Carbonic maceration: Art Nouveau

Today, the third Thursday in November, marks the launch of the 2010 Beaujolais Nouveau vintage. Young, light and fruity wines are often made with a special process called carbonic maceration, which leads to some of their characteristic aromas and flavors. Editor-in-chief Erika Szymanski explains this “yeast-free fermentation” process.

Carbonic maceration? Of course, I know what it is. I can tell you that it is commonly used for Beaujolais, leads to fresh and fruity red wines, and involves the fermentation of whole grapes. I thought I had a reasonable understanding of the concept. When the winegrowers say: “… and we had a carbonic maceration with the tempranillo this year…”, I nod and smile with as much serenity as when they say “malolactic” or “sur lie”. I wasn’t afraid to choose it as my experimental red wine variable in the lab I’m taking this fall.

Then, on a Thursday evening in October, I returned from our outing on the grape harvest site, impatiently awaiting a Merlot processing Friday. Anticipating an easy afternoon spent emptying whole bunches into vats, I thought about doing a little further reading on carbonic maceration (CM). All I expected was a few tips to impress our teacher and set our wine apart from the rest.

In about ten minutes, the scales fell from my eyes. I had blithely tossed “carbonic maceration” into conversations for years while remaining almost completely unaware of its implications. And what could they be?

According to Jancis Robinson in The Oxford Wine Companion, “Carbonic maceration is a red wine-making process that transforms a small amount of sugar from unground grapes into ethanol, without the intervention of yeasts. It is generally used to produce light fruity red wines with bright colors and fruit for early consumption, most famous but by no means exclusively in the Beaujolais region of France.

In Wine chemistry conceptsYair Margalit calls CM “a special type of fermentation that uses the ability of enzymes naturally present in grapes to turn a small amount of sugar into ethanol.” The process is eventually stopped by the build-up of alcohol which poisons the berry cells at about 2% ethanol.

Typically, carbonic maceration occurs in an oxygen-free environment, provided by the gassing of the grapes with CO2 in a closed tank. Some of the otherwise whole grapes will be crushed by the weight of the grapes above, and some winemakers make a point of leaving the grapes attached to the stems in whole bunches. Some winegrowers, after a period (1-2 weeks) of CM, squeeze the juice and allow traditional fermentation without the skins.

In terms of practical winemaking, removing the grapes from the stems inevitably involves some degree of crushing – just imagine the act of plucking the grapes from the stems on a large scale – and any vat is large enough that the grapes at the bottom are crushed. by the weight of the grapes at the top. The experimental merlot and our little winemaking lab were a whole different matter. Our CM ferments are made entirely from whole berries – even the grapes at the bottom – and maybe only 50% stick to the stems. I doubt, however, that you’ll ever see a pair of commercial winemakers (or cellar rats) spending three hours carefully stuffing whole bunches of Merlot grapes into two 5-gallon glass carboys on a Friday afternoon.

Why bother with CM?

Carbonic maceration is usually reserved for red and non-white wines. Consider that for white wines, skin contact is usually minimal, while CM naturally involves prolonged, if gentle, contact with the skin juice. Interestingly, however, up to 15% of a tempranillo can contain white grapes – usually viura – and it looks like the white bunches are co-fermented with the red grapes in this “soft” version of CM.

Beaujolais Nouveau being the best example, the only destiny of a CM wine is to be drunk young. These are party wines – some say spicy grape juice – with distinctive flavors that remind party goers of everything from raspberries to chewing gum, to grandma-scented bananas. Whether we like it or hate it, the contributions of CM are revealed in tannins, aromatics and acids.

Tannins: Tannins are found mainly in grape skins, and different tannins are found in different layers of the skin. Winemaking techniques that physically tear the skins extract more tannins from the skins and tend to make wines harder than soft techniques that leave the skins intact. Tearing the skin of red grapes therefore results in harder tannins (this is a major motivating factor that motivates wineries designed around gravity flow rather than mechanical pump transfers, pumping over versus pumping over. and other gentle techniques. intended to release the juice without pulverizing the skins. If fermentation begins inside a whole grape:

  • Less total tannin will be transferred from the skin to the juice contained inside the grape per unit of time. On the other hand, CM generally allows a longer total contact time between the juice and the skin. Since the way the tannins are transferred is different, the type and feel of the tannins should also be different.
  • Tannins present in the inner layers of the grape skin will preferentially migrate to the interior of the fermenting grape, while minimal tannins will be extracted from the outer layers of the skin.
  • The color of the wine will be less intense, that is to say, lighter. Anthocyanins, a group of pigments that give red wines their color, are concentrated in the skins. Open up a red grape and you can easily see that the skin is red while the internal flesh of the grape is a pale non-color. During CM, the type of anthocyanins that migrate into the internal parts of the grape or are released into the wine at the end of the fermentation of whole berries are qualitatively different from those released during the classic fermentation of red wines on the grapes. skins. This different anthocyanin profile gives CM wines an overall less intense color and a distinctive tint. (For more on this topic, see some fascinating recent and older work.)

In other words, a CM wine will be clearer in color and body than its standard processing counterparts.

Aromatics: That unrivaled floral-raspberry-barber shop aroma of CM wines is linked to higher levels of volatile substances like vinylbenzene, benzaldehyde, ethyl cinnamate, and ethyl phenylacetate, to name a few -a. Monoterpenes, a class of hydrocarbons related to the floral and fruity aromas of grapes (and other fruits), are also important. A higher overall concentration of monoterpenes in CM wines also helps explain their “fresh and fruity” nose.

Acid: As sugars are fermented into alcohol, grape enzymes also ferment malic acid – up to 50% of the total concentration – into alcohol. Malic acid, a strong tasting acid found in high concentrations in grapes, is converted to lactic acid by bacteria during the slow malolactic fermentation process in most red wines. This “malo-alcoholic fermentation” means that CM wines can forgo malolactic fermentation (avoiding the sweet and buttery lactic flavors while decreasing the lively Malic flavors) and maintain the perception of high acidity with lower actual acidity. . It also saves precious time, allowing Beaujolais Nouveau 2010 to be released on the third Thursday in November, while the 2010 reds with conventional fermentation will not make their debut for several months.

Start looking, and CM appears much more common than the classic Beaujolais example. In La Rioja (particularly in the Alavesa sub-region), Spanish winegrowers use CM to promote more fruity flavors in Tempranillo wines intended for blending. New world winegrowers from California to Australia who make “New” style wines have taken up the technique of gamay and other grape varieties.

And what about those 5 gallon carboys filled with whole Merlot grapes and topped with gasoline? After ten days of “chillin ‘in the winery” (as my lab mates constantly remarked) the grapes looked as fresh as the day they were picked. Even if it seemed that nothing was happening, these cold grapes were metabolizing very quietly: the wine we pressed that day entered its vat with 2.5% alcohol, a fruity nose and a very pretty deep fuchsia shade. The second cylinder, condemned to a full month of CM treatment, must be postponed tomorrow. These grapes look a little tired – metabolizing for 30 days in a row must be hard work! – but they are still intact. For the smell, the color and the alcohol level, I’ll keep you posted.

Erika Szymanski was fortunate to have parents who taught her that wine was part of a good meal, who thought well-behaved children belonged to tasting rooms with their parents, and who had too many books. Avoiding a midlife crisis in advance, she recently returned to her native Pacific Northwest to complete a doctorate in microbial enology at Washington State University. His goal, in addition to having goats one day, is to combine cellar work with research on how to improve the success rate of spontaneous ferments. When taking care of his Brettanomyces gives him enough time, his blog Wine-o-scope keep notes on why being a wine geek is fun.

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