The effects of grape stems and whole bunch fermentation on Pinot noir wine

by | Feb 28, 2022 | South Africa Wine Scan

Whole bunch fermentation is often used in the production of Pinot noir wines. The aim of this study was to compare different levels of stem inclusions and whole bunch fermentations on the phenolic and volatile aroma compositions of Pinot noir wines.



The harvested Pinot noir grapes (from New Zealand) had the following analysis: 23.4°Brix, 3.17pH, 9.33 g/l TA and 207 mg/l YAN.

The study comprised five different treatments:

  • Destemmed grapes with no stems (DS)
  • Destemmed grapes with 100% stems added back (DS100)
  • 70% destemmed grapes mixed with 30% whole bunches (WB30)
  • 40% destemmed grapes mixed with 60% whole bunches (WB60)
  • 100% whole bunches (WB100)

30 mg/L SO2 was added to the treatments, and the grapes were covered with CO2 and cold macerated for five days at 4°C. Grapes were then crushed and fermented with EC 1118 at 25 – 30°C. The cap was plunged twice a day initially and once a day at the end of maceration. After post fermentation maceration (four days) free run wines were collected, SO2 was added and after cold storage, wines were racked of the lees and bottled. Various analytical techniques were performed.



  • The inclusion of grapes stems and whole bunch fermentation increased tannin concentrations and decreased anthocyanin concentrations (likely due to the adsorption of anthocyanins on stems). However, WB30 had not impact on anthocyanin and tannin concentrations compared to the control.
  • WB100 had the highest tannin concentration
  • Adding 100% of stems or having a high proportion of whole bunches increased the chemical compounds responsible for woody and spicy characters, which are generally viewed as positive for wine quality. However, green characters, normally viewed as negative for Pinot noir quality, was also enhanced due to the extraction of methoxypyrazines from the stems (up to 7.63 ng/l).



The study indicates the significant effects of the inclusion of stems during Pinot noir fermentation on both the phenolic and aromatic characteristics of the wines. The effects can be both positive and negative for final wine quality and require a calculated balancing act from winemakers to achieve the optimum outcome.



Wimalasiri, P., Olejar, K., Harrison, R., Hider, R. and Tian, B. (2022), Whole bunch fermentation and the use of grape stems: effect on phenolic and volatile aroma composition of Vitis vinifera cv. Pinot Noir wine. Australian Journal of Grape and Wine Research.

Image copyright: Wikimedia

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