Micro-Oxygenation has been employed commercially in France as a wine treatment technique since 1991 when Patrick DuCournau began experimenting on the wines of Madiran in southwestern France. A decade later his company OenoDev has manufactured and placed several thousand units throughout the world to employ this technique under their guidance. The technique has attracted the attention of several U.S. wineries in recent years.
In 1998, OenoDev approached Vinovation to represent their products in the United States. We have used this opportunity to expand our team of enologists and work more closely with clients interested in expert support in the use of our tools (See "Practicing GrapeCraft" ). Micro-Ox has become for us the focal point of an integrated winegrowing philosophy. For the 1999 vintage we coordinated a collaborative scientific study involving eight of our winery partners which investigated the sensory and microbiological effects of the technique and the analytical differences which manifest themselves as a result of its use (results available on request).
In order to provide our customers with useful information on the technique, we compressed and translated OenoDev documentation into English. The translations are offered as an aid to our customers and may be imperfect. French originals are available as well.
The introduction of pure oxygen into wine is obviously hazardous to its quality. We urge our clients to act diligently to monitor the operation of their experimental equipment and its effects on wine. Most clients within our consulting spheres take advantage of our Full Service Support packages, which provide affordably whatever on-site expertise is required to assure good results and minimize risk.
Clients should anticipate a 3 to 5 year phase-in period before the full benefit of micro-oxygenation and related ιlevage techniques can be fully implemented. In the first year, the basic technique is performed on limited volumes of well-colored, low risk wine types to familiarize winery staff with the details of good work and to consider the technique's utility in the context of the winery's particular grape characteristics and marketing goals. Each year, volume and diversity of wine types is typically expanded. Once the educational and physical plant issues are overcome and the process is integrated into the winery's flow of work, the role of Vinovation's staff may be the surest and most economical option to support a large number of units.
OenoDev's basic claims, which at first seemed so outrageous, now are quite apparent to us. The careful, slow introduction of oxygen at properly maintained levels can build structure and longevity, enhance mouthfeel, delay tannic dryness during ageing, integrate vegetal aromas and tame reductive characters, including sulfides.
We still have much to learn, however. Each winery presents a different challenge. In one winery, we may be working toward rich, generous wines for early consumption. In another, our goal may be to protect and enhance the distinctive character and ageing potential of reserve wines. Our expertise is rapidly gaining breadth as we and our clients together gain experience with these products.
The exercise of investigating MicroOxygenation will also prove useful to use as an aid to better understanding of phenolic interactions in wine. In addition, it has prompted us to develop Vineyard Enology as a means to enhance the starting quality of wines we work with.
Clark Smith, President
25 August 2001
The purpose of micro-oxygenation is to bring about desirable changes in wine texture and aroma which cannot be obtained by traditional ageing techniques. The objectives of the process include improved mouthfeel (body and texture), enhanced color stability, increased oxidative stability, and decreased vegetative aroma.
As treatment proceeds, one eventually observes an augmentation of the aromatic intensity, a development of the complexity. The tannins are less hard and softer, the body of the wine is increased, and the wine=s mouthfeel is rounder. The herbaceous aromas and the reduction character vanish and the length may increase.
One should not, however, expect steady progress of the wine in the desired direction. To anticipate the wine=s development, it is useful to divide the progression of the wine to this goal into phases, which are discussed below.
PHASE OF STRUCTURATION
At the start, the wine has a closed, low intensity of aromatic expression. Tannins are aggressive and intense, but do not fill the mouth. These are appropriate characteristics for a treatable candidate wine, and going directly to barrel may miss an opportunity to foster improvement through oxygen addition in tank.
In the early stages of oxygen addition, however, the wine tends to go toward a more aggressive structure and less harmony. It is difficult to give an exact description of this phase because we have not yet found satisfactory analytical factors to help us evaluate the observed phenomena. The end of this phase of structuration is determined by the inversion of those tendencies: that is, the wine begins to soften. Vegetative aromatic characteristics at this point are also diminished.
The limit to structuration that can be achieved depends on:
The best time to start introducing oxygen is when the alcoholic fermentation is complete with or without lees, with or without cap. Lees will take up oxygen, however, so for red wines it is more effective to rack off lees when practical or at least to be sure they are well settled.
1. Initial condition of the wine
The more tannins and phenolic compounds in the subject wine at the start of the treatment, the longer the structuration phase will take and the greater the structuring effect.
