from La micro-ogxygenation ou micrbullage, wine-note.com”

 

Uptake of oxygen during normal winemaking operations

There are several steps during the winemaking process when oxygen is introduced into juice and wine. Oxygen is introduced almost every time the wine is moved and even during storage (Table 1). After introduction to the wine, oxygen is quickly bound by various components of the wine including ethanol (to form acetaldehyde), phenolics (tannins and anthocyanins), SO₂, aroma and flavor compounds, and can have a profound effect on astringency and aroma. When a red wine (at 20°C) is saturated with oxygen, it contains an average of 6.3 -8.4 mg/L.^1,2 Due to oxygen binding with other compounds in the wine , this level reduced to only 1 mg/L within 6 days³. During the course of red winemaking at least 10 saturations are beneficial for the evolution of the wine, while most red wines can tolerate at least 30 saturations, depending on their phenolic content². 

Table 1: Oxygen introduction during winemaking operations^1,3

Unlike the uncontrolled addition of oxygen during cellar operations, micro-oxygenation (MOX) is the process of intentionally adding small amounts of oxygen in a measured way to induce favorable changes in color, aroma, and texture⁴. The technique was first developed in France in the 1990’s as a way of aging of tannic red wines in stainless steel tanks rather than oak barrels. It is now also used to accelerate aging, stabilize color, and treat reduction and herbaceous/green character. Rather than shortening the life of a wine, as oxidation normally does, MOX  can increase the anti-oxidative power and potential aging of the wine by stimulating phenolic reactivity¹.

Chemical and Sensory effects of micro-oxygenation

When oxygen is introduced to wine, it diffuses randomly and encounters many chemical compounds in the wine. Oxygen is generally highly reactive and will show the most effects in those chemicals that are found in the highest concentration in wine, such as ethanol, anthocyanins, tannin subunits, and tannins themselves. Oxygen will also interact with molecules that are responsible for aroma and flavor. Though a winemaker may be targeting one component, oxygen will interact with them all.

One of the most common reasons to micro-oxygenate wine is to help structure tannins. Phenolics such as anthocyanins and tannins are responsible for the color and mouthfeel (astringency) of red wine. The full chemistry of oxygen and phenolics in wine is complex and beyond the scope of this newsletter, however, a few details might aid in understanding the effect of MOX on astringency and color stability. 

Tannins themselves are polymers, large molecules composed of smaller subunits that are bonded together in a specific way. After tannin polymers are extracted from the skins and seeds of grapes, acid hydrolysis in the grape juice and wine breaks these large polymers into smaller polymers and monomers. Phenolic monomers can exist in different oxidation states at wine pH, some of which are more reactive than others. The phenolic compounds extracted from grape skins and seeds are generally not very reactive in the wine matrix. However, when oxygen is introduced to the wine, it reacts with metals to start a chain reaction that leads to the activation of the monomers, making them more likely to react with other monomers to reassemble tannin monomers into polymers. Each time two monomers (or a monomer and growing chain) bond, they become even more likely to bond again, leading to elongation of the tannin polymer. Put simply, activation by oxygen can begin a cascade that results in faster formations of phenolic polymers. These chains continue to grow, adding more phenolic subunits, until they bond with an anthocyanin. When an anthocyanin is added to the chain, it is not likely to bind with anything else, effectively capping the chain^2,3,5. 

   

Figure 1: Products of condensation reactions among tannin subunits differ based on the presence of oxygen. From: Micro-oxygenation A Treatsise (McCord)⁶”

These chain reactions of tannin molecules have important effects for the color and astringency of the wine. The perceived mouthfeel of tannins is, in part, related to the length of the phenolic chains. Longer chains have more reactive sites for interaction with salivary proteins, thus the higher the degree of polymerization, the more astringent tannins seem. Micro-oxygenation soon after fermentation is thought to bind anthocyanins to growing chains before they are lost to precipitation, enzymatic attack or binding to lees, resulting in better color retention and shorter tannin polymers^1,7. Smith (2014) also claims that smaller polymeric chains form a finer-grained colloidal structure, leading to better flavor integration⁷. Polymeric pigments (tannin polymers capped with anthocyanins) are less susceptible to oxidation and browning than monomeric anthocyanins, so MOX also aids in in color stability by preserving anthocyanins in solution in their colored form³.

Micro-oxygenation also affects tannin perception through a side reaction with acetaldehyde.

When oxygen reacts with metals in the wine, it produces hydrogen peroxide which interacts with ethanol to form acetaldehyde. Acetaldehyde binds with anthocyanins, potentially forming more stable color molecules. It also allows bridging between tannin molecules that may alter the sensory characteristics of wine³. Specifically, cross-linked tannins have a more globular structure, and therefore less astringency. Some cross-linked tannins are prone to precipitate, further decreasing astringency⁴, but this would also lead to loss of color.

In addition to color stability and tannin structure, micro-oxygenation also has an effect on the perception of reduced compounds such as H₂S (sewer gas, rotten eggs) and methyl mercaptan (cabbage, skunk). Reduction is the chemical state of a compound whereby it has gained electrons in a reaction. Hydrogen atoms only hold their electrons weakly, so when they are bonded to sulfur atoms, the electrons spend more time near the sulfur, resulting in a reduced sulfur compound. Oxygen atoms on the other hand are strong electron attracters, so when oxygen is added to a solution with reduced sulfur compounds, some of the electrons will be attracted to the oxygen atoms and leave the sulfur atom, thereby oxidizing the compound. Oxidation of hydrogen sulfide results in two odorless compounds (water and elemental sulfur). Oxidation of methyl mercaptan results in dimethyl sulfide, which still has off odors of onion and garlic, but at a higher threshold of detection (12 ppb vs. 0.2-2 ppb)^1,8.

When it was first introduced, reports showed that micro-oxygenation also led to significant decreases in the sensory perception of herbal/vegetal character in wine. However, repeated measurement of the chemical methoxypyrazine, a principle chemical component of “veggie”, did not change. Further study revealed that the perception of “veggie” included a combination of pyrazine as well as some reduced sulfur compounds (AKA thiols) with vegetal aromas (such as canned green beans). The reduction of the perception of “veggie” after micro-oxygenation was due to oxidation of these reduced compounds^8,9.

