Chapter 6

Wine Fermentation

Whole-Cluster Fermentation for Red Wines

Whole-cluster fermentation (aka whole-bunch fermentation) refers to the fermentation of intact clusters of grapes that have not undergone destemming or crushing. Destemmed and/or crushed berries are then generally placed on top, and as the fermentation progresses. When grapes are left on the stems, the berries are often kept fully intact, which allows fermentation to begin on the inside. This is known as ultra-cellular fermentation, and is brought on by the enzymes in the berries, instead of yeast.

Sensory Effects

The most important sensory differences between wholecluster fermentation and conventional wines made from destemmed grapes are phenolic profiles and wine aroma. During the period when the berries remain attached to the pedicels, it is possible that enzymatic reactions, similar to those of carbonic maceration, will occur.

Grape Varieties

The technique is most commonly applied to Pinot Noir and Syrah, with the proportion of whole bunches used in Pinot Noir being as high as 100 percent, but with 15 to 20 percent being more common, especially with Syrah (Godden, 2018a). Pinot Noir is a relatively low-tannin grape variety and, therefore, can lack the broader, silky mouthfeel and the tannins as provided as in other red varieties. Whole-cluster fermentation can improve the mouthfeel in Pinot Noir.

Harvest

Although it is generally referred to as a stem, it consists of the pedicel, with the berries attached to it, the central axis or rachis to which the pedicels are attached and the peduncle where the bunch is cut from the shoot. Together these parts of the stem are 2 to 5 percent of the bunch mass. The appearance of the stem changes during ripening from green to brown due to lignification, which also has an influence on the chemical composition of the stem.

Whole-Cluster Fermentation Techniques

As the name suggests, whole-cluster fermentation describes a red winemaking technique where intact bunches of grapes are placed on the bottom of the fermentor, with destemmed inferior fruit placed on top. The premium fruit is allowed to pass the sorting table as whole bunches and the inferior fruit is destemmed and sorted. However, some winemakers prefer to place the whole bunches on top of the berries. Multiple factors are crucial when determining the percentage of whole-cluster grapes to use, which includes the ripeness of the grapes, the degree of lignification of the stems, and the presence of rot on the grapes.

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