Any practice or condition which diminishes phenols will lead to a diminution of the structuring effect by the micro-oxygenation, such as:
On the other hand, anything aiming at the reinforcing of the structure will increase the effect:
Wines might be divided into these four cases:
OenoDev contends that although having very prompt ML is perhaps interesting for practical reasons and to feel comfortable, it doesn=t make any sense regarding the maturation aspects. However, if rapid ML occurs, it can be beneficial to delay a little the sulfur addition, but it can also result in other problems. In any case the idea is at least to bring fairly big amounts of O2 ASAP without O2 accumulation. Depending on the wine, a range of 10 to 60 mg of O2 per liter per month is the recommended range prior to ML. During the ML is a very effective period for consuming the extra aldehyde. In maintaining a level which produces faint rather than gross aldehydic aroma, the winemaker can Asurf@ the aldehyde during this period and maximize the wine=s tannin-pigment complexation and color stability.
Later, it=s another question. After ML is complete, the oxygen addition is normally diminished to within a range from 0.5 to 10 ml/l/mo. SO2 has many quelling effects on oxygen=s influence (see below), and its addition causes the wine to enter a stage where more care is required to achieve optimum results.
Interestingly, after SO2 is added, the free SO2 should be stable and should not drop during treatment more than normally expected for bulk storage. Tracking the SO2 level is useful as an alarm, but it only indicates that we are in the conditions of micro-oxygenation (no O2 accumulation) which doesn=t mean that it=s the best rate for the wine. For instance, if the wine is cold (10oC), it is not advisable to bring a lot of oxygen even if the wine needs some.
Once the wine has completed ML, the ideal temperature range is between 59 and 65oF. If it cannot be controlled, then it=s safe to keep the level of oxygenation under the curve as shown in Figure 2.
2. Early commencement of treatment
The earlier the micro-oxygenation begins, the more accessible is the wine. If micro-oxygenation begins immediately after alcoholic fermentation, the wine is not yet fined, and a structuring phase of greater length and intensity may be expected.
3. Rate of oxygen addition
The more oxygen added, the more dramatic the results will be, as long as it stays under the capacity of consumption of the wine. Beyond that point, if there is an accumulation of dissolved oxygen, an early deterioration of the wine with a drying of the tannins will occur. It may be difficult to differentiate between the normal Ahardening@ that occurs during this phase and a drying of the tannins. In this situation, a check on the SO2 level, the evolution of the aromatic compounds, and the measure of the dissolved oxygen will enable you to determine if the process is occurring properly. Tasting training on recognition and objective evaluation of types of tannins is a useful aid in following the wine and assessing the proper rate of addition.
Determining the appropriate level of oxygenation
If treatment is begun prior to completion of ML, the starting point should be 10 ml/l/mo minimum for a weak wine, up to 60 or more for a strong dark extract. The level may then be adjusted so aldehyde is faintly but not excessively perceived. Measurement of aldehyde can be helpful but it=s not very easy to conduct because it=s not very stable, and must be measured very quickly.
4. Influence of temperature
The temperature has a double impact on structuration. There is a direct influence on the speed of the reactions leading to the structuring effect. Also, oxygen solubility increases with decreasing temperature. Taken together, these effects present a danger to wines oxygenated at low temperature. If the temperature decreases, one must stop the process or at least limit the addition of oxygen, to avoid the accumulation of dissolved oxygen. Since this process usually takes place in winter, this situation occurs very frequently.
5. Influence of free SO2
The SO2 reacts with the peroxide, the aldehyde and the anthocyanins, limiting the reaction of oxidation and condensation between the tannins and anthocyanins. A high level of free SO2 will therefore limit the structuring effect of the oxygenation. This phenomenon explains why one can see high effects of oxygenation on wine treated before the malolactic, which is when the SO2 has not yet been adjusted.
6. Influence of the aeration too violent
Structuration may fail to achieve its fullest potential and be limited in length and intensity when racking with aeration is employed during treatment.
PHASE OF HARMONIZATION
The harmonization phase contrasts with the structuration phase. It is the period of time going from the ageing to the bottling of the wine. We can call it the evolution phase of the wine, because the modifications occurring then are irreversible, as opposed to the first phase.
Establishing a Aperfect@ ageing in the wine through:
These objective are no different than those sought when wine is barreled down.
2. Influence of the structuration phase
The length of the harmonization phase is related to the structuration phase. The longer the structuring, the more necessary the phase of harmonization. As a rule of thumb, the harmonization phase should be twice as long as the structuration phase. However, violent oxygenations can be used to accelerate that period.
3. The harmonization
This phase is the most difficult to follow, because the wine at this time is the most sensitive and the phenomena less reversible. The risks are the development of dryness of the palate and/or the excessive maturity accompanied by loss of freshness and oxidized aromatic expression. Adherence to temperature recommendations is likewise most critical in this phase. These risks are especially high if the wine is weak.
