Spring Mountain's goal is for 100% removal of grape stems at the crusher. They do not want the bitterness or astringency that might be extracted from bits of this stem material during fermentation. Their small Delta crusher-stemmer does about as well as any crusher they have seen in separating the berries from the stems.
The quantity of berries that are not crushed during stem removal and during conveyance to the fermenter is a factor they watch closely and vary by vineyard and variety. The quantity of whole berries affects extraction of tannins in a inverse relationship. This quantity is controlled at between 50% and 80% whole berries depending on the situation. The blocks that they expect to be most astringent are crushed less.