Figure 2: from Enology Notes #134, Zoecklein (2007)⁹

Risks of micro-oxygenation

Despite its potential benefits, micro-oxygenation has some risks. Allowing micro-oxygenation to go on too long can lead to excessive polymerization, making tannins dry and harsh⁸. Oxygenation at too high of a rate can cut off the chain reaction of polymerization by starting too many chains at once. Ultimately this leaves excess oxygen in the wine that reacts with anthocyanins to cause browning as well as varietal aromas and flavors, causing oxidative off odors². Oxygen availability in wine can also lead to microbial spoilage. Acetobacter will use available oxygen to produce acetic acid. Brettanomyces growth is facilitated by the presence of oxygen⁸(though it is thought that at low levels, micro-oxygenation poses less of a threat than standard racking⁴). Zoecklein ¹ likens the management of micro-oxygenation to piloting an ocean liner. It must be done carefully and pro-actively with the understanding that one action begets a chain reaction that is not easy to control or fully predict. A firm understanding of the underlying mechanisms at play and careful monitoring of progress are key to success.

How and when to micro-oxygenate

To micro-oxygenate wine, an oxygen supply (purchased from the gas supplier) is connected to a dosing chamber (such as the Stavin Ox Box). The dosing chamber acts as a high precision dosing regulator that can be set for very small amounts of oxygen flow. Oxygen exits the box through small tubing into miniature sparging tips with very small (10 um) pore size to produce very fine bubbles⁶. Soluble solids and lees have been shown to interfere with MOX effects¹⁰, and can contain spoilage microbes, so the tubing is configured so that the sparging tips are suspected about an inch above the bottom of the tank to avoid disturbing any remaining lees.

 

Figure 3: Schematic representation of a micro-oxygenation system. From Gomez-Plaza and Cano-Lopez (2010)⁴

MOX can be applied at any time during vinification and maturation, with total doses up to 600 mL/L for tannic red wines over the lifetime of the wine¹⁰. The effects of MOX will differ depending on the timing and dose rate of the addition.

Mox has been used during fermentation as a means to encourage yeast health and reduce off aromas during fermentation.

MOX prior to malolactic fermentation (MLF) has been shown to be effective in improving wine structure. Oxygen addition at this stage stimulates polymerization when tannins are most susceptible¹⁰. Shortly after the completion of alcoholic fermentation, anthocyanins and tannins are still in monomeric form, and thus in greatest need of oxygen for polymerization. Wine has greater reductive strength at this time since many potential binding sites for oxygen remain un-reacted. Dosage rates before malolactic fermentation can be 10 times higher than those after MLF, within a range of 20-60 mg/L/month for two to six weeks^10,11. MLF can be delayed with the addition of lysozyme or chitosan to allow enough time for MOX to proceed.

After malolactic fermentation, it is thought that at least some polymerization has already occurred, so MOX has less of an effect on tannin structure. In addition, at this point, some anthocyanins have been lost to enzymatic processes and interactions with lees. Due to the lesser number of free anthocyanins and monomeric phenols, lower doses of oxygen (1-5 mg/L/month for up to 3 months) are used at this stage. In addition, the threat of acetaldehyde accumulation is greater. Malolactic bacteria consume acetaldehyde, so accumulation after alcoholic fermentation is somewhat moderated by consumption at the end of malolactic fermentation. After MLF is complete, this is no longer an option. However, due to the high number of wines needing attention during harvest, applying MOX after MLF may be more practical. It is not uncommon for MOX to be done at higher rates before malolactic fermentation, stopped while malic acid bacteria are active, then applied again at lower rates after malic acid has been depleted^4,10. 

In addition to timing and dosage of oxygen addition, several other considerations come into play when planning micro-oxygenation treatment:

Continuous vs. discontinuous: Supplying a higher rate of oxygen all at once may not have the same effect as supplying it over the entire course of the month. Singleton (1987) found that “slow oxidation does not exhaust the original oxidizable substrates of wine as rapidly as does fast oxidation”². Practically, this means that slow oxidation gives wine greater reductive strength, making it less susceptible to oxidation later while avoiding oxidation of flavor and aroma compounds as well as color^1,2. Slow delivery also allows the utilization of one day’s oxygen prior to addition of the next day’s dose¹².  For these reasons, constant oxygenation is safer than discontinuous application since flow rates are slower and monitoring is easier to follow. 

Based on the flow rates of the equipment, however, it may not be possible to dose the wine continuously, especially in the post-MLF treatment. If using the Stavin Ox Box (as in the experiments conducted at Michael Shaps Wineworks), the meter on the box cannot measure below 0.25 ml/L/minute. For a tank containing 2100 L (555 gallons) of wine, the box would need to be set at 0.15 mL/minute to achieve a target median post-ML flow rate of 3 mg O₂/L/month⁶. It is possible to deliver this flow rate in an episodic manner instead, dosing at a higher dose for less time to hit the same overall target dose. Periodic oxygenation is closer to what wine would experience by standard aging in a barrel⁶. 

Path height: A minimum path length of 2.2 – 4 m (depending on the dosage) is required in order to fully dissolve oxygen in the wine and not increase oxygen in the headspace using a traditional MOX unit¹³. Barrel adaptations have been made that allow MOX with a shorter path length.

Temperature: Temperature is an important variable for MOX. Warmer temperature leads to lower solubility of oxygen and more buildup in the headspace. Colder temperature slows down oxidation and polymerization reactions. A temperature near 15°C (within a range of 14-17°C ) is recommended as a good compromise¹⁰.

Turbidity: Soluble solids and lees can contain spoilage microbes such as Acetobacter and Brettanomyces that will consume oxygen and produce off flavors and odors. Wines should be racked carefully off lees with a target of <100 NTU prior to treatment¹⁰.

