I found it at http://www.winewisdom.com/articles/techie/role-of-carbon-dioxide-in-still-wines/.
Hopefully it is acceptable forum protocol to cut/paste this type of information.
I am sharing the article to start a discussion about role of C02 post fermentation in Mead so that I can discover if degassing after primary is a good thing or no. I am familiar with the mead vs wine vs beer debate.
Would we consider a big dark fruit melomel a "red" wine?
For better and worse, carbon dioxide (CO2) is implicated in several aspects of still wine making and flavour profile. Apart from imparting a spritz to a still wine, are high levels of CO2 implicated in other issues of reductive winemaking? How does one separate the good from the bad, leaving the ugly purely as a matter of personal opinion?
Carbon dioxide (CO2) is produced by yeast as a natural product of fermentation. It’s great for keeping oxygen away from must and wine.
Received wisdom has it that CO2 becomes perceptible to the human palate at around 1g/l as a slight spritz on the tongue, akin to the sensation given by Muscadet sur lie. At around 2g/l wine is legally semi-sparkling (see below).
Its moderate presence helps to freshen a wine and gives a perception of slightly elevated acidity. “higher CO2 gives a crisper wine, with lower dissolved oxygen, less flavour intensity, and an addition to texture.” a bit of CO2 helps to preserve the wine a little, so you can lower sulphur dioxide (SO2) levels fractionally.
At too-elevated levels it makes the wine spritzy and can lead to reductive notes especially in reds. CO2 management activist, Abrie Bruwer, of Springfield Estate in South Africa, says “CO2 on the palate belittles a still wine. It makes the wine thinner and masks the nose. Think how difficult it is to assess the nose of sparkling wines.”
Julian Grubb, head winemaker of Chilean VIA Wines has winemaking objectives of “1000 – 1100 mg/l CO2 in aromatic whites, 800mg/l in and less than 500mg/l in reds. CO2 can make tannins sharper, more aggressive.
“Levels should be appropriate for the style of wine or organoleptically not apparent.
Reductive winemaking – winemaking which actively avoids oxygen – generally results in higher levels of CO2 in the wine, from retained fermentation-derived CO2 and from external sources of CO2 which have dissolved into the wine.
During fermentation, naturally produced CO2 protects the fermenting must from oxidation. After fermentation, a deliberate management policy must be adopted, depending on wine style.
Carefully controlled use of CO2 in the winery can optimise levels of oxygenation in the wine making process. Blanketed over the surface of wine, CO2 can help prevent oxidation and the growth of spoilage organisms. But it dissolves more readily in wine at the lower temperatures usually used by winemakers who work reductively. This makes it a potential problem for red wines, which need much less dissolved CO2. Additionally, as wine warms up, CO2 comes out of solution and pressure may build if there is no escape route.
“We use CO2 in bottles to work more reductively. We add it in the tanks, in trucks, during filtration etc., to remove oxygen. We also use a lot of dry ice. Its temperature is very low, so it is good for both cooling down grapes and keeping oxygen away;
Reh Kendermann are big exporters to the UK. Hofmann says: “we are looking for around 1 g/l CO2 in the wine for the bottling of whites and less than 500 mg/l for reds. Oxygen in the must destroys the pyrazines. Ascorbic acid scavenges very quickly, binding with SO2.
“We test CO2 before bottling and will blow off some if it is above 1400mg/l.
Harrop emphasises a style-specific approach to CO2. “Although some grape varieties e.g. riesling, sauvignon blanc, appear to support relatively high CO2 levels, a CO2 strategy should be predicated on wine style and vintage characteristics.”
On reds, Bruwer uses CO2 during the cold soak – it means volatile acidity takes a little longer to form. But during fermentation, Bruwer’s policy is to remove CO2: “we pump over with a fan blowing onto the cascade to give O2. Yeast under hot conditions produces glycerol if O2 is present. We want glycerol, rather than just alcohol, so we give O2.”
Taylor confirms that noticeable CO2 in still red wine is most likely indicative of a problem.
Noticeable CO2 could indicate a secondary fermentation, especially with the apparent trend to bottle some high volume reds with sufficient residual sugar to stimulate a refermentation.
