Winemaking treatment – whole bunch fermentation

Whole-bunch fermentation describes a red winemaking technique where intact bunches of grapes are placed in the fermenter, rather than the grapes being de-stemmed and/or crushed.

Background

The technique is most commonly applied to Pinot Noir and Shiraz, with the proportion of whole bunches used in Pinot Noir sometimes as high as 100%, but with 15% to 20% being more common, especially with Shiraz. Use of the technique is not common with Cabernet Sauvignon and related varieties, because the high methoxypyrazine concentration in the grape stems can result in ‘cut grass’ and ‘herbal’ characters in the wine. In previous winemaking trials with Pinot Noir and Shiraz both 50% and 100% whole bunch were trialled, with all wines being well received by workshop participants.

Application and helpful hints

The biggest risk with the use of whole bunches is the extraction of ‘grassy’ and ‘herbal’ aromas and flavours, and overly astringent tannins from the grape stems. The best results are achieved when bunches with highly lignified (woody rather than green) stems are used. The most well-lignified stems are likely to be found in relatively low-vigour sections of the vineyard, because lignification commences when shoot growth stops. Consequently, lignification tends to be lower in wet years, especially when there is mid-to-late-season rainfall which stimulates vine growth, and in high-vigour vineyards. Lignification is also likely to be lower in cool-climates and in cooler years.

It is most common for the intact bunches to be placed on the bottom of the fermenter, with destemmed and/or crushed berries placed on top. However, some winemakers prefer to place the whole bunches on top of crushed berries because they feel it makes the extent of extraction from the stems easer to monitor, and note that greater extraction from the stems occurs when whole bunches are fully submerged. Thus, for instance, a 20% whole bunch inclusion will result in different sensory outcomes depending on whether they are placed on top of or underneath crushed berries. Regardless of where they are placed, as the fermentation progresses, the intact bunches are often partially or wholly crushed by plunging, or traditionally by foot-treading.

Even with ‘100%’ whole bunch fermentations, many winemakers will ensure that there is some liberated juice in the bottom of the fermenter. When it starts to ferment, either through yeast-inoculation or spontaneously, the CO2 produced will help to protect the remainder of the fruit from oxidation until full fermentation commences.

For several reasons, greater consistency in sensory outcomes is achieved with greater experience using the technique. For instance, during fermentation it is very difficult to obtain a representative sample to conduct sensory assessment, and therefore visual inspection becomes more important. Some winemakers take note of colour changes in the stalks as an indicator of optimal extraction, and may decide to press before fermentation is complete. Making a photographic record of stalks at various stages during fermentation may be useful for improving control and consistency in subsequent fermentations and seasons.

During pressing the stems act as drainage channels through the mass of skins and seeds, which means that musts containing whole bunches generally press very easily and quickly. However, this can also mean that during pressing, a sudden change from positive to negative sensory characters can occur, and for this reason it is important to continually taste from the press tray to identify if there is a change to ‘grassy’ and ‘herbal’ aromas and flavours or overly astringent tannins.

At pressing a substantial quantity of sugar may be liberated from intact berries, and it is therefore important not to allow the wine to cool down dramatically during and after pressing, in order to avoid stuck fermentation.

Practical and logistical considerations

Getting the whole bunches into the fermenter and then getting the skins seeds and stalks into a press at the end of fermentation are the largest logistical challenges, and without specialised equipment this can become labour-intensive. When filling presses using a hopper, ‘bridging’ of the stems often occurs, so it is advisable to tip slowly into the hopper, and to have long-handled tools such pitchforks on hand.

Potential risks

Due to the risk of ‘green’, ‘grassy’ and ‘herbal’ aromas and flavours and overly astringent tannins, it is advisable to take a cautious approach when trialling whole-bunch fermentation, by only using a small percentage of whole bunches at first (10- 15%) and assessing the results over time. It is also advisable to only make a small amount of whole bunch fermented wine in the first instance, which can then be blended into other batches of wine to the point where the desired sensory effects are achieved.


Resources

Goode, J. 2012 and 2016. Stemming the tide. World of Fine Wine.

Godden, P. Understanding whole-bunch fermentation. 2018. Aust. N.Z. Grapegrower Winemaker (652) : p. 63.

Godden, P.W. 2018. Spotlight on whole bunch fermentation. AWRI Technical Review 234: 12-15.