SO2 level: SO₂ will somewhat slow the effects of MOX¹⁴, but it will also help protect the wine from severe oxidation¹⁰. If SO₂ is present, it should not exceed 25 ppm free SO₂. 

Monitoring the progress of micro-oxygenation

Micro-oxygenation follows the goldilocks principle. If you do not add enough oxygen you will not see the benefits. If you push it too far, you can end up with dry tannins and oxidized wine. How can you tell when your oxygen dose and duration are “just right”? There are several measurements for monitoring the progress of MOX. 

Dissolved oxygen (DO) is a useful monitoring tool, as long as the measurement is taken from the tank without introducing additional oxygen. If the dosage of oxygen is set correctly, most of the oxygen should be bound by phenolics rather than remaining dissolved or filling the headspace. High DO rates indicate MOX is set too high for the wine. Measuring DO before and after treatment can give an indication if the dose rate is too high¹⁰.

Volatile acidity (VA) is another endpoint used to monitor progress. Acetic acid bacteria utilize excess DO to produce acetic acid, causing a spike in VA. This indicates that oxygen dose rate is too high and is a warning sign of wine spoilage. 

Acetaldehyde buildup will also indicate that oxygen rates may be too high. Enzymatic kits for testing acetaldehyde using a spectrophotometer can be purchased from enological companies (for example, Unitech sells 20 tests for $65.00). If a spectrophotometer is not available, McCord⁶ suggests a test comparing a fresh glass of wine with one that has been sitting out covered by a watchglass overnight. Excess acetaldehyde has sensory effects of rotten apples or a sherry-like quality¹⁵. If acetaldehyde is detected in both samples, then the rate of oxygenation is too high. If the overnight sample smells of pumpkin or chocolate, but the fresh sample does not, the rate is good. If there is no difference between the two glasses, then the rate should be increased.

In wines treated with micro-oxygenation after malolactic fermentation, free SO₂ has been found to be an effective monitoring tool. SO₂ rates should stay above 10 ppm to avoid oxidation⁴. If SO₂ decreases too rapidly, then the O₂ dose is too high.  

Careful sensory analysis throughout the experiment is a key tool to determining if acetaldehyde is building up, if Brettanomyces or Acetobacter have taken hold, if reduction is diminishing, and how the tannins are evolving. 

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References

(1) Zoecklein, B. W. Winemaking Topics; Micro-Oxygenation. Virginia Tech Wine/Enology Grape Chemistry Group, n.d.

(2) Singleton, V. L. Oxygen with Phenols and Related Reactions in Musts, Wines, and Model Systems: Observations and Practical Implications. 1987, 38 (1), 69–77.

(3) Waterhouse, A. L.; Laurie, V. F. Oxidation of Wine Phenolics: A Critical Evaluation and Hypotheses. American Journal of Enology and Viticulture 2006, 57 (3), 306–313.

(4) Gómez-Plaza, E.; Cano-López, M. A Review on Micro-Oxygenation of Red Wines: Claims, Benefits and the Underlying Chemistry. Food Chemistry 2011, 125 (4), 1131–1140. 

(5) Fulcrand, H.; Dueñas, M.; Salas, E.; Cheynier, V. Phenolic Reactions during Winemaking and Aging. American Journal of Enology and Viticulture 2006, 57 (3), 289–297.

(6) McCord, J. Micro-Oxygenation: A Treatise. Stavin, 2009.

(7) Smith, C. Postmodern Winemaking: Rethinking the Modern Science of an Ancient Craft by Clark Smith (7-Jan-2014) Hardcover; University of California Press, 2014.

(8) Zoecklein, B. W. Current Theory and Applications: Microoxygenation. Practical Winery and Vineyard2007, November/December.

(9) Zoecklein, B. W. Factors Impacting Sulfur-like Odors in Wine and Winery Operations Part 2. Enolgoy Notes #134, 2007.

(10) Lesica, M.; Košmerl, T. Microoxygenation of Red Wines. Acta agricultura Slovenica 2009, 93 (3), 327–336.

(11) Gomez-Plaza, E.; Gil, R.; Lopez-Roca, J.; Adrian, M. Effects of the Time of SO2 Addition on Phenolic Compounds in Wine. Vitis -Geilweilerhof- 2001, 40, 47–48.

(12) Smith, C. MIcro-Oxygenation. Vinovation, n.d.

(13) Durner, D.; Ganss, S.; Fischer, U. Monitoring Oxygen Uptake and Consumption during Microoxygenation Treatments before and after Malolactic Fermentation. Am. J. Enol. Vitic. 2010, 61 (4), 465–473.

(14) Gambuti, A.; Han, G.; Peterson, A. L.; Waterhouse, A. L. Sulfur Dioxide and Glutathione Alter the Outcome of Microoxygenation. American Journal of Enology and Viticulture 2015, 66 (4), 411–423.

(15) Thomas, T. What’s in Wine: Acetaldehyde. Waterhouse Lab, UC Davis, 2004.

On Feb 11, 2021, winemakers from around Virginia gathered (virtually) to discuss results of two experiments. In the first, Nate Walsh from Walsh Family Wine tested the effects of using stabularion on the aromatic complexity of his Sauvignon Blanc. In the second, Michael Heny from Michael Shaps Wineworks explored the effects of micro-oxygenation on a Cabernet Sauvignon wine prone to reduction during fermentation.