Taylor says: “an increasing area is that of bottling red wine before it’s finished the malolactic fermentation. This can cause big problems. Not only do you get a slight spritz, but the bacterial damage can be significant. A heavy deposit is formed which might remain in suspension giving a cloudy wine. As the bacteria utilise the available SO2, oxidation occurs. There is much individual bottle variation. This is occurring right across the quality spectrum. Likely origins include the pressure to get wines to market earlier, or logistical pressure on tank space.”
Taylor sees this phenomenon on some very nice wines. The bacteria can remain viable in bottle for some time, 12 to 18 months; it takes maybe a combination of temperature and a drop in SO2 to a point where the bacteria can work.
Bailey warned of the potential impact of high CO2 levels for bag-in-box. “Above 600-800mg/l and the bag may swell when the temperature rises as CO2 comes out of solution. From the outside, it looks like a refermentation.”
Regarding screwcaps, Harrop suggests virtually no CO2 escapes, so a wine bottled at 1.2g/l stays that way, so with a noticeable spritz, but “with 1.2 or 1.1g/l at bottling under cork, after shipment a wine generally loses 100-150mg over 4-6 weeks, depending on the quality of closure, diameter of bottle, temperature etc., so there’s no over-spritz.”
The significance of the temperature of storage and logistics has been reported elsewhere – as wine heats, for example when containers move over the equator, CO2 comes out of solution and risks pushing out driven closures.
Active use of CO2 is both the friend and the enemy of reductive winemaking and needs to be critically monitored throughout the winemaking process to ensure optimum wine health.
When must and wine is treated reductively, it becomes especially vulnerable to oxidation, so every process after the first reductive process must be done reductively. CO2 use is an integral part of oxygen avoidance, as is cold temperature storage where CO2 retention is higher and risks include reductivity in the wine. If left unchecked, the risk is for reductivity to progress to irreversible mercaptan form.
With the trends to make more reductive styles, to minimise the time from harvest to market and to drink the youngest wines available, the use of potentially more reductive closure types has implications for the final wine analyses immediately prior to bottling. If “too” reductive a closure is used any present reductivity may persist and develop further. A bit more time after bottling or a “less” reductive closure may allow more opportunity for gases to equilibrate inside and outside the bottle.
A CO2 policy for still winemaking and bottling becomes increasingly relevant.
So my question is ................. for MEAD making is C02 relevant or is degassing the way to go?
Thanks
Steph
Hopefully it is acceptable forum protocol to cut/paste this type of information.
I am sharing the article to start a discussion about role of C02 post fermentation in Mead so that I can discover if degassing after primary is a good thing or no. I am familiar with the mead vs wine vs beer debate.
Would we consider a big dark fruit melomel a "red" wine?
For better and worse, carbon dioxide (CO2) is implicated in several aspects of still wine making and flavour profile. Apart from imparting a spritz to a still wine, are high levels of CO2 implicated in other issues of reductive winemaking? How does one separate the good from the bad, leaving the ugly purely as a matter of personal opinion?
Carbon dioxide (CO2) is produced by yeast as a natural product of fermentation. It’s great for keeping oxygen away from must and wine.
Received wisdom has it that CO2 becomes perceptible to the human palate at around 1g/l as a slight spritz on the tongue, akin to the sensation given by Muscadet sur lie. At around 2g/l wine is legally semi-sparkling (see below).
Its moderate presence helps to freshen a wine and gives a perception of slightly elevated acidity. “higher CO2 gives a crisper wine, with lower dissolved oxygen, less flavour intensity, and an addition to texture.” a bit of CO2 helps to preserve the wine a little, so you can lower sulphur dioxide (SO2) levels fractionally.
At too-elevated levels it makes the wine spritzy and can lead to reductive notes especially in reds. CO2 management activist, Abrie Bruwer, of Springfield Estate in South Africa, says “CO2 on the palate belittles a still wine. It makes the wine thinner and masks the nose. Think how difficult it is to assess the nose of sparkling wines.”
Julian Grubb, head winemaker of Chilean VIA Wines has winemaking objectives of “1000 – 1100 mg/l CO2 in aromatic whites, 800mg/l in and less than 500mg/l in reds. CO2 can make tannins sharper, more aggressive.
“Levels should be appropriate for the style of wine or organoleptically not apparent.
Reductive winemaking – winemaking which actively avoids oxygen – generally results in higher levels of CO2 in the wine, from retained fermentation-derived CO2 and from external sources of CO2 which have dissolved into the wine.
