From traditional carbonic maceration and whole bunch inclusion to experimental stem layering and "baking", producers around the globe are employing various techniques to use stems in ferments.
Wine-Searcher spoke with seven winemakers around the globe to learn more about the integration methods, as well as the how, when, and why behind them all.
California-based winemaker Martha Stoumen explains that there are two principal ways of working with whole clusters. The first incorporates using uncrushed berries left on the clusters in sealed vessels – otherwise known as carbonic maceration – while the latter involves breaking the berries prior to and during fermentation via foot treading or pumpovers.
"The technique always depends on the specific lot of fruit – no parcel is treated the same way, and treatment of the same parcel can vary depending on the year," she says.
Additionally, Stoumen notes that vine age plays a big role in the success of whole cluster inclusion.
"A good rule of thumb is that old vines can handle whole cluster fermentations better because these vineyards often don't have the excess of potassium that younger vineyards can have," she says. Stoumen explains that younger vineyards can often experience too much of a pH shift with whole cluster fermentation, which can ultimately lead to a loss of freshness and/or stability.
Vessel-focused considerations
Jim Fischer and Jenny Mosbacher, founders of Willamette Valley-based Fossil & Fawn, also use the two above methods, and note that fermentation vessels play a huge role in the process.
"Our favorite whole cluster fermentations are done in insulated boxes, specifically those most commonly used in the fishing industry," Mosbacher says, citing that said boxes keep the bunches cool during the carbonic portion of fermentation, then build and hold heat nicely once the yeasts get to work. "This allows for the development of fresh fruity flavors initially and then gentle but thorough extraction by the end of primary fermentation,".
Fischer builds on this, stating that the insulative capacity of the material significantly impacts the final outcome in the wine.
"Insulated plastic allows for a cool, low-temperature carbonic fermentation initially; as the heat builds from yeast activity, more savory, spicy, earthy, and complex qualities are extracted," he says. Equally, Fischer describes wood as a good insulator, which he believes would have similar thermodynamics to his and Mosbacher's insulated bins. Although curious, the duo has not yet experimented with concrete or clay, though the two have a grasp on the meticulous care required to use them.
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"My understanding is that concrete and earthenware require diligent treatment with an acidic solution before use to leach positively charged ions from the material," he says. If not done properly, he explains, significant pH shifts and softening can happen within the wine. "As the stems already contribute to a pH shift, one would need to be cautious when using whole bunches in concrete or earthenware fermenters, or be prepared to add tartaric acid to the wine," he says.
Experimental whole-cluster techniques
Alban Debeaulieu, winemaker and head of winery at Abbott Claim in Oregon, reveals that in the past, he and his team have experimented with layering destemmed and whole cluster fruit within the same vessel, though have come to prefer classic methods of incorporation.
"In the end, we've ultimately gone back to the simple, old way of putting destemmed fruit at the bottom and whole clusters on top," he says. Debeaulieu notes that leaving stems at the bottom of the vessel can cause them to remain saturated in liquid, which in turn, results in a continuous – and often undesirable – extraction.
"On the contrary, stems up top will tend to dry-out during fermentation with heat, CO2, and alcohol vapors from fermentation, which mitigates their herbaceous profile and will only be extracted from when pumping-over or punching-down," he says. Additionally, Debeaulieu shares that he's heard of a few producers air-drying stems and reintroducing them to the wine.
"The idea here would be to polymerize stem tannins, therefore making them less reactive, less astringent, and to oxidize green aromas from stems," he explains, though affirms that he does not have experience doing this firsthand.
Partial cluster inclusion
Gonzalo Bertelsen, managing director and winemaker at Vinedos Organicos Veramonte/Neyen de Apalta in Chile, says that when using partial whole clusters, the best way to determine the optimal percentage is by good old-fashioned trial and error.
"We have done from 0 up to 100-percent whole cluster," he says, adding that the winery has found between 20 and 40 percent to be the sweet spot for Pinot Noir. "However, this all depends on the grape concentration, time to do it, labor, space available and the most important factor is the stalks' maturity," he explains.
To logistically achieve the desired percentage, Bertelsen says that the team will fill the tank with 40 percent destemmed fruit, then add 20-40 percent of whole bunch fruit on top of it. The rest of the tank is then topped with destemmed fruit. "The idea is to have three layers: destemmed, whole bunch, destemmed. We do not add stems back in," he says.
In the Côte Roannaise, Carine Serol uses a similar three-layer method to Bertelsen, though has noticed the opposite of Debeaulieu with regards to stem positioning.
