Much red wine labelled Côtes du Rhône is produced using semi-carbonic maceration. Answer the following questions about the process. 

[Answer(s) based on WSET Level 3 material]

I’m going to back up a bit before I get to the actual questions. And talk about carbonic maceration (because I think it a bit odd to ask about semi, when the full story has yet to be told).

Carbonic maceration is a type of “whole bunch ferment.” The objective of this technique is to create an oxygen-free environment for the uncrushed fruit. That is an important thing to take note of, as the lack of oxygen a)forces berries to transfer sugars into alcohol inside their cells, without the involvement of yeast. This intracellular fermentation creates distinctive fruity aromas inside the berry which will contribute to the resulting wine’s flavor and aroma profile.

The process involves placing whole, uncrushed bunches of grapes into fermentation vats and then topping off the vat with CO2 which removes all oxygen. The removal of oxygen is what causes the intracellular fermentation to start. (For my fellow fitness geeks, let’s think about this as an anaerobic exercise.) So, the inside of the grape is turning sugar molecules into alcohol, but (like building a muscle) once it reaches a certain threshold (about 2% alcohol), the grape skins start to split, and the grapes will release juice. At this point, the winemaker will typically drain the juice from the skins and continue with a yeast-based fermentation process.

Why bother? This is a technique used to extract color from the grape skins without extracting tannin. Thus, resulting wines are soft, fruit forward, with distinct candy-like flavors. “Bon bon anglais,” as I heard one winemaker describe it. (Candy of the Englishman).

Right, so now that we have that covered, let’s answer the original question(s)…

What are the main considerations when selecting grapes for semi-carbonic maceration?

For semi-carbonic maceration, as with carbonic maceration (and whole cluster pressing for that matter), the grapes—as well as the stems‚ must be fully ripened. If not, those unripe stems will add some funky flavors to the wine during the maceration process. Another important note is that these grape clusters need to be picked by hand to a) ensure that those stems are at full ripeness, but also b) to ensure that those whole clusters, well, stay whole clusters. Typical machine harvesters collect grapes by shaking the vine, a process that will inevitable separate berries from stem. Some, more aggressive machinery, may even break grapes during the process (although technology is such that one can probably find gentler options if needed), which defeats the whole purpose of whole cluster inclusion.

Describe the process of semi-carbonic maceration.

Ok. So, this is similar to the above process except no CO2 is used. That means that there is oxygen left at the top of the enclosed tank during the process. So, what happens here is that the whole cluster once again is placed into the vat, the weight of the whole cluster berries on top squish the whole cluster berries on the bottom, which then release grape juice. There is oxygen in the tank, so ambient yeast will form and begin to ferment the released juices. A by-product of alcoholic fermentation is…you guessed it: CO2. Well, this is a closed fermentation vessel, there’s nowhere for that C02 to go. So, the trapped C02 forces those top berries, that are still completely in tact, to undergo the intracellular fermentation described above. Again, once those top berries begin to split, this is when the juice will be pressed off skins and fermentation off-skin will continue.

NOTE: There are some Pinot Noirs created with this technique but fermentation will continue on the skins. For this technique, the winemaker will conduct regular punchdowns over the course of a few days. This will slowly decrease the amount of carbonic maceration taking place until all grape material is broken up. Alcoholic fermentation will continue on the skins and some winemakers may even include a post-fermentation maceration to further integrate the flavors of the carbonic maceration process.

Under the headings below, describe the typical style of a newly released, inexpensive red Côtes du Rhône wine produced by semi-carbonic or carbonic maceration.

Ok, so, first a bit about Côtes du Rhône, a generic appellation found in the Southern Rhône. Côtes du Rhône accounts for more than half of the entire production of the Southern Rhône and, as you may have predicted or may have tasted, the wines are typically simple, medium bodied wines. This is different than the Côtes du Rhône Villages. To qualify for village status, there are more stringent minimum alcohol levels, maximum yields, and a greater percentage of the red blends must be made with Syrah, Grenache, and Mourvédre. (NOTE: There are a few villages that can put their name on the Côtes du Rhône Villages label if and only if 100% of the grapes are sourced from that named village. These guys are the créme de la créme outside of the wines that qualify for cru status [by the way, these guys can apply for crus status if they want] and have more body, structure, and spice-filled notes than the generic Côtes du Rhône, which I’m actually supposed to be talking about…)

Nose: The nose will have simple aromas of red fruits: red cherry, red currant, red plum, and that candy-like scent mentioned above as well.

Palate: These wines will be dry with low to medium tannin levels (remember carbonic extracts color, not tannin), and a medium-weighted body.

Conclusion: These wines are absolutely intended to be enjoyed young and are not suitable for extended aging.

I’m going to add a footnote here. These questions specifically asked about the Côtes du Rhône, but the hot spot for carbonic and semi-carbonic maceration has to be Beaujolais. Indeed, that Beaujolais Nouveau everyone was drinking a few weeks ago, as well as generic Beaujolais appellated wines are usually made with one of these two methods. Just…want to throw that out there. We’ll do a deep dive into Beaujolais soon, as well as the rest of the Rhône. Stay tuned…

Adding another note I came across during my (millionth) read-through of the text: Semi-carbonic maceration is a technique utilized in Rioja (the Uper Ebro in Spain) to produce wines intended for early drinking. Keep that in your back pocket…sounds like one of those little notes that may pop up as a multiple choice. 😉

And with that, I’ll turn it over to you! How’d I do? Anything you’d like to add about the carbonic or semi-carbonic maceration process? Any winemakers you know (or are you a winemaker) utilizing the process? How are those wines tasting?

And a quick thank you for all those who’ve been leaving comments either here or on Facebook. I’m also on Twitter (although getting all of those messages can be hard). Your comments, questions, and notes are all extremely helpful as I study up for this exam. So let’s keep the conversation going! Cheers 🙂

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2 Comments on Winemaking Pop Quiz: Carbonic Maceration

  1. How is unintended fermentation by wild yeast (or spoilage from bacteria) prevented while carbonic maceration is taking place? Is there a cleaning or sulfite addition prior?

    • The closed, inert vessel is being filled with CO2, which means there is no oxygen available. And thus, there cannot be any other fermentation taking place than the intercellular inside each grape, until the skins break. Then, there will be a more conventional fermentation, either on the skins or first pressed. This can be with ambient yeast or added yeast.

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