Grape stems in Pinot noir production: To add or not to add?

Abstract

To produce high quality Pinot noir wine, the extraction of tannins and methoxypyrazines (MPs) is pivotal. This study delves into their development in Pinot noir grape tissues and explores extraction management through whole bunch fermentation practices. Tannin concentration was determined by methyl cellulose precipitation method and the mean degree of polymerisation was determined using HPLC analysing tannin units after phloroglucinolysis. Aroma compounds, including MPs, were identified and quantified by GC-MS. Analysing two Pinot noir clones, AM10/5 and UCD5, revealed distinct tannin and MP development patterns. AM10/5 exhibited higher seed and stem tannin levels but lower MP levels than UCD5 at harvest. Stem MPs increased towards véraison and then decreased towards harvest, while skin MPs remained consistently at low or undetectable levels. This study also found that grape stems exhibited the highest tannin extractability (64%-78%), which explains the significant increase of tannin concentration in whole bunch fermentation treatments. Comparing whole bunch fermentation of two clones, AM10/5 grapes produced wines with higher concentration of tannins and MPs, and darker colour. High proportion of whole bunch addition significantly increased the concentration of MPs in wines made from both clones, which contribute to the enhanced green and vegetative characters in resultant wines. This research provides valuable insights for winemakers to make informed decisions to produce high-quality Pinot noir wines.