The cluster or bunch is the section of the vine where berries are attached.

At budbreak, a shoot begins to grow that will eventually produce small flowers. After flowering occurs, grapes will develop at the location of each flower. Cluster size and shape vary greatly depending on the varietal of grape, vine health and weather.

If the stems of a cluster have become lignified, some red wine producers choose to include a portion or all of the stems during fermentation. This technique is most commonly employed with Pinot Noir grown in locations where the grapes have had a chance to fully mature. Whole cluster fermentation, if performed correctly, is believed to impart more complexity into the final wine. The inclusion of stems helps stabilize fermentation temperature and color while imparting earthy stem tannins into the wine.

It should be noted that, if stems haven’t fully ripened, they will release “green” tannins which will make the wine taste bitter or impart unpleasant vegetal characteristics.