions, can only be effectively interpreted by properly analysing its mineral phases, in particular the mixed-layer clay component. These are characteristic abiotic ecological indicators, which may have specific eco-physiological influences on the plant.