During fermentation, naturally produced CO2 protects the fermenting must from oxidation. After fermentation, a deliberate management policy must be adopted, depending on wine style.
Carefully controlled use of CO2 in the winery can optimise levels of oxygenation in the wine making process. Blanketed over the surface of wine, CO2 can help prevent oxidation and the growth of spoilage organisms. But it dissolves more readily in wine at the lower temperatures usually used by winemakers who work reductively. This makes it a potential problem for red wines, which need much less dissolved CO2. Additionally, as wine warms up, CO2 comes out of solution and pressure may build if there is no escape route.
“We use CO2 in bottles to work more reductively. We add it in the tanks, in trucks, during filtration etc., to remove oxygen. We also use a lot of dry ice. Its temperature is very low, so it is good for both cooling down grapes and keeping oxygen away;
Reh Kendermann are big exporters to the UK. Hofmann says: “we are looking for around 1 g/l CO2 in the wine for the bottling of whites and less than 500 mg/l for reds. Oxygen in the must destroys the pyrazines. Ascorbic acid scavenges very quickly, binding with SO2.
“We test CO2 before bottling and will blow off some if it is above 1400mg/l.
Harrop emphasises a style-specific approach to CO2. “Although some grape varieties e.g. riesling, sauvignon blanc, appear to support relatively high CO2 levels, a CO2 strategy should be predicated on wine style and vintage characteristics.”
On reds, Bruwer uses CO2 during the cold soak – it means volatile acidity takes a little longer to form. But during fermentation, Bruwer’s policy is to remove CO2: “we pump over with a fan blowing onto the cascade to give O2. Yeast under hot conditions produces glycerol if O2 is present. We want glycerol, rather than just alcohol, so we give O2.”
Taylor confirms that noticeable CO2 in still red wine is most likely indicative of a problem.
Noticeable CO2 could indicate a secondary fermentation, especially with the apparent trend to bottle some high volume reds with sufficient residual sugar to stimulate a refermentation.
Taylor says: “an increasing area is that of bottling red wine before it’s finished the malolactic fermentation. This can cause big problems. Not only do you get a slight spritz, but the bacterial damage can be significant. A heavy deposit is formed which might remain in suspension giving a cloudy wine. As the bacteria utilise the available SO2, oxidation occurs. There is much individual bottle variation. This is occurring right across the quality spectrum. Likely origins include the pressure to get wines to market earlier, or logistical pressure on tank space.”
Taylor sees this phenomenon on some very nice wines. The bacteria can remain viable in bottle for some time, 12 to 18 months; it takes maybe a combination of temperature and a drop in SO2 to a point where the bacteria can work.
Bailey warned of the potential impact of high CO2 levels for bag-in-box. “Above 600-800mg/l and the bag may swell when the temperature rises as CO2 comes out of solution. From the outside, it looks like a refermentation.”
Regarding screwcaps, Harrop suggests virtually no CO2 escapes, so a wine bottled at 1.2g/l stays that way, so with a noticeable spritz, but “with 1.2 or 1.1g/l at bottling under cork, after shipment a wine generally loses 100-150mg over 4-6 weeks, depending on the quality of closure, diameter of bottle, temperature etc., so there’s no over-spritz.”
The significance of the temperature of storage and logistics has been reported elsewhere – as wine heats, for example when containers move over the equator, CO2 comes out of solution and risks pushing out driven closures.
Active use of CO2 is both the friend and the enemy of reductive winemaking and needs to be critically monitored throughout the winemaking process to ensure optimum wine health.
When must and wine is treated reductively, it becomes especially vulnerable to oxidation, so every process after the first reductive process must be done reductively. CO2 use is an integral part of oxygen avoidance, as is cold temperature storage where CO2 retention is higher and risks include reductivity in the wine. If left unchecked, the risk is for reductivity to progress to irreversible mercaptan form.
With the trends to make more reductive styles, to minimise the time from harvest to market and to drink the youngest wines available, the use of potentially more reductive closure types has implications for the final wine analyses immediately prior to bottling. If “too” reductive a closure is used any present reductivity may persist and develop further. A bit more time after bottling or a “less” reductive closure may allow more opportunity for gases to equilibrate inside and outside the bottle.
A CO2 policy for still winemaking and bottling becomes increasingly relevant.
So my question is ................. for MEAD making is C02 relevant or is degassing the way to go?
Thanks
Steph
