Carbonic Maceration - chemistry help needed

[Lucienne]

There really should be a more generic science tag.

Anyway, studying for my wine exam I can't seem to understand the process of Carbonic Maceration.

Basically what you do is you place whole bunches of grapes in vats filled with CO2 and they start to ferment. My book says this is due to the fact the glucose in grapes doesn't have any oxygen to react with so in order to produce energy it converts the glucose to alcohol.

I do know the steps of the process, but the whole thing just doesn't make sense to me. I don't even understand why the grapes want energy in the first place.

As chemistry makes absolutely no sense to me what so ever, I'd really appreciate if a anyone could explain the science behind the process for me.

[Tyche]

I could be completely wrong, but the energy would be used by the yeast and not the grapes right?

[Churchill]

Editing first sentence, fermentation =/= alcohol metabolizing/oxidation lol.

Fermentation causes (food) to convert carbohydrates into alcohol.

When studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that the fermentation was catalyzed by a vital force, called "ferments," within the yeast cells. The "ferments" were thought to function only within living organisms. "Alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells,"[7] he wrote.
Nevertheless, it was known that yeast extracts ferment sugar even in the absence of living yeast cells. While studying this process in 1897, Eduard Buchner of Humboldt University of Berlin, Germany, found that sugar was fermented even when there were no living yeast cells in the mixture,[8] by a yeast secretion that he termed zymase.[9] In 1907 he received the Nobel Prize in Chemistry for his research and discovery of "cell-free fermentation."
One year prior, in 1906, ethanol fermentation studies led to the early discovery of NAD+.[10]

Wiki. His quote was really good, maybe it will help: "I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development and multiplication of cells..."

[Enygma55]

The Large Hadron Collider thread has kinda become the general Science thread. As for your question, no clue.

http://www.bluegartr.com/threads/775...adron-Collider

[Tyche]

It's pretty similar to metabolism in the body, humans convert glucose to pyruvic acid, which is then turned into lactic acid in anaerobic conditions (lacking oxygen). Lactic acid buildup is what makes you feel like trash when you excercise. In alcohol fermentation, alcohol is formed from the pyruvic acid. Glucose isn't converted straight to alcohol, there's a process it undergoes, and the lack of oxygen in the metabolism is what creates the alcohol. If oxygen was present, it would undergo Krebs and Electron transport most likely.

[Churchill]

It's similar but a somewhat reverse cycle and not following the same reasoning for occurring, that's why I edited it.

Fermentation also creates lactic acid just the more you know.jpg

[Tyche]

My bad, I guess poor wording on my part, alcohol metabolism, not fermentation. The extent of my chem is organic, but I did a hell of a lot of human A&P, the process looked familiar. I don't know a damn thing about alcohol, I don't even drink it.

[Lucienne]

Editing first sentence, fermentation =/= alcohol metabolizing/oxidation lol.

Fermentation causes (food) to convert carbohydrates into alcohol.



Wiki. His quote was really good, maybe it will help: "I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development and multiplication of cells..."

Not the same thing. You let the grapes go through the maceration before you add yeasts.

Carbonic maceration is a winemaking technique, often associated with the French wine region of Beaujolais, in which whole grapes are fermented in a carbon dioxide rich environment prior to crushing. Conventional alcoholic fermentation involves crushing the grapes to free the juice and pulp from the skin with yeasts serving to convert sugar into ethanol. Carbonic maceration ferments most of the juice while it is still inside the grape, although grapes at the bottom of the vessel are crushed by gravity and undergo conventional fermentation.

I too can use wikipedia.
I want to understand the process going on in the grapes, if you want to call it alcohol metabolizing that's cool with me, as long as you can explain to me why it takes place in words I can understand. Explain, not tell me it converts this shit to another, I can read, but grapes exploding by themselves make little sense to me. I understand traditional fermentation and malolactic fermentation reasonably enough.

