Whither Co-fermentaton ?

There are many practical reasons to co-ferment that historically have weighted heavily in favor of doing so.

Historically perhaps the most frequent instance of co-fermentation of different grape varieties is when there is a field blend in the vineyard. These field blends are normally planted on fairly small plots and the existence of several grape varieties planted apparently at random seems very much a part of the terroir.  Even if one wanted to separate out the varieties it may not have been practical to do so. 

Although of course many field blends may have been planted out of sheer expedience or what was then available to be planted, there may of course be considered reasons why the field blend contains two or more varieties. One thinks of Cote Rotie for example , where a portion of Viognier may be included in the vineyard among the predominant Syrah. These white Viognier grapes are tossed into the vat together with the red grapes, because it is thought that their inclusion makes a positive contribution to the final wine - Viognier’s silky mouthfeel and expressive aromatics moderate some of Syrah’s more brutish tones.

There are, however, additional but less evident benefits to co-fermentation than simply blending the qualities that each individual grape variety contributes. For example, the presence of even small proportions of Viognier have been shown to stabilize the color of the Syrah. Ridge Vineyards have done analysis on this subject and conclude  -“ the theory is that viognier helps stabilize syrah’s color; the condensation reactions between viognier’s flavanols and syrah’s anthocyanins form highly stable polymerized molecules that stay with the wine for life. Once these polymers form, they don’t degrade through normal oxidation reactions.”  The inclusion of Viognier may also slightly change the color of the Syrah towards the bluer side of the color spectrum.  But regardless of how it is now justified through today’s better understanding of the chemistry involved, it has been the case for many decades that co-fermentation of these two grape varieties in the Northern Rhone was thought simply to produce better wine. Co-fermentation may also favorably impact aromatics of both varieties. So there are reasons to do it beyond simply convenience and what each grape varietal intrinsically contributes to the blend - and in the case of some classic combinations of grapes these reasons now seem to have scientific explanation. 

The presumption, however, is that one is harvesting these grapes at the same time - and therein lies a certain loss of control if the grape varieties do in fact ripen at different times.  In the case of field blends this loss of control is something one evidently sacrifices. 

More common has been the co-fermentation of various plots of the same grape variety. In times of old this would not even have been considered co-fermentation. Even today this is done for expedience based on the size of fermentation vats available. Available space is in practice a major constraining factor in many cellars. If you don’t have small vats that can allow for fermenting different plots separately, you have little option but to toss everything into the larger vats. This does not necessarily mean that you have to harvest all the plots at the precisely the same time. Grapes from an earlier picked plot can be undergoing fermentation in the large vessel for a few days before additional grapes are added from a different plot that was harvested later.  But there are limitations to this. You cannot wait too long. Quoting from Alan Manley’s M8 website, referring to Barolo - “As each vineyard matures and is harvested, the fruit is added to tanks with fruit already in fermentation. This is called a “continuous ferment” and has fallen out of general use, but is consistent with older, traditional winemaking practices in this region”. Yet Alan, in composing is Barolo blend, has of late had to vinify his Monforte fruit separately, since this can ripen fully two weeks after the fruit from his newly acquired other vineyards, which prohibits co-fermentation of everything together in the continuous ferment manner, however much that may be desired. So even if one co-ferments when one can, there are practical limits. 

Beyond tolerances of a few days, co-fermentation results in loss of control as to optimal picking dates and of course any thought of holding back - and omitting from the blend entirely - any parcel whose grapes perhaps underperformed that year.  

Given the increased financial resources of winemakers who make wines from regions that now command high prices, the trend has been to equip cellars to allow for separate fermentation of many different plots in the larger vineyard holdings by having not just many fermentation vats but having them in many sizes, so they can operate optimally (by reason of their particular shape) on the quantity of grapes harvested from any particular plot. One has only to visit the cellar at Cheval Blanc in St Emilion to see the lengths to which this is now the mantra. Having precise control over harvest date and the ability to decide whether to include or exclude wine from any particular parcel in the final blend is today highly valued. A very great deal of money has been spent equipping modern cellars to have this capability, reflecting the heightened view of picking dates as one of the most important influences on wine quality.

Co-fermentation does of course preclude eliminating any parcels later.  For those who do not wish to eliminate parcels, co-fermentation is fine if the harvest dates allow for it. Maria Teresa Mascarello, at Cantina Mascarello in Barolo, for example, as I understand it will co-ferment wine from their four or five different vineyards because they take the view that the final wine requires the inclusion of all of these without exception and the harvest dates are close enough to allow for co-fermentation.  The final blend is made up of what nature gives them in yield from each parcel. Others, as a matter of doctrine, will vinify parcels separately and still elect never to eliminate any parcel from the final blend on the basis that the terroir sought to be reflected in the bottle includes all the parcels. Thus no parcel should be eliminated. Domaine Chave take this approach, though in their case not the full amount of each parcel is necessarily included in the final wine. But each parcel will be present to some degree. But parcels are vinified separately to allow for optimal picking dates / elevage in the hope of improving the quality of wine from each distinct parcel before blending. Others vinify separately and then will eliminate sub par parcels entirely. This is particularly common where the estate has a second wine and there are dozens of separately vinified parcels.  All these separate vinifications, driven out of a desire to control picking dates and subsequent elevage precisely, make the art of blending an increasingly relevant skill. But it also comes at whatever is the cost of not co-fermenting.

The picture is of Viognier and Syrah grapes ready for co-fermentation