 

Watch Video

Summary

This study examines the impact of micro-oxygenation in aging Tannat wine.  Tannat wine was split into two identical tanks.  The treatment tank was micro-oxygenated with a dosing stone through a Stavin Ox Box.  Due to the small volume of wine, continuous micro-oxygenation was not possible, and instead a discontinuous regimen was put in place with a target oxygen rate of 5 mL O₂/L wine/month.  This was achieved by dosing the wine with 0.61mL O₂/minute for approximately 10 hours every 3-5 days.  Treatment was halted when malolactic conversion began.  Chemistry results were not too different, except for sulfur dioxide binding (where more sulfur dioxide was binding in the control).  Sulfides were not very different, and differences in Oenococcus are likely not due to the treatment.  Color was not very different.  The micro-ox wine had higher levels of anthocyanins, but slightly lower polymeric pigment and tannin.  For the triangle test, of 27 people who answered, 5 people chose the correct wine (19%), suggesting that these wines were not significantly different.  In fact, this suggests that judges consistently and significantly did not choose the correct wine and were biased to the replicates (p<0.05).  In general, of people who answered correctly, 3 preferred the micro-ox wine, and 2 preferred the control wine.  For the descriptive analysis, there were no strong trends for the descriptors used in this study.  There may have been a slight tendency for the micro-ox wine to have higher Astringency, but this was very weak.  These kinds of studies should be repeated in the future, over multiple varieties, utilizing both continuous and discontinuous micro-oxygenation schemes.  Furthermore, more intensive micro-oxygenation regimens should be performed in future studies.

Introduction

Just after completion of red wine fermentation, limited oxygen exposure may have beneficial impacts on red wine phenolic attributes, such as by enhancing color stability, softening tannin, and providing body (Zoecklein 2001a).  Aeration can also help if done during alcoholic fermentation (macro-oxygenation), it can help reduce reductive aromas (although sometimes it may not effectively combat reduction), and integrate overall aromatic quality of the wine (Zoecklein 2000).  Aeration both during and after fermentation can promote the formation of polymeric pigment, stabilizing color.  Aeration is more beneficial at this point due to the higher levels of phenolic compounds in the wine and the greater protection of the wine at this stage due to negative oxidation reactions.  Oxidation reactions are promoted in both rate and extent by higher pH, and the formation of acetaldehyde through oxygenation can promote tannin-anthocyanin bridging resulting in stable pigment.  The presence of sulfur dioxide can result in acetaldehyde binding, which may inhibit the formation of these acetaldehyde-based polymeric pigments.  Thus, it is often recommended that sulfur dioxide be kept low during the course of micro-oxygenation treatments (Zoecklein 2001a).  Research by Patrick Sullivan has suggested that micro-oxygenated wines had greater perceptions of fruit intensity, plushness, and less vegetative aromas (Zoecklein 2001b).  The purpose of the present study is to investigate the role of micro-oxygenation in helping to age Tannat wine.

Results and Discussion

Chemistry results were not too different, except for sulfur dioxide binding (where more sulfur dioxide was binding in the control).  Sulfides were not very different, and differences in Oenococcus are likely not due to the treatment.  Color was not very different.  The micro-ox wine had higher levels of anthocyanins, but slightly lower polymeric pigment and tannin.  For the triangle test, of 27 people who answered, 5 people chose the correct wine (19%), suggesting that these wines were not significantly different.  In fact, this suggests that judges consistently and significantly did not choose the correct wine and were biased to the replicates (p<0.05).  In general, of people who answered correctly, 3 preferred the micro-ox wine, and 2 preferred the control wine.  For the descriptive analysis, there were no strong trends for the descriptors used in this study.  There may have been a slight tendency for the micro-ox wine to have higher Astringency, but this was very weak.  These kinds of studies should be repeated in the future, over multiple varieties, utilizing both continuous and discontinuous micro-oxygenation schemes.  Furthermore, more intensive micro-oxygenation regimens should be performed in future studies.

 

Methods

Tannat grapes from the Honah Lee vineyard were crushed and destemmed into tank, inoculated with RBS133 yeast and allowed to undergo fermentation under standard conditions. Superfood and DAP were added as necessary. When fermentation was complete, wine was pressed off skins and seeds, and transported from the Wineworks satellite location to the Harris Creek Location.  Wine was allowed to settle after transport, then racked into two 1200 L tanks, splitting the lot into control and treatment. NTU was measured at 46 and DO was measured for the control tank at 0.47 and 0.32 for the treatment tank.  An NTU  less than 200 was desired to prevent aerative spoilage organisms and particulate binding sites for oxygen.  Glycol was set to 55 degrees on each tank and temperature was tested prior to each oxygen dose.  Lead lines from the Stavin Ox Box were threaded into the treatment tank so that dosing stones were suspended 1 inch from the bottom of the tank (to avoid lees).  Lines remained in place for the duration of the experiment to avoid oxygen addition from disturbing the surface.

Due to the small volumes of each tank (1125 L), continuous dosing was not possible from the Ox Box.  Instead, a discontinuous rate was set targeting 5 mL/L/month, at a dose rate of 0.61 mL/min for 10 hours every 3-5 days.  Temperature was checked prior to each oxygen dose. Dissolved oxygen was checked before and after each dose. Throughout the experiment, both lots were tested weekly for sensory attributes (specifically tannin structure, offensive odors, and oxidation), sulfur dioxide levels (which should be very low), and VA. Malic acid was checked once per week. Treatment was halted when malolactic fermentation began in one tank. The other tank was then inoculated for malolactic fermentation.  After malolactic fermentation was complete, sulfur dioxide was added and wine was racked to barrel for aging.

These wines were tasted on May 30.  For the triangle test, descriptive analysis, and preference analysis, anybody who did not answer the form were removed from consideration for both triangle, degree of difference, and preference.  Additionally, anybody who answered the triangle test incorrectly were removed from consideration for degree of difference and preference.  Additionally, any data points for preference which did not make sense (such as a person ranking a wine and its replicate at most and least preferred, when they correctly guessed the odd wine) were removed.  

In order to balance the data set to perform statistical analysis for descriptive analysis, any judge who had not fully completed the descriptive analysis ratings were removed.  In order to then make the number of judges between groups equivalent, one judge from group 1 was transferred to group 3, and another judge from groups 1 and 2 were eliminated.  This resulted in a final data set of 3 groups, each with 6 judges (considered as replications within groups, and groups were considered as assessors).  Data was analyzed using Panel Check V1.4.2.  Because this is not a truly statistical set-up, any results which are found to be statistically significant (p<0.05) will be denoted as a “strong trend” or a “strong tendency,” as opposed to general trends or tendencies.  The statistical significance here will ignore any other significant effects or interactions which may confound the results (such as a statistically significant interaction of Judge x Wine confounding a significant result from Wine alone).  The descriptors used in this study were Fruit Intensity, Herbaceous/Green, Overall Aromatic Intensity, Bitterness, Astringency, and Body.

