Co-fermentation, why and what

Someone asked me recently what I thought about co-fermentation. The practice of fermenting different grape varieties together. This is different than most blends, which are created after the individual wines have been made.

The short answer, is that co-fermentation is harder to do, and much easier to do badly. So why would anyone want to take the risk? As my mentor Bucky Fuller said "the whole is greater than the sum of its parts."

By fermenting the grapes together, you can potentially end up with a wine that transcends what you can create by blending. On the other hand, it is much harder to make any adjustments, or hide any flaws, after the fact. Even if you reserve some of the grapes to vinify separately, you still may not be able to undo, or hide, anything that goes wrong in the co-fermentation process.

Part of the problems stems from the simple fact that different grape varieties have different fermentation needs. The time needed for maceration, the temperature controls, even the choices of yeast are all varietal dependent.

So again, why take the risk?

Some blends have both black and white grapes (e.g. Syrah with Viognier, a common blend in the Rhone and the elsewhere). When you make a red wine, you carefully check the how the color is doing throughout the maceration period. After a certain point, you can get no more color from the pomace into the wine. The red wine is saturated with color.

If you were to now take that same, supposedly spent pomace, and add it to a tank of fermenting white wine, you would indeed leach even more color from the pomace. It seems that wine is saturated with coloring agents (anthocyanins) long before the must is no longer capable of releasing them.

This is important to co-fermentation advocates. By fermenting white and black grapes together you introduce the process of copigmentation. Meaning that the juice from the white grapes are colored at the same time, and more or less the same rate, as the black grapes.

Compare this to adding white wine to red wine. More than a tiny amount of white wine, and you have lightened the color. By co-fermenting you end up with a wine that has a greater presence of white wine characteristics, but with all of the color of a red wine fermented by itself.

This commingling may well work with flavor components as well.

Many wines owe their complexity to their blend. Just as with cooking, adding ingredients together (in this case other types of wine) can result in complexity, with each flavor adding a new facet to the whole.

Again using the cooking analogy, if the flavors are allowed to "stew" together for a time, you end up with an entirely new set of flavors, none of which were possible just by adding the ingredients together in their raw state.

So co-fermentation is in essence a way to "stew" the flavors of the various grape varieties together. Blending gives you a nice complexity due to the separate, but harmonious flavors. Co-fermentation gives a completely different complexity and flavor structure, that can not be duplicated by blending alone.

It is a whole lot less dangerous, and therefore cheaper in the long run, to blend after the fact. It is a whole lot cheaper up front to co-ferment (since you do not need as many tanks and barrels, and can pick all of your grapes at once). Therefore one can not use economics alone to help you to decide on blending vs. co-fermentation.

It is just one of the many choices a winemaker has to decide about, long before the grapes arrive at her crusher.

It is not common for a wine to mention if it was co-fermented as opposed to blended, and so it is not often something the consumer can look for on the label. It is however a great question to ask the winemaker the next time you are visiting a winery. Does she co-ferment, and why?

Have a favorite co-fermented wine? Let us know about it. If there are any winemakers that would like to chime in on this subject, i certainly would love to hear their opinions.