Macrowine 2021
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

Related articles…

Influence of weather and climatic conditions on the viticultural production in Croatia

The research includes an analysis of the impact of weather conditions on phenological development of the vine and grape quality, through monitoring of four experimental cultivars (Chardonnay, Graševina, Merlot and Plavac mali) over two production years. In each experimental vineyard, which were evenly distributed throughout the regions of Slavonia and The Croatian Danube, Croatian Uplands,

Teasing apart terroir: the influence of management style on native yeast communities within Oregon wineries and vineyards

Newer sequencing technologies have allowed for the addition of microbes to the story of terroir. The same environmental factors that influence the phenotypic expression of a crop also shape the composition of the microbial communities found on that crop. For fermented goods, such as wine, that microbial community ultimately influences the organoleptic properties of the final product that is delivered to customers. Recent studies have begun to study the biogeography of wine-associated microbes within different growing regions, finding that communities are distinct across landscapes. Despite this new knowledge, there are still many questions about what factors drive these differences. Our goal was to quantify differences in yeast communities due to management style between seven pairs of conventional and biodynamic vineyards (14 in total) throughout Oregon, USA. We wanted to answer the following questions: 1) are yeast communities distinct between biodynamic vineyards and conventional vineyards? 2) are these differences consistent across a large geographic region? 3) can differences in yeast communities be tied to differences in metabolite profiles of the bottled wine? To collect our data we took soil, bark, leaf, and grape samples from within each vineyard from five different vines of pinot noir. We also collected must and a 10º brix sample from each winery. Using these samples, we performed 18S amplicon sequencing to identify the yeast present. We then used metabolomics to characterize the organoleptic compounds present in the bottled wine from the blocks the year that we sampled. We are actively in the process of analysing our data from this study.

The use of rootstock as a lever in the face of climate change and dieback of vineyard

As viticulture faces challenges such as climate change or vineyard dieback, the choice of the variety and rootstock becomes more and more crucial. To study rootstock levers in the Bordeaux region, a parcel of Cabernet Sauvignon (CS) was planted with four rootstocks in 2014. Twenty repetitions of each of the following four rootstocks were set up: 101-14 MGt, Nemadex AB, 420A MGt and Gravesac. The number of bunches, yields and pruning weights of the vine shoots were measured individually on 240 vines from 2017 to 2021. Since 2020, nitrogen status assessed by assimilable nitrogen level, hydric status assessed by δ13C and berry maturity were measured on 80 samples taken from 20 repetitions of the four rootstocks. A lower yield was measured for CS grafted onto Nemadex AB due to the lower number of bunches and the lower weight of berries. The differences between the other three rootstocks are small, but CS grafted onto 420A MGt was the most productive. The CS grafted onto Nemadex AB had the lowest pruning weight while 101-14 MGt had the highest. In 2020, δ13C showed a more moderate water stress with 101-14 MGt and 420A MGt than with Nemadex AB. Surprisingly, the Gravesac was under more stress than the 101-14 MGt. The nitrogen status in the berries was better for Nemadex AB but this was perhaps due to the significantly lower weight of the berries.Rootstock 101-14 MGt attained the highest accumulation of sugars in the berries while 420A MGt allows to preserve higher acidity. The parcel is still young which may explain some of the results. These measures must therefore be continued over the next several years to fully assess the effects of these rootstocks on the development of the vines and the quality of the production under new climatic conditions.

Analysis of some environmental factors and cultural practices that affect the production and quality of the Manto Negro, Callet and Prensal Blanc varieties

45 non irrigated vineyards distributed in the DO (Denomination) Pla i Llevant de Mallorca and the DO Binissalem Mallorca were used to investigate the characteristics of production and quality and their relationships certain environmental factors and cultural practices. The grape varieties investigated are autochthonous to the island of Mallorca, Manto Negro and Callet as red and Prensal Blanc as white. All plants were measured for four consecutive years in the main production and quality parameters. Among the environmental factors, the type of soil has been studied, more specifically its water retention capacity, the planting density, the age of the vineyard and the level of viral infection. The presence or absence of virus seems to have no effect on any component studied in the varieties studied. For the white variety Prensal Blanc age is negatively correlated with production and the number of bunches, nevertheless it does not cause any effect on the required quality parameters. However, for the red varieties Callet and Manto Negro, the age of the plantation is the variable that best correlates with the quality parameters, therefore the old vines should be the object of preservation by the viticulturists and winemakers in order to guarantee its contribution to the quality of the wines made with these varieties.

Pruned vine biomass exclusion from a clay loam vineyard soil – examining the impact on physical/chemical properties

The wine industry worldwide faces increasing challenges to achieve sustainable levels of carbon emission mitigation. This project seeks to establish the feasibility of harvesting winter pruned vineyard biomass (PVB) for potential use in carbon footprint reduction, through its use as a renewable biofuel for energy production. In order to make this recommendation, technical issues such as the potential environmental impact, chemical composition and fuel suitability, and logistical challenges of harvesting biomass needs to be understood to compare with the results from similar studies. Of particular interest is the role PVB plays as a carbon source in vineyard soils and what effect annual removal might have on soil carbon sequestration. A preliminary trial was established in the Waite Campus vineyard (University of Adelaide) to test current management strategies. Vines are grown in a Eutrophic, Red Dermosol clay loam soil with well managed midrow swards. A comparison was undertaken of mid-row treatments in two 0.25 Ha blocks (Shiraz and Semillon), including annual cultivation for seed bed preparation, the deliberate exclusion of PVB (25 years) and incorporation of PVB (13 years) at an average of 3.4 and 5.5 Mg/Ha-1 for Shiraz and Semillon respectively. In both 0-10cm and 10-30cm soil core sample depths, combined soil carbon % measures in the desired range of 1.80 to 3.50, were not significantly different between treatments or cultivars and yielded an estimated 42 Mg/ha-1 of sequestered soil carbon. Other key physical and chemical measures were likewise not significantly different between treatments. Preliminary results suggest that in a temperate zone vineyard, managed such as the one used in this study, there is no long term negative impact on soil carbon sequestration through removing PVB. This implies that growers could confidently harvest PVB for use in several end fates including as a bio fuel.