 

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References

Zoecklein, B. 2000. Vintner’s corner: Microoxygenation. Vol 15, No. 2.  http://www.apps.fst.vt.edu/extension/enology/VC/MARAPR00.html. Accessed 5/31/2018.

Zoecklein, B. 2001a. Enology Notes #33: Controlled aeration of red wines.  http://www.apps.fst.vt.edu/extension/enology/EN/33.html.  Accessed 5/31/2018.

Zoecklein, B. 2001b. Vintner’s corner: Microoxygenation research. Vol 16, No. 6.  http://www.apps.fst.vt.edu/extension/enology/VC/Nov-Dec01.html#Micro. Accessed 5/31/2018.

Summary

This study examines the effect of different rates of macro-oxygenation on the phenolic and sensory qualities of Cabernet Franc.  Grapes were harvested on the same day but kept separate, and all treatments between lots were kept the same except that one T Bin received no macro-oxygenation, one T Bin received a rapid macro-oxygenation to attain 5mg/L added oxygen after punchdowns (<1 hour aeration), and another T Bin received a slow aeration to attain 5mg/L added oxygen after punchdowns (3-4 hours aeration).  Oxygen was added after punchdowns.  No major chemical or phenolic differences are noticeable between treatments, except that phenolics slightly decreased in aerated wines.  Macro-oxygenation tended to lower Overall Aromatic Intensity, with rapid macro-oxygenation tending to lower it the most.  There were slight tendencies for macro-oxygenation to increase oxidation qualities and lower Fruit Intensity, and rapid macro-oxygenation tended to have slightly higher Bitterness/Astringency.  These tendencies, however, were very weak.  In general, people tended to prefer wine made without macro-oxygenation, and least preferred the wine made with rapid macro-oxygenation.  Because these trends were very weak, this study should be repeated a few more times before making strong conclusions about macro-oxygenation.

 

Introduction

Different oxygenation regimes during fermentation are thought to affect the phenolic extraction, structure, and stability of finished wine.  Aerating red wines during and after fermentation increases the amount of polymeric pigment in wines.  Aerating younger wines tends to be more effective than older wines, since in younger wines the majority of phenolic compounds are still monomeric.  However, too much aeration in a wine’s life (especially later in its life) can cause precipitation of polymeric pigments and tannin (Zoecklein 2001).  Thus, finding ways to control the rate and timing of oxygenation throughout a wine’s life is very important to achieving high quality wines.

Macro-oxygenation during fermentation may be a technique to alter these factors with greater control.  Macro-oxygenation can be performed as a “single dose”, bringing in around 6mg/L oxygen to fermenting must in a period of 1-4 hours.  It can also be performed continuously, at 0.5mg/L per hour between 1.080 and 1.020 density (Deltel 2007).  

Must exposed to oxygenation during fermentation often shows decreased levels of anthocyanins (Cheynier et al 1997), but it is unclear if this is due to increases in yeast population which binds anthocyanins or due to enzymatic oxidation.  Additionally, exposing non-sulfited must to oxygenation early on results in losses of anthocyanins, phenolics, and hydroxycinnamic acids.  This study did not investigate the formation of polymeric pigment, however (Castellari et al. 1998).  

Most oxygen during macro-oxygenation is consumed by the yeast (Deltel 2007).  However, this aspect may also cause blooms of unwanted bacteria and yeast species, and may increase volatile acidity.  For example, aeration of wines which have an inoculum of Brettanomyces can promote growth (Zoecklein 2004), although this is commonly a concern towards the end of fermentation and during aging.  Macro-oxygenation may help reduce sulfur off odors during fermentation without reducing fruit aromas or oxidizing the wine (Deltel 2007).  However, it is very likely that aeration can also help keep sulfur compounds in solution, temporarily oxidizing these compounds to their less volatile disulfide forms.  This study examines the impact of different macro-oxygenation regimes during fermentation on these aspects in Cabernet Franc.

 

Results and Discussion

No major chemical or phenolic differences are noticeable between treatments, except that phenolics slightly decreased in aerated wines.

This project was tasted on March 8 and March 15.  Descriptive analysis on March 8 found that the wine produced with no macro-oxygenation showed a strong tendency to be higher in Overall Aromatic Intensity than the wines produced with macro-oxygenation.  Slow macro-oxygenation had higher Overall Aromatic Intensity than fast macro-oxygenation, but this was a weak trend.  No other major trends could be seen.  In general, people tended to prefer the wine produced from fast macro-oxygenation the least.

For the March 15 tasting, no major trends could be seen with the descriptors used in this study.  Fast macro-oxygenation tended to slightly increase Bitterness/Astringency, and macro-oxygenation in general tended to slightly increase Oxidation characteristics and lower Fruit Intensity.  In general there was a slight preference for wine which had not been macro-oxygenated.  The wine which underwent rapid macro-oxygenation was the least preferred.

In general, macro-oxygenation tended to lower Overall Aromatic Intensity, with rapid macro-oxygenation tending to lower it the most.  There were slight tendencies for macro-oxygenation to increase oxidation qualities and lower Fruit Intensity, and rapid macro-oxygenation tended to have slightly higher Bitterness/Astringency.  These tendencies, however, were very weak.  In general, people tended to prefer wine made without macro-oxygenation, and least preferred the wine made with rapid macro-oxygenation.  Because these trends were very weak, this study should be repeated a few more times before making strong conclusions about macro-oxygenation.

