Aim of the study

The aim of this study was to determine the chemical and sensory effects of co-fermentation and post malolactic fermentation (MLF) blending of Shiraz (Syrah) with selected Rhône white cultivars. Co-fermentation of Shiraz is a traditional practice and in the Côte Rôtie appellation of the Rhône for instance, co-fermentation of Shiraz with up to 20% of Viognier is permitted. One of the aims of co-fermentation is to promote long term colour stability through co-pigmentation. Co-pigmentation is the formation of an interaction (or stacking) between flavonols and anthocyanins to form polymeric pigments. Polymeric pigments are more stable than monomeric anthocyanin during bottle ageing. Some white cultivars, such as Viognier, is reportedly richer in flavonols and co-fermentation could therefore theoretically increase colour stability. This is not necessarily always the case as certain studies have proved.

Two additional aims of co-fermentation is to increase acidity and aroma intensity of Shiraz wines. Co-fermentation can however be difficult to manage logistically since the two cultivars to be co-fermented do not necessarily ripen at the same time. Blending of final wines after MLF provides an easier alternative and its efficacy is evaluated in this study.

 

Project layout

  • Research was conducted in California and most of the grapes came from the Paso Robles area.
  • Marsanne and Roussanne grapes were harvested on 12 September 2016 and kept in cold storage (5°C) until processing.
  • Shiraz, Viognier, Picpoul and Grenache blanc grapes were harvested on 19 September 2016.
  • For the co-fermentation six treatments were carried out in triplicate: Shiraz control (SY) and SY plus 10% Viognier (VG), Marsanne (MR), Rousanne (RS), Picpoul (PC) or Grenache blanc (GB) solids (after pressing). The reason for the pressing is to minimise the dilution effect white grape pulp can have on final wine colour.
  • White grape solids were incorporate in the SY must with a gentle 30 seconds punch down. Sulphur dioxide (SO2), tartaric acid and diammonium phosphate (DAP) were also added.
  • Fermentation was conducted by EC 1118 between 19 and 27°C in 60 L food grade plastic containers.
  • After three days a Lactobacillus plantarum MLF starter culture (ML Prime) was added.
  • Fermentations received two punch downs of one minute each a day and total maceration time was 8 days.
  • For the post-MLF blending a portion of juice from each white cultivar was settled with 60 g/hL bentonite (Microcol CLG).
  • Alcoholic fermentation was conducted between 12 and 22°C. MLF was induced three days after crushing with the same MLF culture as the co-ferments.
  • SY wine was prepared the same as the control co-ferment wines and blending of this component and the white post MLF wines (10% by volume) was conducted in 20 L carboys in December 2016.
  • All wines were sulphured and bottled in January 2017.
  • The following analyses were conducted: basic wine analysis, spectrophotometric analysis and sensory analysis (descriptive analysis by a trained panel).

 

Main results

  • The treatments had very little effect on the basic chemistry of the wines. Only notable differences were the alcohol levels of three post MLF blended wines being higher than the rest: SY-MR, SY-RS and SY-PC.
  • Post MLF blended wines had higher anthocyanin glucosides, acylated anthocyanins and flavonols than co-fermented wines. This was still lower than the Shiraz control wines.
  • After 14 months of bottle ageing the major contributors to total pigment concentration of all wines were still the anthocyanin glucosides and acylated anthocyanins. Anthocyanin-derived pigments and polymeric pigments accounted only for 10 and 7% respectively.
  • Tannin concentrations were slightly higher in the co-fermented SY-VG, SY-RS and SY-MR wines, but in general the tannin concentrations in these wines were very low due to the small scale experimental design.
  • The co-fermented SY-VG wines were perceived as higher in citrus and cherry aromas than the control SY wine.
  • The SY-VG post MLF blended wine was perceived as higher in black fruit and cherry aromas than the control wine.
  • There were relatively little sensory differences between the rest of the wines. In both types of treatments the control wines (SY only) received the lowest sensory ratings for each attribute.
  • SY-VG post MLF received the highest sensory rating.

 

Significance of the study

This study indicated the possibility of post MLF blending instead of co-fermentation as a viable option to improve the colour and aromatics of Shiraz wines. Blending of wines is logistically easier to manage than co-fermentation. The study also found Viognier to be the better blending option compared to the other traditional Rhône cultivars tested. The limitations of the study, like most scientific studies, is that it was done on small scale under specific conditions. Only seven of the 11 treatments were also sensory analysed due to time and logistic constraints. Winemakers are encouraged to experiment comparing co-fermentation and blending.

 

Reference

L.F. Casassa, P.F.W. Mawdsley, E. Stoffel, P. Williams and J.C. Dodson Peterson (2020). Chemical and sensory effects of cofermentation and post‐malolactic fermentation blending of Syrah with selected Rhône white cultivars. Australian Journal of Grape and Wine Research: Vol. 26 (1), p. 41-52.  https://doi.org/10.1111/ajgw.12413

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This article first appeared on http://winetechscan.blogspot.com/