WINETECH Technical Yearbook 2021

TRIAL 1: COMPARING SO 2 , GSH AND IDY PRODUCTS MATERIALS AND METHODS Machine harvested Sauvignon blanc grapes from three different sites located in the Marlborough region in New Zealand were used in the study. Small scale experiments were conducted and five treatments were applied in the juice phase prior to pressing: 1. 30 mg/L SO 2 (Control). 2. 100 mg/L GSH. 3. 30 mg/L SO 2 + 100 mg/L GSH. 4. 30 mg/L SO 2 + 30 g/hL of IDY product A. 5. 30 mg/L SO 2 + 30 g/hL of IDY product B. The juices were inoculated with Lalvin EC- 1118 and fermented to dryness. RESULTS: GLUTATHIONE CONTENT • Results showed that the wines made from grapes to which 30 mg/L SO 2 + 100 mg/L GSH was added, had by far the highest GSH content measuring between 80 and 120 mg/L GSH. • Compared to the above treatment (30 mg/L SO 2 + 100 mg/L GSH), the wines made from grapes to which 100 mg/L of GSH was added alone, had much

also not included in the European Union list of authorised oenological compounds). However, commercial inactivated dry yeast (IDY) products naturally rich in GSH have been developed and are allowed with conditions for use during winemaking. For more information, please consult the respective regulations. PRESERVE FRUITY VOLATILE THIOLS New Zealand researchers recently con­ ducted two studies to investigate the effect of antioxidant additions to Sauvignon blanc must on the chemical composition of the resulting wines (Lyu et al ., 2021). The main antioxidant under investigation was GSH, however, the use of inactivated dry yeast preparations, sulphur dioxide (SO 2 ) and ascorbic acid were also included for comparison. The study mainly focussed on the effects on 3MH and 3MHA concentrations. In part one of this two-part article, the effect of the addition of antioxidants, sulphur dioxide and GSH, as well as two commercial inactivated dry yeast products, are discussed. In part two, the effect of varying concentrations of GSH, as well as the addition of ascorbic acid, will be reported. TESTING THE EFFICIENCY OF ANTIOXIDANTS TO FORM/

less residual GSH with typically half (and for one site a quarter) of the added concentration still present in the wine. • The control samples (to which only SO 2 was added) contained very little (< 10 mg/L) GSH. • The addition of either IDY products to juice before pressing did not deliver wines with increased GSH content and the concentrations were not significantly different from the control samples. RESULTS: 3MH AND 3MHA CONTENT • Results showed that the wines made from grapes to which 30 mg/L SO 2 + 100 mg/L GSH was added, had, again, by far the highest 3MH and 3MHA concentration. For these wines, 3MH concentration ranged from around 3 000 to 4 000 ng/L. 3MHA concentrations measured around 750 to 1 300 ng/L. These are significant amounts and will undoubtedly have a sensory effect on the wine. • For two of the three wines, the treatment del ivering the second highest volatile thiol content was the controls (30 mg/L SO 2 only) measuring around 2 500 and 450 ng/L for 3MH and 3MHA, respectively. For these two wines, the thiol content in the

100 mg/L GSH treatment was about half the concentration found in the corresponding control samples. This would suggest that the antioxidant effect of 30 mg/L SO 2 was occasionally greater than the protective effect of 100 mg/L GSH. • The addition of IDY products did not result in wines with elevated volatile thiol content under the condition of this study. The 3MH and 3MHA concentrations were significantly lower for the IDY treatments when compared to the control. It should be noted that the products were added to the juice phase (just before pressing) and not right before fermentation as recommended by the suppliers. A different outcome could have been possible if suppliers’ recommendations were followed. CONCLUSION The results from trial 1 would suggest that the addition of SO 2 is more effective in preserving the volatile thiols compared to adding GSH alone. However, adding a combination of GSH together with SO 2 was the most effective and should be considered. The two commercial IDY products tested in this study showed little impact on wine

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