 

Methods

A lot of Cabernet Franc grapes from the same block were harvested on 10/5 and stored overnight in refrigeration.  The grapes were destemmed and crushed together, and placed into three separate but identical fermentation T-bins at 5.4hL per T-bin.  On during processing 6g/hL sulfur dioxide, 30mL/T Color Pro, 40g/hL FT Rouge, and 0.5g/L tartaric acid.  On 10/7, 10% of the must volume was removed through saignée to reduce the must volume to 4.9hL/T-bin.  These bins underwent a 2 day cold soak and were inoculated with 20g/hL Premier Cru Yeast on 10/8.  All fermentation practices, additions, punchdowns, etc. were identical between tanks.  The musts were chaptalized on 10/12 with 1.11kg/hL sugar.  The treatments for each T bin were as follows:

 

1. T Bin 1 : Control: 2 Punch Down / Day (no air)
2. T Bin 2 : Rapid Aeration: 2 Punch Down / Day. Addition (<1hours) of 5mg/L O2 / PD  up to approximately 1.060 specific gravity. (addition of O2 after PD)
3. T Bin 3 : Slower Aeration: 2 Punch Down / Day. Addition (3-4hours) of 5mg/L O2 / PD up to approximately 1.060 specific gravity. (addition of O2 after PD)

 

These treatments were achieved by bubbling ambient air (room air) through a stone into the wine after each punchdown to achieve 5mg/L dissolved oxygen until the wine reached a specific gravity of approximately 1.060.  Oxygenation was terminated after the first punchdown on 10/12.  Dissolved oxygen was not measured.

Maceration continued for the same amount of time between treatments, and all three bins were pressed separately on the same day (10/26) and drained into separate aging vessels.  Free run and press fractions were mixed for each project.  

Once separated into their barrels, the wine was treated with 0.8g/L tartaric acid and inoculated with malolactic bacteria on 10/27.  0.3mL/L lactic acid was added to the aging wines on 11/9.  Malolactic fermentation completed on 11/15/2016, upon which the wine was microbially stabilized with 55ppm sulfur dioxide.  All other treatments between vessels such as rackings, stirrings, etc. were identical.  

In order to balance the data set to perform statistical analysis for descriptive analysis on the March 8 tasting, any judge who had not fully completed the descriptive analysis ratings were removed.  In order to then make the amount of judges between groups equivalent, one judge from group 1 was transferred to group 3, and another judge from group 2 was eliminated.  This resulted in a final data set of 3 groups, each with 10 judges (considered as replications within groups, and groups were considered as assessors).  Data was analyzed using Panel Check V1.4.2.   Because this is not a truly statistical set-up, any results which are found to be statistically significant (p<0.05) will be denoted as a “strong trend” or a “strong tendency,” as opposed to general trends or tendencies.  The statistical significance here will ignore any other significant effects or interactions which may confound the results (such as a statistically significant interaction of Judge x Wine confounding a significant result from Wine alone).   The descriptors used in this study were Fruit Intensity, Herbaceous/Green, Overall Aromatic Intensity, Reduced/Oxidized (on a scale from most reduced to most oxidized), Bitterness, and Body.  

The same procedures for data analysis were used on the March 15 tasting.  For the descriptive analysis in this tasting, one judge had to be removed from group 3 to result in each group having 8 judges.

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References

Cheynier, V., Arellano, I.H., Souquet, J.M., and Moutounet, M. 1997. Estimation of the oxidative changes in phenolic compounds of Carignane during winemaking. Am. J. Enol. Vitic. 48:225-228.

Castellari, M., Arfelli, G., Riponi, C., and Amati, A. 1998. Evolution of phenolic compounds in red winemaking as affected by must oxygenation. Am. J. Enol. Vitic. 49:91-94.

Deltel, D. 2007. Bonnes Pratiques de Macro-oxygénation. Etude d’un cas concret pour les vins rouges. Revue des Œnologues N°125S. November.

Zoecklein, B. 2001. Controlled aeration of red wines. Enology Notes #33.  http://www.apps.fst.vt.edu/extension/enology/EN/33.html.

Zoecklein, B. 2004. Brettanomyces.  Enology Notes #92.  http://www.apps.fst.vt.edu/extension/enology/EN/92.html

 

Summary

This study examines the effect of oxygenation on wines.  Cabernet Sauvignon grapes were harvested and, after completion of fermentation, wine was drained and pressed into two tanks.  One tank was a control, and one tank received 40 mL O­₂/L wine/month for 3 days, and this rate was then halved every 3 days until after malolactic conversion began, where it received micro-oxygenation at 0.5 mL O­₂/L wine/month.  A third set of grapes from the same block were picked 5 days later (after a large rain event), and then received flash détente.  Since malolactic conversion completed so quickly for this treatment, its oxygenation could only be at 40mL O­₂/L wine/month for three days after draining and pressing before switching to 0.5 mL O­₂/L wine/month.  The treatments between the control and oxygenated wines were similar, but the vinification of the flashed wine was different, marked by 10 days of fermentation (compared to 14 days for the other treatments, including a 3 day cold soak).  The flashed wine also had slightly different additions made.  No major differences are found in wine chemistry between the control and oxygenation treatment, except for slightly higher lactic acid in the treatment.  The flashed wine had higher acidity, possibly due to differential tartrate adds.  The oxygenated wine had higher rates of S. cerevisiae and several Lactobacillus species relative to the control, but lower acetic acid bacteria.  The flashed wine had much lower levels of acetic acid bacteria and Lactobacillus, and lower levels of S. cerevisiae as well.  However, it was higher in O. oeni.  Color intensity lowered among the wines from November to April; however, the oxygenated wine may have had a slight increase in color intensity relative to the control over this time (although this was weak).  The oxygenated treatment had higher color intensity than the control, and the flashed wine was highest.  Phenolic parameters generally decreased from November to April, and oxygenation did not appear to have much effect on the phenolic parameters.  The flashed wine was much higher in catechin and quercetin and was also higher in tannin.  Although it was initially lower in anthocyanin (and higher in polymeric pigment), it ended up being higher in anthocyanin.  