"Some whole clusters at the bottom of the vessel can help the filtration of the juice for remontage," she says. Serol also cites the notion of vintage variation, stating that she tends to use a higher percentage of whole clusters during riper vintages.
Separate fermentations
Rather than mixing whole-cluster and destemmed fruit in the same vessel, Stoumen prefers to keep the fermentations separate, as she notes that the kinetics are different with each approach.
"Whole cluster favors cooler fermentations, and therefore more aromatic results, whereas destemmed favors warmer fermentations and therefore more full-bodied results," she says, adding that she'd rather blend lots down the line than mix two methods in the same vat.
"In the past [when mixing], I've gotten muted results that lack a strong aromatic voice and a strong textural voice," she reveals. In turn, Stoumen reveals that her experimentations mostly lie in the realms of fermentation time, as well as how much she is or is not working the cap. "It's always a balance between trying to create ethereal aromatics, not over-extract tannins, and also build midpalate," she says.
Like Stoumen, Mosbacher and Fischer have experimented with mixing whole cluster and destemmed fruit in the same vessel, and have also found that they prefer to keep things separate.
"The processing of destemming detaches the fruit from the pedicel, creating an opening in the fruit, which allows for more juice to be initially released into the vessel," says Fischer, stating that said juice presence makes initial yeast fermentation both faster and hotter. "In the past when we have added whole cluster fruit into a destemmed lot, the high heat earlier on in the fermentation extracted much more woody flavors and aromas from the stems into the wine than we'd liked," he reveals.
On the contrary, Fischer says that whole cluster lots have little to no juice the first few days of fermentation (until the combination of carbonic maceration and the weight of the fruit mass begins to break down the skins and release liquid into the bottom of the vessel), which allows for a very cool and gentle extraction of stem and skin tannins.
"By the time the ferments hit their peaks (which can be two weeks or more from their pick dates), the tannins are more fully integrated into the wine and no bitterness is extracted," Mosbacher says. "We have experimented with other methodologies, but have found that vinifying 100-percent destemmed lots and 100-percent whole-cluster lots in isolation allows us greater understanding of each fermenter's character, which then informs how we proceed in elevage."
Stoumen echoes this, stating that beginning with high-quality fruit is key, and that separate fermentations allow her to make decisions based on how to feed the microbial population as a means to get the flavors and textures she wants from the grapes.
Pros and cons
When well executed, Debeaulieu states that whole clusters can bring textural and aromatic dimensions that participate to greater complexity – though in relation to additional parameters, including (but not limited to) plant material, ripeness, extraction, use of lees, and use of new oak.
Bertelsen cites complexity and ageworthiness, specifically in wines that use lower amounts of SO2. In the context of Pinot Noir, Braiden Albrecht, winemaker at Mayacamas, agrees, stating that whole clusters can add body and tannin, specifically in cooler years.
"In vintages where Pinot will be a touch lighter in color and texture, whole cluster use is a great tool to provide structure and length," he says.
Additionally, Albrecht states that the potassium in the stems will also increase the wine’s pH, which can also be beneficial during cooler years.
On the contrary, he notes that poorly integrated whole clusters can add a strong stemmy/woody character to a wine, which can often be perceived as unpleasant. Similarly, Debeaulieu cites unwanted green herbaceousness, along with "the simple and narrow expression of a technique rather than wine at its best" as cons of an inharmonious whole cluster inclusion.
Mosbacher and Fischer state that in general, destemmed lots – due to their higher peak fermentation temps and no other non-grape material – produce wines that have more purity of fruit, less noticeable tannin, and more red-fruited flavors and aromas; whole clusters, on the other hand, produce wines with spicy or lightly pyrazine notes from the stems, and more pronounced tannin structure.
"Stems can be magical!" Mosbacher exclaims, highlighting the mouthfilling structure and "drying tannin without bitterness" that they can provide, along with spicy, clove and cinnamon-like notes when ripe (or on the other hand, green peppercorn and rosemary notes when less so). Stoumen echoes this, stating that whole clusters can bring a balancing savory element to riper fruit, which is particularly attractive in California grapes.
"The process of whole cluster fermentation is magical, too," Mosbacher reveals. "By preserving the whole structure of the grape cluster, you can ferment slower and cooler, achieving flavors and aromas not found in destemmed lots."
Though with anything, balance and judgement is key.
"Stems can be a disruptive variable in the expression of a wine, so it needs to be well judged," Debeaulieu says, affirming that their inclusion must be at the service of the fruit, and above all, expression of place.
