 IVES 9 IVES Conference Series 9 Inhibition of reductive characters in wine by cu-organic acids: predicting the duration of protection

Inhibition of reductive characters in wine by cu-organic acids: predicting the duration of protection

Abstract

Cu organic acid complexes efficiently bind hydrogen sulfide in wine and therefore prevent its accumulation and subsequent reductive off-flavour [1]. This fraction of Cu can also bind methanethiol, the other main contributor to reductive wine characters, albeit with less efficient binding than for hydrogen sulfide [1]. However, during bottle aging of wine, the concentration of Cu organic acid complexes gradually decline and the sulfide-bound form of Cu increases. The point at which the Cu organic acid concentration is depleted signifies a potential for reductive aroma development to occur. The aim of this study is ascertain how long Cu organic acid complexes in wine can offer a protection against the reductive aroma compounds. High (0.6 mg/L), medium (0.3 mg/L) and no (0 mg/L) Cu(II) additions were made to Pinot Grigio and Chardonnay wines at bottling, and the bottled wines were then stored at 14 °C in darkness. Analysis was performed on the wines at 0, 2, 4, 8 and 12-14 months after bottling. Throughout bottle ageing process, the concentrations of three different Cu fractions, attributed to Cu organic acid complexes, Cu thiol complexes and sulfide-bound Cu, were monitored by stripping potentiometry and colorimetric methods. The free and salt-releasable concentration of hydrogen sulfide and methanethiol were determined by gas chromatography with chemiluminescene detection. Sensorial analysis was also performed on the wines after 12 months. During the first 2-months of bottle aging of all wines, the Cu-organic acid concentrations initially remained stable or increased, as total packed oxygen was consumed. Afterwards, during the low oxygen aging phase of the wines, the Cu-organic acid concentration declined exponentially with a concomitant increase in sulfide-bound Cu. These changes in sulfide-bound Cu were matched by an increase the salt-releasable hydrogen sulfide concentrations of the wines during aging. Free concentrations of hydrogen sulfide and methanethiol were only found to accumulate in wines without any Cu-organic acid present at bottling. For the Pinot Grigio without Cu-organic acid present at bottling (i.e., the no Cu addition treatment), the free methanethiol concentrations in the wine were above the aroma threshold and this wine was assessed as reductive. Alternatively, for the Pinot Grigio with Cu-organic acid complexes at bottling, only concentrations of free methanethiol below the aroma threshold were measured and the wine was not reductive. The decay in Cu-organic acid complexes, in the low oxygen aging phase of the wines, were found to follow first order kinetics that were similar for the Chardonnay and the Pinot Grigio. These results enable determination of the time-frame that Cu-organic acids can offer white wine protection against the potential accumulation of reductive aroma compounds.

DOI:

Publication date: September 14, 2021

Issue: Macrowine 2021

Type: Article

Authors

Xinyi Zhang

National Wine and Grape Industry Centre, Charles Sturt University, Wagga Wagga, Australia,Nikolaos KONTOUDAKIS (Laboratory of Enology and Alcoholic Drinks, Department of Food Science and Human Nutrition, Agricultural University of Athens) John W. BLACKMAN (National Wine and Grape Industry Centre, Charles Sturt University) Andrew C. CLARK (National Wine and Grape Industry Centre, Charles Sturt University)

Contact the author

Keywords

cu organic acid complexes, hydrogen sulfide accumulation, white wine bottle ageing

Citation

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.

Local adaptation tools to ensure the viticultural sustainability in a changing climate

[lwp_divi_breadcrumbs home_text="IVES" use_before_icon="on" before_icon="||divi||400" module_id="publication-ariane" _builder_version="4.19.4" _module_preset="default" module_text_align="center" module_font_size="16px" text_orientation="center"...

Inhibition of Oenococcus oeni during alcoholic fermentation by a selected Lactiplantibacillus plantarum strain

The use of selected cultures of the species Lactiplantibacillus plantarum in Oenology has grown in prominence in recent years. While initial applications of this species centred very much around malolactic fermentation (MLF), there is strong evidence to show that certain strains can be harnessed for their bio-protective effects. Unwanted spontaneous MLF during alcoholic fermentation (AF), driven by rogue Oenococcus oeni, is a winemaking deviation that is very difficult to manage when it occurs. This work set out to determine the efficacy of one particular strain of Lactiplantibacillus plantarum(Viniﬂora® NoVA™ Protect), against this problem in Cabernet Sauvignon must. The work was carried out at commercial scale and in a winery environment and compared the bio-protective culture with the more traditional approach of reducing must pH by the addition of tartaric acid. The combination of both was also investigated. The concentration of both Oenococcus oeni and Lactiplantibacillus plantarum was determined using qPCR. The adventitious Oenococcus oeni showed the most growth during AF in the control wine, whereas in the wines treated with Lactiplantibacillus plantarum a bacteriostatic effect against this species was observed. This effect was comparable to the wines treated with tartaric acid. This has particular commercial relevance for controlling the flora in musts with high pH, or when the addition of tartaric acid is either not permitted or is prohibitive for other reasons.

Effects of graft quality on growth and grapevine-water relations

Climate change is challenging viticulture worldwide compromising its sustainability due to warmer temperatures and the increased frequency of extreme events. Grafting Vitis vinifera L.

Ecophysiological performance of Vitis rootstocks under water stress

The use of rootstocks tolerant to soil water deficit is an interesting strategy to cope with limited water availability. Currently, several nurseries are breeding new genotypes, but the physiological basis of its responses under water stress are largely unknown. To this end, an ecophysiological assessment of the conventional 110-Richter (110R) and SO4, and the new M1 and M4 rootstocks was carried out in potted ungrafted plants. During one season, these Vitis genotypes were grown under greenhouse conditions and subjected to two water regimes, well-watered and water deficit. Water potentials of plants under water deficit down to < -1.4 MPa, and net photosynthesis (AN) <5 μmol m-2 s-1 did not cause leaf oxidative stress damage compared to well-watered conditions in any of the genotypes. The antioxidant capacity was sufficient to neutralize the mild oxidative stress suffered. Under both treatments, gravimetric differences in daily water use were observed among genotypes, leading to differences in the biomass of root, shoot and leaf. Under well-watered conditions, SO4 and 110R were the most vigorous and M1 and M4 the least. However, under water stress, SO4 exhibited the greatest reduction in biomass while M4 showed the lowest. Remarkably, under these conditions, SO4 reached the least negative stem water potential (Ψstem), while M1 reduced stomatal conductance (gs) and AN the most. In addition, SO4 and M1 genotypes also showed the highest and lowest hydraulic conductance values, respectively. Our results suggest that there are differences in water use regulation among genotypes, not only attributed to differences in stomatal regulation or intrinsic water use efficiency at the leaf level. Therefore, because no differences in canopy-to-root ratio were achieved, it is hypothesized that xylem vessel anatomical differences may be driving the reported differences among rootstocks performance. Results demonstrate that each Vitis rootstock differs in its ecophysiological responses under water stress.