For the triangle test, of 26 people who answered, 12 people chose the correct wine (46%), suggesting that the wines were not significantly different.  In general, people who answered correctly tended to prefer the oxygenated wine, although the preference trends were somewhat complex.  For the descriptive analysis, there was a strong trend for the flashed wine to have higher overall aromatic intensity than the other wines (LSD=0.97).  There was a slight trend for this wine to have higher Fruit Intensity and Body, and perhaps slightly lower Herbaceous/Green character (although it was similar to the oxygenated wine in this regard).  The control wine tended to have higher Herbaceous/Green character, lower Overall Aromatic Intensity, and higher Astringency (although equal to Flash in this regard).  The oxygenated treatment tended to have lower Bitterness and Astringency, and perhaps lower Body as well.  More studies should be performed on oxygenation, with regard to timing, amount, and with regard to continuous vs discontinuous oxygenation.

Introduction

Different oxygenation regimes during fermentation are thought to affect the phenolic extraction, structure, and stability of finished wine. Aerating red wines during and after fermentation increases the amount of polymeric pigment in wines. Aerating younger wines tends to be more effective than older wines, since in younger wines the majority of phenolic compounds are still monomeric. However, too much aeration in a wine’s life (especially later in its life) can cause precipitation of polymeric pigments and tannin (Zoecklein 2001a). Thus, finding ways to control the rate and timing of oxygenation throughout a wine’s life is very important to achieving high quality wines.

Macro-oxygenation during fermentation may be a technique to alter these factors with greater control. Macro-oxygenation can be performed as a “single dose”, bringing in around 6mg/L oxygen to fermenting must in a period of 1-4 hours. It can also be performed continuously, at 0.5mg/L per hour between 1.080 and 1.020 density (Deltel 2007). 

Must exposed to oxygenation during fermentation often shows decreased levels of anthocyanins (Cheynier et al 1997), but it is unclear if this is due to increases in yeast population which binds anthocyanins or due to enzymatic oxidation. Additionally, exposing non-sulfited must to oxygenation early on results in losses of anthocyanins, phenolics, and hydroxycinnamic acids. This study did not investigate the formation of polymeric pigment, however (Castellari et al. 1998). 

Most oxygen during macro-oxygenation is consumed by the yeast (Deltel 2007). However, this aspect may also cause blooms of unwanted bacteria and yeast species and may increase volatile acidity. For example, aeration of wines which have an inoculum of Brettanomyces can promote growth (Zoecklein 2004), although this is commonly a concern towards the end of fermentation and during aging. Macro-oxygenation may help reduce sulfur off odors during fermentation without reducing fruit aromas or oxidizing the wine (Deltel 2007). However, it is very likely that aeration can also help keep sulfur compounds in solution, temporarily oxidizing these compounds to their less volatile disulfide forms.

Just after completion of red wine fermentation, limited oxygen exposure may have beneficial impacts on red wine phenolic attributes, such as by enhancing color stability, softening tannin, and providing body (Zoecklein 2001a).  Aeration can also help reduce reductive aromas (although sometimes it may not effectively combat reduction), and integrate overall aromatic quality of the wine (Zoecklein 2000).  Aeration both during and after fermentation can promote the formation of polymeric pigment, stabilizing color.  Aeration after completion of fermentation is often referred to as micro-oxygenation.  Aeration is more beneficial at these points due to the higher levels of phenolic compounds in the wine and the greater protection of the wine at this stage due to negative oxidation reactions.  Oxidation reactions are promoted in both rate and extent by higher pH, and the formation of acetaldehyde through oxygenation can promote tannin-anthocyanin bridging resulting in stable pigment.  The presence of sulfur dioxide can result in acetaldehyde binding, which may inhibit the formation of these acetaldehyde-based polymeric pigments.  Thus, it is often recommended that sulfur dioxide be kept low during the course of micro-oxygenation treatments (Zoecklein 2001a).  Research by Patrick Sullivan has suggested that micro-oxygenated wines had greater perceptions of fruit intensity, plushness, and less vegetative aromas (Zoecklein 2001b).  The purpose of the present study is to investigate the role of oxygenation in helping to age Cabernet Sauvignon wine.

Results and Discussion

No major differences are found in wine chemistry between the control and oxygenation treatment, except for slightly higher lactic acid in the treatment.  The flashed wine had higher acidity, possibly due to differential tartrate adds.  The oxygenated wine had higher rates of S. cerevisiae and several Lactobacillus species relative to the control, but lower acetic acid bacteria.  The flashed wine had much lower levels of acetic acid bacteria and Lactobacillus, and lower levels of S. cerevisiae as well.  However, it was higher in O. oeni.  Color intensity lowered among the wines from November to April; however, the oxygenated wine may have had a slight increase in color intensity relative to the control over this time (although this was weak).  The oxygenated treatment had higher color intensity than the control, and the flashed wine was highest.  Phenolic parameters generally decreased from November to April, and oxygenation did not appear to have much effect on the phenolic parameters.  The flashed wine was much higher in catechin and quercetin and was also higher in tannin.  Although it was initially lower in anthocyanin (and higher in polymeric pigment), it ended up being higher in anthocyanin.  

For the triangle test, of 26 people who answered, 12 people chose the correct wine (46%), suggesting that the wines were not significantly different.  In general, people who answered correctly tended to prefer the oxygenated wine, although the preference trends were somewhat complex.  For the descriptive analysis, there was a strong trend for the flashed wine to have higher overall aromatic intensity than the other wines (LSD=0.97).  There was a slight trend for this wine to have higher Fruit Intensity and Body, and perhaps slightly lower Herbaceous/Green character (although it was similar to the oxygenated wine in this regard).  The control wine tended to have higher Herbaceous/Green character, lower Overall Aromatic Intensity, and higher Astringency (although equal to Flash in this regard).  The oxygenated treatment tended to have lower Bitterness and Astringency, and perhaps lower Body as well.  More studies should be performed on oxygenation, with regard to timing, amount, and with regard to continuous vs discontinuous oxygenation.

