In its simplest form, whole bunch means that when grapes are being fermented a portion of the grapes are left intact as whole bunches and fermented with the stems, stalks, and all! This is also sometimes called whole cluster.

There's a few reasons winemakers choose to incorporate whole bunch. It can create lighter, and sometimes brighter, colour in wines; or add more perfumed aromatics and extra complexity. It can add some herbal, spicy, or peppery notes, give the impression of extra freshness, or add sweetness. It also increases the pH of the wine, softening acidity.

On the palate, whole bunch can also change the feel and shape of the tannins. Since fermenting whole bunches includes the stems, it can impart a lot more tannins. This means grape varietals that are already very tannic are less suited to whole bunch.