What’s the deal with whole bunch ferments?

Freshly picked Pinot Noir whole bunches

Most red wines today are made from destemmed grapes. The advantages with varieties like Cabernet Sauvignon which are already prone to green flavours from an excess of pyrazine are obvious, but destemming had strong advocates even in Burgundy, notably Henri Jayer, who fiercely opposed stems and influenced many winemakers away from their use. At the time this was associated with a positive improvement in the wines away from the then, not uncommon, greenness and rusticity.

Modern crusher destemming machine in action

Today however, it is no longer a question of either staying with tradition or embracing the benefits of modern destemming. The use of whole bunches has become a conscious and calibrated winemaking decision, most particularly with Pinot Noir or Syrah. One key reason for this is global warming. Together with better yield management, warmer climates mean riper stems. And it’s no longer an either/or decision. While ferments can still be 100% whole bunch or 100% destemmed, increasingly the winemaking practice is to include a portion of whole bunches in the ferment and there are various ways of doing so. 

What are the benefits of including whole bunches? I still remember the first ever barrel tasting I did with Hugh Crichton, then at Vidal, now at Elephant Hill, where tasting Syrah I was astonished to find that the while bunch barrels which I expected to have firmer tannins, were actually softer and silkier. They also had a distinctively pronounced aromatic profile that was both more spicy and more floral. These are two of the known benefits – an inclusion of whole bunches in the ferment for Syrah or Pinot Noir adds a textural smoothness and elevated aromatic profile.  A third important benefit is an element of freshness and elegance contributed from the stems. Ripe stem tannins are notably more subtle than oak tannin. Coincidentally and perhaps paradoxically, inclusion of stems increases the supply of potassium in the ferment which reduces acidity due to the precipitation of potassium tartrate, but the despite this reduction in acidity, whole bunch included wines usually taster fresher and juicier.

The presence of stems in the ferment has another benefit – it slows the fermentation speed and thus reduces the temperature of the ferment as well. There are several variables here: apart from what proportion of whole bunches are included there is also the question of how they are included. One method is to layer whole bunches and destemmed grapes like lasagne. Another is to put the whole bunches in the bottom. Yet another is to put them in the top. Particularly with the latter, the cap is more aerated, allowing some fermentation heat to escape. But in any of these scenarios the use of stems creates a more aerated, freer draining marc. Whole bunch inclusion results in wines with slightly lower alcohol, which may also be an important element for freshness, especially in hotter years. This is because stems contain water but not sugar. Offsetting this of course is the need to pick late to ensure stem ripeness, which means likely higher sugar levels in the grapes and thus higher alcohol.

There will be different sensory results from the different whole bunch placements in the ferment. Retaining the intact bunches at the top does make the rate of extraction slower and easier to monitor than when they are placed beneath crushed berries. The pressing mechanics are also impacted. During pressing the stems act like a colander enhancing the flow of juice through the skins and seeds which can make the press easier and faster.

The inclusion of whole bunches in a ferment means by default uncrushed whole berries are also included. In any whole bunch ferment then, there are potentially three different environments which give rise to two different fermentations. There will be largely intact clusters of grapes in a Carbon Dioxide (CO2) rich environment which undergo auto fermentation or carbonic maceration in the absence of oxygen. There are grapes crushed at the bottom of the tank, whether simply from the weight of the mass above or by mechanical or manual means (such as foot stomping), which undergo yeast fermentation in contact with skins, seeds and stems. And there are intact grapes surrounded by fermenting must, which will first undergo auto fermentation but as they break up during this process will then continue with yeast fermentation.

CO2 may be added by dry ice, gas sparging or simply produced by yeast fermentation of crushed berries. Being heavier than oxygen, it displaces it. Without going into all the chemistry, carbonic maceration produces alcohol more slowly and produces more glycerol. Up to half of the malic acid is metabolised to other acids and ethanol without accumulation of lactic acid. Volatile compounds such as ethyl cinnamate and others are produced giving strawberry, raspberry cherry and kirsch aromas. Lower oxygen also limits the oxidation of fatty acids that normally lead to production of compounds with vegetal or tomato-leaf aromas and flavours. The displacement of oxygen by CO2 in the third environment limits the operation of aerobic yeasts such as acetobacter from producing acetic acid or ethyl acetate. It is clear then, that with a whole bunch ferment, carbonic maceration may have a significant part to play alongside the influence of stems.

Over the last decade or so, the benefits of freshness, elegance and possibly lower alcohol have proved attractive even to some Bordeaux producers struggling with hotter years. Since around 2015 there has been some experimentation with whole bunches in the Merlot and Cabernet Franc at Chateau Carmes Haut-Brion and Smith Haut-Lafite, also at Berliquet and Chateau Le Puy. The question under consideration is whether careful use of stalks can help preserve some elegance and freshness in hotter vintages.

There are disadvantages in using whole bunches as well. The most obvious is that if the stems are anything less than well lignified and fully ripe, there is a risk of adding harsh green characters. Another side-effect, regardless of stem ripeness, is the tendency of the stems to absorb anthocyanins from the wine, leaving it paler and more translucent. There is a less well-known corresponding benefit however: that same binding of anthocyanins with tannin creates more stable molecules that are less prone to subsequent fading. So, this polymerisation process both causes initial reduction in colour but improves subsequent colour stability. This is an important attribute for many Pinot Noir producers – fixing or stabilising the colour can improve the wine’s appearance as it ages.

Colour Intensity from Three Different Ferments of Petit Verdot

It will be evident from the above, that use of whole bunches in fermentation really does require careful consideration by the winemaker of several variables. Larry McKenna, one of the pioneers of Martinborough Pinot Noir was known for his use of whole bunch and I asked his successor winemaker at Escarpment, Tim Bourne about their use.

“For Escarpment, whole bunch use with our Pinot Noirs has intrinsically been a part of our winemaking since the beginning”, Tim advised. “Our founder, Larry McKenna spent time at Domaine Dujac, who are famous proponents of whole bunch. I also have a fondness for it from my time making Shiraz in the Barossa Valley, where we were one of the few at the time extensively using whole bunch. At Escarpment, we use more as you head up the range of wines we produce. Essentially, we are using it to add layers to our wines, particularly the single vineyards. We believe it helps us to express our site. It does bring tannin, but that is not the end game for us, we like it for the perfume it adds to the wine and the shape it brings to the palate, along with the added complexity.”