Methods

Cabernet Sauvignon grapes from the same block were harvested, destemmed, and crushed into one tank on October 8, 2017 for cold soak and fermentation.  At this time, the musts received 40ppm sulfur dioxide, 83g Lafase Fruit, 40g/hL Tanin VR Supra, and 2g/L Boise Frais.  Both tanks received a 3 day cold soak (and received 100g/hL tartaric acid on the third day), were then warmed for a day, and inoculated the following day with F15 at 15g/hL with GoFerm at 20g/hL.  On October 18, 50g/hL tartaric acid was added as well.  Wines were drained and pressed on October 25, and two days later were racked into stainless steel tanks.  At this racking, the treatment block was split off from the control.  The control wine was racked again on October 30, and malolactic conversion commenced.  The control wine was racked and returned after the completion of malolactic conversion (November 29), and 50ppm sulfur dioxide was added.  An additional 50ppm sulfur dioxide was added to the control 2 days later.  On January 12, 20ppm sulfur dioxide was added to the control wine.

The Oxygenated treatment was also racked on October 30 and November 29.  It was then racked into a different aging vessel on January 18, and again on January 23.  On these days the wine received 24ppm and 13ppm sulfur dioxide adds, respectively.  

A third treatment, involving flash détente, was also used.  After about 1 inch of rain the remaining of the block was harvested and run through Flash Détente on October 13.  Due to the nature of Flash Détente, very different procedures were followed.  At crush, 10kg Tanin VR Color was added (in approximately 3215 Gallons of wine), 3mL/100kg Thermoliquide was added, and on the same day as crush F15 at 15g/hL with 20g/hL GorFerm.  Fermaid was added at 25g/hL on October 16, and on October 18 50g/hL tartaric acid was added.    The wine was drained and pressed on October 24 and racked twice over the next three days.  Malolactic fermentation occurred and completed on November 10, after which the wine was centrifuged an 60ppm sulfur dioxide was added.  On November 21, an additional 24ppm sulfur dioxide and 150g/hL Tartaric acid were added.  The wine was racked again on January 23.

Red wine phenolic panels were tested by an outside lab before malolactic conversion and post-malolactic conversion primarily looking for the tannin/anthocyanin ratio.  Dissolved oxygen was monitored occasionally in house. 

The treatments for each tank were:

1. Tank 1: Control: 2 Pump over/ Day (with air).  After primary fermentation Drain/Press and malolactic allowed to finish.
2. Tank 2: Oxygenation: 2 Pump over / Day (with air). After primary fermentation Drain/Press.  Oxygen rate 40 ml/l/month prior to malolactic fermentation for 3 days (beginning on October 27), then 20 ml/l/month for 3 days, then 10 ml/l/month for 3 days, then 5 ml/l/month for 3 days, then 2.5 ml/l/month for 3 days all depending on A/T ratio and reactive tannins.  Malolactic was allowed to finish, and afterwards post-malo oxygen rate was 0.5 ml/l/month
3. Tank 3: Flash + Macro Oxygenation: 2 Pump over / Day (with air). After primary fermentation Drain/Press.  Oxygen rate of 40 ml/l/month was prior to malolactic fermentation for 3 days (beginning on October 25).  Malolactic fermentation finished early, and right after the post-malolactic oxygen rate was 0.5 ml/l/month

These treatments were achieved by Vivelys Visio Oxygen diffuser through aeration stones placed into the bottom of the fermenters prior to filling.

All other treatments between wines were equal.

This study was tasted on May 30. For the triangle test and preference analysis, anybody who did not answer the form were removed from consideration for both triangle, degree of difference, and preference. Additionally, anybody who answered the triangle test incorrectly were removed from consideration for degree of difference and preference. Additionally, any data points for preference which did not make sense (such as a person ranking a wine and its replicate at most and least preferred, when they correctly guessed the odd wine) were removed. The flashed sample was ignored for triangle testing (but not for preference or descriptive analysis), and only the control vs the oxygenated samples were compared. 

In order to balance the data set to perform statistical analysis for descriptive analysis, any judge who had not fully completed the descriptive analysis ratings were removed. In order to then make the amount of judges between groups equivalent for the analysis which included the flashed wine, one judge from group 3 was eliminated. This resulted in a final data set of 3 groups, each with 6 judges (considered as replications within groups, and groups were considered as assessors). Data was analyzed using Panel Check V1.4.2. Because this is not a truly statistical set-up, any results which are found to be statistically significant (p<0.05) will be denoted as a “strong trend” or a “strong tendency,” as opposed to general trends or tendencies. The statistical significance here will ignore any other significant effects or interactions which may confound the results (such as a statistically significant interaction of Judge x Wine confounding a significant result from Wine alone). The descriptors used in this study were Fruit Intensity, Herbaceous/Green, Overall Aromatic Intensity, Bitterness, Astringency, and Body.

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References

Castellari, M., Arfelli, G., Riponi, C., and Amati, A. 1998. Evolution of phenolic compounds in red winemaking as affected by must oxygenation. Am. J. Enol. Vitic. 49:91-94. 

Cheynier, V., Arellano, I.H., Souquet, J.M., and Moutounet, M. 1997. Estimation of the oxidative changes in phenolic compounds of Carignane during winemaking. Am. J. Enol. Vitic. 48:225-228. 

Deltel, D. 2007. Bonnes Pratiques de Macro-oxygénation. Etude d’un cas concret pour les vins rouges. Revue des Œnologues N°125S. November.

Zoecklein, B. 2000. Vintner’s corner: Microoxygenation. Vol 15, No. 2.  http://www.apps.fst.vt.edu/extension/enology/VC/MARAPR00.html. Accessed 5/31/2018.

Zoecklein, B. 2001a. Enology Notes #33: Controlled aeration of red wines.  http://www.apps.fst.vt.edu/extension/enology/EN/33.html.  Accessed 5/31/2018.

Zoecklein, B. 2001b. Vintner’s corner: Microoxygenation research. Vol 16, No. 6.  http://www.apps.fst.vt.edu/extension/enology/VC/Nov-Dec01.html#Micro. Accessed 5/31/2018.

Zoecklein, B. 2004. Brettanomyces. Enology Notes #92. http://www.apps.fst.vt.edu/extension/enology/EN/92.html.