In recent years, studies have reported the positive influence of non-Saccharomyces yeast on wine quality. Many grape varieties under mixed or sequential inoculation show an overall positive effect on aroma enhancement. A potential impact by non-Saccharomyces yeast on volatile and non-volatile compounds should benefit the flavor of Riesling wines. Following this trend, four separate sequential fermentations (using the non-Saccharomyces yeasts Torulaspora delbrueckii, Metschnikowia pulcherrima, Pichia kluyveri, and Lachancea thermotolerans with Saccharomyces cerevisiae) were carried out on Riesling must and compared to a pure culture of S. cerevisiae. Sequential fermentations influenced the final wine aroma. Significant differences were found in esters, acetates, higher alcohols, fatty acids, and low volatile sulfur compounds between the different trials. Other parameters, including the production of non-volatile compounds, showed significant differences. This fermentation process not only allows the modulation of wine aroma but also chemical parameters such as glycerol, ethanol, alcohol, acidity, or fermentation by-products. These potential benefits of wine diversity should be beneficial to the wine industry.

To determine the effects of different processing steps, such as enzymatic treatment of the mash and pasteurization, on selected quality parameters, strawberries were processed to juices and purees. To identify the processing steps causing the highest losses, samples were taken after each step, and ascorbic acid, total phenols, anthocyanins, and antioxidant capacity were analyzed. To assess the antioxidant capacity, three different methods were applied: the trolox equivalent antioxidant capacity (TEAC), the ferric reducing antioxidant power (FRAP), and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, showing correlation coefficients of 0.889 to 0.948. The antioxidant capacity decreased with processing steps except heat treatment, which partly caused an increase due to the formation of antioxidant active products. The content of ascorbic acid, in comparison to that in the frozen strawberries, decreased significantly during the processing of the fruit to puree by 77%. In the pressed cloudy juices, the loss of ascorbic acid was 37%. The decline of phenolic compounds, measured as total polyphenols and anthocyanins, was smaller (between 30-40%). Pressing and pasteurization were the most critical steps for the decrease of these compounds. The enzymatic treatment of the mash within 90 min supported the release of secondary plant metabolites, while ascorbic acid is reduced up to 20%.

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Aim: This research was undertaken in the context of climate change and understanding how rising temperatures may interact with viticultural practices, used to manage fruit exposure in Riesling. An experimental system was designed to passively warm the bunch zone and separate the factors, heat and indirect heat by solar radiation.Methods and results:  Field experiments were conducted in 2016 and 2017 at an experimental site located near Rüdesheim in Germany. To increase bunch exposure compared to non-defoliated controls (CON), around 75% of the leaves were removed manually from the bunch zone in an early defoliation treatment at pea size (DEF_E; E-L 31) and later defoliation at véraison (DEF_L, E-L 35). An open heating system (OHS) was installed from pea size stage (E-L 31) onwards. Temperature, light penetration and canopy characterization were determined. Maturity measurements included determination of berry fresh weight, total soluble solids, available primary amino acids (N-OPA), pH, titratable acid and organic acids. For determination of the phenols, berry skin was freeze dried, extracted and analysed by HPLC-PDA.Compared to the same position in the control vine rows, the temperature was more than 10 °C warmer inside the chamber, around 5 °C warmer at the opening of the chamber and at the upper end of the bunch zone, up to 3 °C warmer on a day with high solar radiation. On overcast days there was no temperature difference between these treatments.The OHS treatment affected the ratio of malic and tartaric acid as well as the ratio of glucose and fructose, and produced smaller berries compared to both CON and DEF treatments. Phenols (flavanols, hydroxycinnamic acids, flavonols) in the berry skin were mostly affected by the defoliation. In both years, DEF_E had the highest amount of phenols, followed by the DEF_L. In 2016 OHS had nearly the same concentration of phenols compared to CON. In 2017, the concentrations of phenols were higher in OHS compared to CON.Conclusion: Under future scenarios of increasing temperature conditions, strong changes will be expected for berry maturity parameters. It was found that using an experimental setup to passively heat the bunch zone, malic acid was reduced, smaller berries were produced, and the glucose/fructose ratio changed. For the defoliation treatments, phenol concentrations in berry skin were strongly affected by defoliation and to a lesser extent by higher temperature. Basic maturity parameters were relatively unaffected by defoliation.Significance and impact of the study:  Riesling is known for its fruity character and the importance of the sweetness and acidity balance for determining wine style. Under warmer temperature conditions the acidity content will decrease through faster malic acid respiration, impacting the wine´s profile. Higher phenol content could lead to an astringent taste and together with higher protein content, may provide a risk of haze in wine. Neither effect is desirable. In this study, increased bunch exposure following defoliation had a greater effect than temperature alone on phenols. Therefore, the vineyard and canopy management practice will need to be adapted.