NOTES: Grape solids in white winemaking Since 2016 the Australian Wine Research Institute (AWRI) has made a series of wines from single batches of grapes, changing one variable in each fermentation, with the resulting wines being presented to winemakers in workshops around Australia. In 2019, the trial was conducted with Chardonnay. The AWRI’s Peter Godden covers key questions on grape solids in white winemaking and is the first in a series that will examine winemaking variables included in the 2019 trial that have a significant influence on Chardonnay wine style. Why are juice solids important? to characterise them, or to assess the aggregate to form larger particles, which In white winemaking, the degree of ideal inclusion rate to achieve a given then settle with the yeast lees. (Casalta et al. 2016). juice clarification is one of the first wine style. decisions a winemaker has to make, Alexandre et al. (1994) found that the What effects do solids have on with the quantity of juice solids affecting solids fraction of white juice contained fermentation? the primary and secondary fermentation about 70% polysaccharides and 8% Grape solids provide nutrients for yeast kinetics, and the sensory profile of the lipids, with the remaining material made cell development, particularly lipids and resulting wine. up mostly of minerals, pectin and about nitrogen. Lipids are integral components 2.5% nitrogen. It has also been reported What are juice solids? of cell membranes, which allow the cell to that phenolic compounds are present. tolerate the ethanol concentration found The solids content of juices varies Most grape-derived solids in white juice late in fermentation. Consequently, markedly, depending on the have a particle size less than 2µm in fermentations containing a greater characteristics of the grapes and the diameter, although once fermentation proportion of solids are generally faster processes used for juice extraction. commences the size of particles decreases, and less likely to become sluggish or However, the exact composition of juice possibly due to agitation caused by CO2. stuck. In addition, wines made with solids remains unclear and consequently Towards the end of fermentation, as CO2 high juice solids have a faster rate of there are no standardised methods production slows, the particles tend to malolactic fermentation. Keep up with market trends Ensure great taste, authenticity, and bioprotection with Viniflora® Specialty yeasts Learn more at www.chr-hansen.com or contact us at [email protected], +61 418 142 982 December 2019 – Issue 671 www.winetitles.com.au Grapegrower & Winemaker 73 NOTES: How can I measure the degree of solids turbidity, with higher turbidity resulting facilitate the production of the ‘struck in my juice? in lower volatile acidity and acetaldehyde flint’ reduction character prized in some concentrations, and increased glycerol. Chardonnay wines. Turbidity measurement, with results High solids have also been shown to expressed in nephelometric turbidity produce wines with lower concentrations For further information about grape units (NTU), is the most common way of esters and higher concentrations solids or other technical grapegrowing in which the degree of solids of a juice is of volatile sulfur compounds and or winemaking questions, contact the assessed, with total wet or dry suspended higher alcohols, resulting in subdued AWRI helpdesk on (08) 8313 6600 or solids or percentage solids also used. varietal character. [email protected] However, none of these measures characterise the composition or particle In one study, wines of three varieties Acknowledgements size of the solids present. Nonetheless, in made from high-solids juices contained more polysaccharides than wines Michael Downie is thanked for his a practical sense, NTU is the most useful made from low-solids juices, regardless assistance in finding and acquiring way to assess and compare the quantity of the extraction method (whole information resources used in the of solids in individual juices. bunch pressing, free-run juice or hard preparation of this article. Is there an ideal NTU for pressing). However, the results were not white winemaking? as clear for the phenolic content of the References and further reading wines. Although the wines made from Schneider (2013) (referenced in Casalta Alexandre, H.; Nguyen van Long, T.; Feuillat, high-solids juices generally contained et al. 2016) recommended NTUs M. and Charpentier, C. (1994) Contribution comparatively high concentrations à l’étude des bourbes: Influences sur la of 50 to 150 to ensure that yeast had of total phenolics, ratings of wine fermentescibitédes moûts. Rev. Fr. d’Oenol. access to sufficient lipids. However, astringency were not affected. However, 146:11-20. in fermentations with more clarified when the wines made from higher solids juice, the addition of oxygen at the juices were adjusted to the same pH as Casalta, E.; Vernhet, A.; Sablayrolles, end of the yeast growth phase can low-solids wines, they were rated higher J-M.; Tesière, C. and Salmon, J-M. (2016) Review: Chracterization and role of grape compensate for the lack of juice lipids, for ‘oiliness’ and viscosity, which was solids during alcoholic fermentation under with the yeast able to use the oxygen to attributed to higher polysaccharide and enological conditions. Am. J. Enol. Vitic. synthesise lipids. phenolic concentrations. Increases in 67(2):133-138. glycerol concentration of up to 1 g/L were An Italian study fermented juices of seen; the authors noted that while this Gawel, R.; Day, M.; Schulkin, A. and Smith, P. three white varieties at six turbidity might lead to an increased perception of (2015) Murky winemaking: How juice solids levels ranging from 15 to 350 NTU. sweetness, it would not affect perceived affect the macromolecular composition Greater turbidity resulted in shorter wine viscosity (Gawel et al. 2015). and mouthfeel of white wine. Wine Vitic. J. fermentations with lower residual sugar 30(6):18-22. concentrations, independent of yeast Are there dangers in using a greater assimilable nitrogen content. A turbidity quantity of solids? Nicolini, G.; Moser, S.; Román, T.; Mazzi, E. and Larcher, R. (2011) Effect of turbidity on of 100 NTU was considered the ‘best Most of the polyphenol oxidase enzymes fermentative volatile compounds in white compromise’ to maximise ‘fruit’ aromas which can cause juice browning in the wines. Vitis 50(3):131-135. while avoiding either sluggish ferments presence of oxygen are found in the grape at lower turbidity, or ‘reductive’ sensory skin, and therefore high-solids juices Smith, P. A. and Waters, E.J. (2012) characters observed at higher turbidity may be more susceptible to oxidation. Identification of the major drivers of (Nicolini et al. 2011). In addition, the concentration of any ‘phenolic’ taste in white wines. Final report to vineyard-derived elemental sulfur would GWRDC. Available from www.wineaustralia. What effects on wine composition and also increase with increasing solids com/research/search/completed-projects/ sensory properties have been related to content, with that sulfur potentially awr-0901 the concentration of juice solids? contributing to the formation of negative Schneider, R. (ed.) 2013. Les vins blancs The concentrations of at least 40 volatile ‘reductive’ characters in wine. However, de la démarche marketing à la vinification: and non-volatile compounds have been if managed correctly, the inclusion of Les clés d’un pilotage réussi. Paris: France shown to be affected by changes in juice a greater concentration of solids can Agricole. 74 Grapegrower & Winemaker www.winetitles.com.au December 2019 – Issue 671.