[Lucienne]

It's pretty similar to metabolism in the body, humans convert glucose to pyruvic acid, which is then turned into lactic acid in anaerobic conditions (lacking oxygen). Lactic acid buildup is what makes you feel like trash when you excercise. In alcohol fermentation, alcohol is formed from the pyruvic acid. Glucose isn't converted straight to alcohol, there's a process it undergoes, and the lack of oxygen in the metabolism is what creates the alcohol. If oxygen was present, it would undergo Krebs and Electron transport most likely.

If you let wine ferment in oak, it will have access to small amounts of oxygen, it actually is one of the things you do to make wine that will age well.

[Churchill]

You mistook what we were saying and decided to go snooky on us, however, Carbonic Maceration is the same thing as fermentation. The difference between other methods and this is yeast is added as a catalyst after grapes have been crushed in a semi-oxygen free environment where as Carbonic Maceration forces grapes to undergo fermentation in a completely oxygen free environment without any added catalyst. CO2 says wassup to grape, grape says guess it's time to start tickling some cells.

[Lucienne]

You mistook what we were saying and decided to go snooky on us, however, Carbonic Maceration is the same thing as fermentation. The difference between other methods and this is yeast is added as a catalyst after grapes have been crushed in a semi-oxygen free environment where as Carbonic Maceration forces grapes to undergo fermentation in a completely oxygen free environment without any added catalyst. CO2 says wassup to grape, grape says guess it's time to start tickling some cells.

Not snooky, I just woke up, and this is how I generally sound.
Ok, so the CO2 basically causes the grapes to start the reaction? But why?

[Churchill]

There is bacteria on the grapes naturally, lack of oxygen creates an anaerobic environment and triggers the cells to react - cells react, produce ethanol and CO2, CO2 pushes out additional oxygen from chamber and causes more reactions.

It's the same thing that happens under anaerobic conditions in your body except your body creates lactic acid. Difference between regular wine and this is this method forces the grapes to undergo this process inside the grape, grape explodes naturally and the grapes at the bottom (apparently) undergo regular fermentation because there is almost no way for them to get the chemicals they need to react.

[Lucienne]

Why would the anaerobic environment cause a reaction. This is very confusing. You can seal wine with CO2 and preserve it for a while, so why does it all of a sudden trigger reactions?

I guess the grapes explode for the same reason a bottle of coke will foam when opened?

[Tyche]

If you're putting them in a huge vat, it's probably gravity crushing them.

[Lucienne]

Gravity crushes the ones furthest down, those ferment normally, the ones on top explode from the CO2 as far as I understand it.

[Talus]

It sounds more like a physics question than a chemistry question IMO.

Carbon dioxide is a very small, polar molecule so it moves about by simple diffusion through the grape's skin, similar to how it moves between tissues and capillary beds in our bodies. I'd guess the grapes become saturated with it, and the partial pressure of the CO2 moving into the grapes, added with the partial pressure of the O2 present in the grapes (and not in the vats) exceeds the pressure of CO2 outside of the grapes in the vats and the grapes burst to reach equilibrium.

[Edit: by adding the CO2, you're essentially driving the fermentation process within the grapes to get those "young wines" that Wikipedia talks about... quicker to market, I guess.]

[Edit 2: it reminds me of every A&P textbook and lab manual showing pictures of RBCs in hypotonic, hypertonic and isotonic saline solutions.]

[Lucienne]

It sounds more like a physics question than a chemistry question IMO.

It might very well be, the only science I really enjoy is math.

Carbon dioxide is a very small, polar molecule so it moves about by simple diffusion through the grape's skin, similar to how it moves between tissues and capillary beds in our bodies. I'd guess the grapes become saturated with it, and the partial pressure of the CO2 moving into the grapes, added with the partial pressure of the O2 present in the grapes (and not in the vats) exceeds the pressure of CO2 outside of the grapes in the vats and the grapes burst to reach equilibrium.

That was really interesting! Ok, so basically the CO2 will penetrate the grapes and bring inside the bacteria that's on the skins, which will trigger the fermentation or something like that?

[Edit: by adding the CO2, you're essentially driving the fermentation process within the grapes to get those "young wines" that Wikipedia talks about... quicker to market, I guess.]