The dose of oxygen usually does not go over 1 ml/liter/month. The effects of the variation of the dose are more crucial than during the structuration phase. A variation in dose between 0.5 ml/l/month and 1.0 ml/l/month can produce a very different reaction in the wine. As the dose is very low during this phase, there is little risk of the accumulation of dissolved oxygen, so the temperature level is not very important. However, high temperature results in fast evolution and therefore increases the risk of oxidation.
The ideal dose is determined by tasting, which looks for maximum aromatic benefit without causing dryness on the palate. As soon as the tannins begin to seem too dry, it is necessary to limit the oxygen or even to stop the micro-oxygenation. If micro-oxygenation is continued at this point, the result will be a wine that lacks in volume, becomes very flat, and the aromas of oxidation may appear irreversibly.
On the other hand, because the notion of hard tannins and dry tannins are very close, one can be confused. If the tannins are hard, it means that the wine needs some oxygen to soften them, and that the harmonization phase must continue. If the tannins are dry, it means the contribution of oxygen must be limited.
According to our definition of these terms, the onset of drying tannins is accompanied by a loss of body and richness, whereas hardening/softening of tannins generally follows this pattern:
One way to test the difference is to place a sample of the wine into a bottle. If the wine hardens in the bottle, it means that the harmonization phase should carry on. If the wine is stable in the bottle during the two weeks to one month after bottling, it means that the process has been sufficient.
The process of harmonizing can be accelerated by a violent addition of oxygen such as through a racking, to impart 1 ml/l all at once. Such operations can lead to a rapid evolution and can be useful when one doesn=t have time to finish the ageing gently.
Need in oxygen decreasing
Classic evolution of the wine during the harmonization phase.
Depending on the type of wine desired, you can choose the subject you want to work on: aromas, palate or tannins. You can also choose whether you want to age the wine over a period of, say, 18 months in barrels, or 6 months in the tank.
EVOLUTION OF THE CHARACTERS OF REDUCTION
1. Reduction taste - origin:
2. Reductive flavor expression - cause and solution:
When deprived of oxygen, a red wine has the tendency to develop some reduction taste. A wine can be reductive without showing reduction taste if a sufficient dose of oxygen is available. As soon as the oxygen is missing (in the bottle, for instance), the reductive taste will develop very quickly.
During the phase of structuration, micro-oxygenation will increase the power of reduction of the wine and decrease the expression of reductive tastes in the same time. During the harmonization, the reductive power disappears completely if the ageing is completed.
If the wine is bottled too soon, or if the tank is without aeration, as long as the reduction power is high, reductive flavors will be apparent.
Once the structuration phase is past, sulfides can be very effectively cleaned with late micro-oxygenation at a rate of 1 to 2.5 ml/L/month over a one to two week period.
DISCUSSION OF THE USE OF THE EQUIPMENT
1. General features
Micro-Oxygenation is not primarily intended for use with problem wines. It supplements rather than replaces the action of the barrel.
The ideal situation is to work with well-concentrated wines which need only to be stabilized (not remedially salvaged) and refined by prolonged ageing, so as to keep a good balance of structure to roundness.
Other ideal features include:
2. Importance of the temperature
The temperature of the wine is an essential parameter of micro-oxygenation. Ideally, it should be kept stable at around 15oC. The colder the wine is the more capable it is of dissolving the oxygen. On the other hand, the colder it is the slower the consumption of oxygen.
As oxygen is added, the combination of these two phenomena leads to the accumulation of dissolved oxygen in the wine. However, there are lesser quantities when the oxygen addition occurs at low temperature. If the oxygen is accumulated as dissolved oxygen in the wine, controlled oxidation is not then occurring, and some of the problems linked to oxygen addition may then appear.
If the temperature rises too high, oxygenation is less beneficial. Except during ML, the addition of oxygen must be not done at high temperature (>18oC).
3. Importance of the repartition of the oxygen
The effects of oxidation vary widely according to the quantity of oxygen available dissolved at a certain time. For example, bringing 1 ml/l all at once won=t have the same effects as bringing it during one month. By metering in small quantities of oxygen, we want to promote some reactions which occur preferentially, while still avoiding others which are less energetically preferred. This partitioning balance point will be different in each case.
Moreover, the wine ages with or without oxygen. Some sort of reactions of condensation and precipitation (setting) will proceed with time, and will change the reactivity of the wine towards the oxygen. For example, brining 1 ml/l oxygen in November won=t have the same effects as in June.
