Breaking Down Grapes to Build a Better Wine

Photo Credit: Terlato Wines

It is a frequent statement in winemaking that grapes should be handled as delicately as possible, when they are being harvested, so that they get to the crush pad in a pristine condition, with only whole bunches and fully intact berries. Harvesting grapes by hand and carrying them to the winery in tiny boxes are almost universally praised as superior, yielding to better wines because fermentations will be healthier and aromatic development better. However, there are moments when your grapes will not thank you for being so nice.

Sometimes, you actually need to shake things up a bit more, so that the grapes can express themselves fully. Jamie Marfell, chief winemaker at Stoneleigh, a producer in Marlborough, New Zealand, points out that, in the case of sauvignon blanc, he actually likes a little rougher approach to harvesting. “Machine harvesting is important, in this case, and can have advantages.

“It’s actually positive for the grapes to get beaten up a bit. You get better aromas, because it releases more thiols.”

Precursors in the skins

In white aromatic varieties like sauvignon blanc (but also petit manseng, verdejo, petite arvine and others), breaking down the berries allows certain aromatic precursors to be extracted from the skins. More specifically, this is the case for PassionFruitthiol precursors like 3-mercapto-1-hexanol (3MH, for short), 3-mercaptohexyl acetate (3MHA), and 4-methyl-4-mercapto-2-pentanone (4MMP), which result in aromas like passion fruit, gooseberry and grapefruit (and also cassis in red wines from cabernet sauvignon, though that’s another story).

When they come in contact with the yeast, these precursors (which are actually odorless), will then be transformed into the above mentioned aroma compounds, contributing to the distinct, fruity varietal aromas that today’s consumers seem to enjoy so much.

Since these precursors are essentially located in the skins, breaking down the berries in some way or other will allow the compounds to come out in the resulting musts. Maceration on the skins or the use of a slow and relatively hard press cycle are also possible ways of ensuring the extraction of these compounds.

Even if you’re being tougher on the grapes, you should still be exerting care. Extensive contact between juice and skins can also mean that the resulting juice will contain more phenolics, potentially resulting in increased bitterness, darker color, and higher propensity for browning.  So why is it that winemakers are sometimes observing more intense thiol aromas and better wines when the grapes are not treated with kid gloves?

Letting the air in… at the right moment

One reason is that when grapes are not treated too gently, they are exposed to oxygen. And at this early stage, allowing oxygen to be in contact with the grapes and must is also a good way to promote a better presence of desirable aromatic contents.

When it comes to varietal thiols, having oxygen as an active part of the process may seem like a bit of a paradox. After all, preserving thiols generally requireGlutathiones protecting the wines from oxygen as much as possible. However, the key here is that the effects of having broken down the grapes is felt on aromatic precursors of thiols, and not on the thiols themselves. It has been long known that when the must is oxidized, leafy aroma compounds (also known as C6 compounds, as they contain six carbon atoms) are formed. Recent research has shown that one of them, namely 2-hexenal, can react with the natural grape antioxidant glutathione, to form more of these desirable thiol precursors. So more oxygen means more C6, which means more thiol precursors and, in the end, more aromatic thiols.

At that stage, freeing up the precursors puts more of them in the must, thereby providing more opportunity for the aromas to develop as vinification moves forward. As an added benefit, allowing oxygen contact at this stage can help remove phenolics, components that are highly reactive and could result in unwanted wine oxidation at later stages.

Once the right set of aromas have developed, it will be time to protect them and nurture them, so that all the lovely elements made available by proper ripening and healthy ferments remain in the wine for everyone to enjoy. Being tougher or gentler is all a question of timing.


About the Author

Rémy Charest is a Quebec City-based journalist, writer, and translator. He has been writing about wine and food since 1997 in various Canadian and American print and online publications, includijng Le Devoir, Le Soleil, Coup de Pouce, EnRoute, Palate Press, Punch Drink, WineAlign and Châtelaine, and has been a regular radio columnist for Montreal's CJAD and CBC/Radio-Canada. He is additionally a wine judge for national and international wine competitions, notably the National Wine Awards of Canada and the World Wine Awards of Canada organized by WineAlign.

Rémy Charest Photo Credit: Jason Dziver


  1. Well, this seems out of the usual line of thought. Everywhere you look, Sauvignon Blanc is the variety which is worked on the most reductively. Infact I think the kiwis use higher levels of SO2 and also introduce ascorbic acid during crushing to minimize oxygen pickup. They wouldn’t do the same for say a Chardonnay which is known to handle much more oxygen than other varieties. This is flying against all that….

    1. Indeed, it looks like there’s more than one way to skin a grape. I’m not sure it’s true that sauvignon blanc is worked the most reductively everywhere, though: think of the Loire or Bordeaux, with barrel-aged whites, for instance. And again, you have to keep in mind the difference between the thiol precursors and the thiols themselves.

Leave a Reply