When you ferment red wine traditionally, the contact with skins will make it more or less tannic, you know how when you drink red wine it can give you a dry, sticky feel in your mouth, that's to great extent avoided by the carbonic maceration, and at the same time you get out a lot of fruity flavors. You still have to ferment the wine after the maceration, because there will be lot of sugar left in the grapes. What they mean with young wines is wines that aren't intended for aging. Generally you need a lot of structure and complexity for it to develop with years.

[Edit 2: it reminds me of every A&P textbook and lab manual showing pictures of RBCs in hypotonic, hypertonic and isotonic saline solutions.]

I have no idea what this is.

[Chun Liroy]

Ok so, this is the way I see it.
Yeast is present in grapes naturally in small amounts. This is called ambient yeast. In traditional wine making, cultured yeast is added to the smashed grapes, and fermentation occurs. Think of fermentation less as a process of the grapes, and more of as a process of the yeast. The grapes supply the fuel (some nutrients--others are added by the winemaker-- sugar) for the yeast to create ethanol. I'm not too keen on a yeast's life cycle but i'm sure they have two pathways for energy production: Aerobic and Anaerobic. The CO2 in the wine barrel is used as a filler to the barrel to create an anaerobic environment. I *think* that CO2 is used because it is a natural by-product of the production of energy for the yeast. Like Tyche said, glucose is broken down into multiple atoms of acetaldehyde, which is then used in either anaerobic or aerobic reactions depending on the current environmental conditions. The byproduct of the reactions breaking down the glucose is CO2, thus using CO2 as a filler ensure no additional reactions take place, altering the taste of the wine in some way(?). The yeast, like humans, would like to go into its aerobic cycle for energy, but since there is no O2, the anaerobic processes take place.

In Carbonic Maceration, it seems that instead of creating a must and adding yeast to it, the grapes are allowed to ferment naturally with the ambient yeasts they contain, this is propelled by the pumping of CO2 into the container, creating an anaerobic condition within the grapes due to diffusion. I'm not sure on the exact cause (I can look it up...) of the bursting, but maybe has something to do with the build up of various compounds due to fermentation.

As far as fermentation not occuring when they add CO2 to carbonate the wine, it happens because the yeast has finished its life cycle and so there is no more fermentation taking place. The yeast dies, and sinks to the bottom and the top of what they take from, afaik.

Hope this helps.

[Lucienne]

Like Tyche said, glucose is broken down into multiple atoms of acetaldehyde, which is then used in either anaerobic or aerobic reactions depending on the current environmental conditions. The byproduct of the reactions breaking down the glucose is CO2, thus using CO2 as a filler ensure no additional reactions take place, altering the taste of the wine in some way(?). The yeast, like humans, would like to go into its aerobic cycle for energy, but since there is no O2, the anaerobic processes take place.

You lost me here. The first part was very informative and simple enough.

I think the grape might burst because it gets overfilled with the stuff it starts producing, it would make sense.

The wine will still react with oxygen though, but then that's oxidation.

You guys are great btw!

[Chun Liroy]

Yeah, that part was probably unclear. In humans, a 6 carbon sugar (glucose? idk i forget) is broken down into 2 pyruvate molecule. This happens regardless of conditions. The pyruvate then will go into the krebs cycle and ETC, but only if oxygen is present. If there is not oxygen present, then it goes into the lactic acid formation. The same thing happens in the yeasts, except replace pyruvate with acetaldehyde (and of course lactic acid with fermentation).

The byproduct of creating the acetadehyde is CO2. You were asking about why the CO2 causes fermentation to occur, but it's not so much the presence of CO2 as it is the lack of O2. I'm guessing that the CO2 from the natural process is either:
A) not effecting the taste/smell of the wine, or
B) The altering of the taste/smell due to it is unavoidable.

Since either of those occur, the CO2 is then used as a "filler" (since I don't think it is practical to create a vacuum for wine making). If other gases are used, those could react with the fermentation products, altering the taste or smell (again, I have no idea, I'm merely taking an educated guess). That's basically what I was trying to say, lol.

Hope it's clearer, my mind does not work in a traditional sense when forming ideas. :<