The whole bunch fermentation question.

The whole bunch fermentation question.

Take some grapes, how you proceed from here depends on the style of wine that you want to make. Jamie Goode explores how decisions in the winery reflect in the bottle.

For reds, it’s all about extracting the colour and flavour compounds, and their precursors, from the skins. There are lots of ways of doing this.

Most modern wineries making larger volumes of wines will separate the grapes from the stems in a machine called a crusher/destemmer before fermentation. The whole bunches go in one end, and the stems are spewed out the other. The grape berries fall down and are often crushed a bit, to release some juice, as they fall into the hopper, which is emptied into a fermentation tank.

Fermentation begins and the grape skins float to the top. They are then either punched down to keep them wet and to aid in extraction of flavours, like stirring a tea bag, or juice from the bottom of the tank (the fermenting wine) is pumped over the top of the skins. After fermentation has finished, the juice is drained off, and the skins – which still contain quite a bit of wine – are pressed.

But of late, there has been a lot of interest in using a traditional method that had fallen out of favour a bit. It’s called whole bunch, or sometimes whole cluster, fermentation.

De-stemming Pinot Noir at Thousand Candles. [Photo Rick Liston] Punching down by hand.

What is whole bunch fermentation?

Like it sounds, when some or all of the grape clusters for a red wine aren’t destemmed prior to fermentation. There are many variations on this theme. There is some overlap here with a technique called carbonic maceration, which also involves fermentations with intact bunches of grapes. But the two aren’t necessarily the same thing.

Classic whole bunch fermentation was typically used for Pinot Noir in Burgundy, and - after a period where it went out of fashion - it is coming back.

Indeed, Pinot Noir is the red variety most closely associated with whole bunch, and wherever it is grown you will hear winemakers discussing whether they like whole bunch fermentation or not.

How is it done?

Typically an open-top fermenter will be filled with entire clusters of grapes. It’s common for these to be crushed or foot-trodden a bit, to release some juice to kick-start fermentation. If carbonic maceration is desired, then the grape berries will be left whole, without any treading, and the tank filled with carbon dioxide to flush out any oxygen. Then a series of enzymatic transformations take place that produce some alcohol, aromatic compounds, and also help leach colour from the skin. This accounts for the bright colour and fruity aromas you find in some Beaujolais, a region well known for this technique.

Any juice released from the grapes at the bottom will begin a normal alcoholic fermentation through yeast activity. Then, at a certain point, the grapes will be pressed. The resulting juice still has quite a bit of sugar left, so the remainder of the alcoholic fermentation will take place off the skins, resulting in a perfumed, lighter-styled red wine. If the whole bunch fermentation involves squishing some of the grapes first, there will be a bit of carbonic fermentation in intact berries, but at the same time there will be a yeast-driven alcoholic fermentation, and more extraction (of tannins) from the skins.

Foot treading grapes in a stone lagar at Viñedos de Alcohuaz in Chile. Treading by foot gently extracts colour from the skins

Shades of carbonic

The term ‘semi-carbonic’ gets thrown around a lot in tastings. There’s actually no such thing as fully carbonic in the sense that only a small amount of sugar is converted to alcohol in the process, but we generally mean that ‘full carbonic maceration’ allows the grapes to do their thing intact for around a week to ten days before pressing, before allowing alcoholic fermentation to complete once the still sweet juice is released from the berries. Semi-carbonic is usually when a portion of the grapes are crushed as well as leaving some intact, or where after a few days the bunches are foot trodden or punched down to release more juice and allow a standard alcoholic fermentation.

Why do whole bunch?

The resulting wines can be more aromatic, and taste fresher, and can also take some structure from the stems themselves. The paradox is that having the stems in the ferment actually raises the pH a little (the wine loses acidity) because of potassium present in the stems. This causes some of the acid to precipitate out as tartrates, sometimes seen as crystalline deposits inside fermentation vessels.

Rather than making the wine taste less fresh - which is what you’d expect from lower acidity - whole bunch reds usually taste juicier because of the different aromatics.

It’s quite common for winemakers to use a portion of whole cluster in their ferments. They might, for example, add a layer of whole bunches at the bottom, and then cover this with destemmed fruit. Or they might add lasagne-like alternating layers of bunches and berries. If someone says they used 20% whole cluster in a wine, then this could mean each fermenter had a fifth taken up with whole bunches, or it might mean that one of five fermenters was entirely whole cluster. The distinction here is important, because an entirely whole cluster ferment will be quite different to a partial whole cluster ferment.

Another advantage of whole bunch is that the presence of stems helps with fermentation dynamics: the fermentation is often longer, and doesn’t get as hot, which can be an advantage.

Are there any disadvantages?

Some winemakers don’t like whole cluster ferments, because they feel it adds extraneous flavours to the wine that don’t come from the terroir. There’s also the widespread belief that stems add greenness or herbal notes to the wine. This may be true in some cases, but many winemakers are happy working with green stems, while others insist on them being liginified) or fully ‘ripe’. It could be that the greenness only becomes a problem when the ferment is managed too roughly, for instance by punching down too much. Nonetheless, some winemakers munch on the stems – tasting them – before they decide whether to do a whole-bunch fermentation or not.

If whole bunch isn’t done well the wines can taste a bit austere as the stems can add tannic structure. If it is done carelessly, another issue can be the growth of acetic acid bacteria that cause volatile acidity. See our article on understanding wine faults for more on VA.

As well as being popular with Pinot Noir, it is also used commonly with Gamay, and sometimes with Syrah. It is less common with the Bordeaux red grape varieties because the likes of Merlot, Cabernet Sauvignon and Cabernet Franc already have green notes as part of their aroma profile, and winemakers aren’t keen to add to this. Generally speaking though, whole bunch is attracting increasing interest as a winemaking technique, and it is particularly common in natural winemaking or where producers are working in a more traditional or ‘low-intervention’ way in the cellar.

Winemakers who use whole bunch