Vine to Wine: Re-Embracing the Stem

Vine to Wine is a column focused on winemaking and viticulture around the world. Our latest contributor is Romain Bocchio, a viticulturist and winemaker with the international wine consultancy Derenoncourt Vignerons Consultants, which is  headquartered in Bordeaux. He has degrees in winemaking and literature and collaborates as a consultant for diverse wine estates in Bordeaux, Italy, and throughout the Mediterranean basin.

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Bordeaux has always been a place that knows how to look forward. Long before climate change and shifting consumer tastes shook up the wine world, winemakers here were already rethinking how wine gets made. In just the past 20 years – the blink of an eye in vineyard time – everything from how grapes are grown to how they’re aged has been retooled, often with stunning results. But sometimes progress comes with a blind spot.

For years, Bordeaux chased ripeness like a holy grail. This was especially true for merlot, the region’s most planted red grape. Getting rid of anything green – leaves, stems, anything that might scream “underripe” – became standard. Sophisticated machines were brought in to sort the harvest with ever greater precision, ensuring that only the purest, most mature fruit made it into the tank. In this world, the grape stem was the enemy.

Now, that may be changing. As warmer seasons push grapes to ripen faster, often by early September, the very techniques once considered cutting edge are showing their limits. To get full phenolic maturity – the kind that gives wine depth, not just sugar – winemakers sometimes have to pick later, sacrificing freshness and aroma along the way. Other times, waiting too long means losing the magic altogether.

In this uncertain landscape, some of us began to wonder if what we had tossed aside might be part of the answer. Could the stem, that scrappy bit of vine once considered a flaw, actually help?

Over six years, the team at Derenoncourt Vignerons Consultants put the idea to the test, working in real cellars and conducting rigorous comparative trials to observe the impact of stem use (or non-use) during fermentation.

What we found surprised us. Used wisely, the stem can do more than just carry grapes – it can bring nuance, structure and even a subtle sense of sweetness to a wine. Far from being a relic of rustic winemaking, it turns out to be one of the most sophisticated tools a winemaker has.

Of course, not all stems are created equal. Just like grapes, they vary from one variety to the next, from one year to another. And the color isn’t a reliable guide – some stems brown from sun exposure, while others stay green even when fully ripe. Pinot noir and syrah, for example, often go into fermentation with green stems and make beautiful wines.

To better understand what stems actually do, we also steeped them – much like tea – in hydroalcoholic baths, extracting their compounds and aromas. We studied the composition of the grape stems in the laboratory, as well as the accumulation dynamics of the desired aromatic compounds. At the same time, we carried out winemaking trials focused on the stems prior to fermentation and on the wines after vinification.

To characterize the specific aromatic profile derived from the stems themselves, we prepared stem-infused solutions at 12 percent alcohol by volume in order to specifically identify their influence. A perfumer helped us describe what we found, for example lemon peel, dried fruit, floral notes, hints of spice and forest floor. Yes, there were often some vegetal touches too, but they were faint, almost whisper-like.

Chemically, stems contribute three major types of aromas: grassy notes from so-called C6 compounds, cool camphor and pepper notes from salicylates, and trace amounts of terpene – the same compounds that give many flowers and herbs their scent.

Beyond aroma, stems change how a wine feels. They can slightly lower the alcohol or, more important, soften its burn. They release potassium, which may raise pH levels, but paradoxically, the resulting wines taste fresher.

Bringing Finesse

Structurally, stems add tannins – but with finesse. In lean vintages, they can add needed grip. In hot, dry years when grape tannins may be coarse or underdeveloped, stems can bring balance. They also contain astilbin, a phenol found especially in merlot, which adds a sense of sweetness – not sugar exactly, but roundness, fullness, polish.

It’s important to separate these effects from those of whole-cluster fermentation, which has its own set of aromatic fireworks. We chose to isolate the impact of the stem itself, but the possibilities of combining the two techniques are thrilling.

Yet, from an aromatic standpoint, it’s important to distinguish between the aromas derived from the stems themselves, and those resulting from the use of whole bunches. The whole bunches introduce a semi-carbonic maceration, often at low temperatures, which generates intensely fruity primary aromas.

It is true to say that when using whole clusters, the result is a kind of aromatic synergy , a true explosion of scent. The process combines the bright, fresh aromas of intracellular fermentation with those imparted by the stems alone.

Traditional whole-cluster vinification typically involves placing a layer of whole bunches in the middle of the fermentation tank. The quantity of whole bunch is evaluated as a percentage of the total mass, and varies depending on grape varieties and oenological objectives. The resulting physical, chemical and fermentative interactions can be compelling aromatically, though technically more difficult to control.

We made a key distinction between these two winemaking approaches: the use of whole clusters versus the addition of stems alone.

To focus our study on the latter, we opted for the second method : reintegrating a partial quantity of stems separated from their fruits into the fermentation tanks, thereby isolating their specific contribution from that of whole-cluster fermentation. This allowed us to fully understand the impact of the stems themselves, their specificity from one terroir to another and the exciting possibilities their use could offer.

For many, this runs counter to decades of dogma. Huge investments have been made in destemming equipment, all in service of wines that are clean, ripe, and modern. But maybe the stem deserves a second look – not as a return to rusticity, but as a way forward.

Used thoughtfully, the stem can help define a wine’s identity without overpowering its sense of place. It brings aromatic complexity, structural tension and even a touch of sweetness. That’s a rare combination, especially from something we used to throw away.

Sometimes progress means embracing what we once ignored. And sometimes nature gives us exactly what we need – right there, between the grapes.

– Romain Bocchio