As an illustration, suppose that treatment is suspended temporarily because the temperature has dropped. One cannot simply double the dose of oxygen afterwards and expect the same effect.
4. Importance of CO2
CO2 delays the fining of the wine; among other things, by increasing its density. There is no problem in using the oxygenation technique in a wine with a high content of CO2. However, it is usually preferred to get rid of it before the operation, simply because to eliminate the CO2 in the wine during ageing would be a violent process that would adversely influence the aromas gained during that time.
5. Importance of SO2
Micro-oxygenation normally has no effect on SO2, as long as it is controlled. On the other hand, as soon as there is an accumulation of dissolved oxygen, there is a precipitation of the sulphur into sulphates, and the free SO2 drops. The raise of the temperature over 18oC seems to increase the consumption of the SO2 as well. Therefore, it is wise to check the free SO2 regularly.
6. Importance of an experimental control
Because micro-oxygenation is a new technology (a new knob to control an old parameter), the user should still consider it as an experiment. Therefore, everything should be carefully recorded: periods of time when used, temperature, racking, and so on. A control lot or an adequate number of samples of the same wine without micro-oxygenation should also be set aside, to be used as a comparison.
MICRO-OXYGENATION THROUGHOUT THE WINEMAKING PROCESS
1. During alcoholic fermentation
It is known that 4 ml/l of oxygen is needed at the peak of fermentation by the yeasts. The apparatus is capable of producing such a quantity of oxygen (when set on 120 m/l/month, that is to say 3.5 seconds for one day, at the peak; or, in two to four days, starting the second day of fermentation with a setting of 7 and 14 seconds).
For a red wine during maceration it is necessary to pierce a hole in the pomace with a PVC tube, in order to guide the diffuser into the wine. The tube stays in place so it is easy to remove at the end of the process.
2. During malolactic fermentation (MLF)
Among all the tanks observed while micro-oxygenation was occurring during the MLF, no negative effect has been noticed. There has been no particular increase of VA, nor have there been any taste problems. However, it is true that it=s a bit better to go through the MLF in barrels, which is a kind of oxygenation as well.
It seems desirable to delay the onset of MLF so that its action can be used to help consume aldehyde after pigment complexation is well accomplished.
Moreover, when the oxygenation starts right after the alcoholic fermentation, the stability of the color seems quite good. The low content of SO2 explains why some high quantities of oxygen brought in at that time will have big effects. A slight production of acetaldehyde just before the MLF explains the fixation of the color.
A controlled addition of oxygen may be recommended throughout the MLF. If the period of time during the MLF is long and without SO2, one must exercise caution.
3. Ageing of the red wines
As with any ageing regimen, a program must be conceived which incorporates the type of product desired, the time allowed for ageing and the bottling date.
The time required for the structuration phase varies according to the characteristics of the wine. During this phase the wine with micro-oxygenation may taste incorrect if the oxygenation is stopped before completion, and some reduction may appear. The wine must complete this period of time to get a correct balance back.
General guidelines include:
4. Evaluation of the need in oxygen according to the objective
Every wine has a different need for oxygen in order to express the best of its potential. Tasting is at present the only means to evaluate this need.
Two parameters are important:
The following two Tables depict seven classifications of need for oxygen:
Micro-Oxygenation Wine Types
Possible ranges for treatment regimen (mls/L/month)
When learning the technique, it may seem safest to try low levels first and see the result before increasing the dose. Actually, high levels for a short time early on when the wine can absorb them are a safer approach.
5. Some indicators to use
The measure of dissolved oxygen.
Vegetative aroma of the wine.
Micro-Oxygenation Questions and Answers
(An Ainterview@ compiled from e-mail conversation between Clark Smith of Vinovation and Thierry Lemaire of OenoDev.)
Clark: It is common practice in the U.S. to rack off gross lees promptly after alcoholic fermentation is complete (for example at pressing), but to allow contact of the wine on fine lees for two weeks in order to allow micronutrients helpful to ML bacteria to be evolved from yeasts. Then a second racking is done. Should the treatment commence at this point?
Thierry: The best time to start is when the AF is complete with or without lees, with or without cap. If we could deal with Brett, I=m almost sure that starting even before the end of AF would be interesting. We have to check that seriously.
Clark: If we commence while lees are present, will the turbulence caused by the gas be low enough that the lees will still settle so racking can still be done in two weeks?
Thierry: Yes. As long as the ceramic is not bubbling inside the lees, the movement is not strong enough to keep the solids in suspension. In many cases (especially stronger wines), the wine actually may settle faster.
Clark: Many wineries inoculate with Leuconostoc oenoes for ML during the primary fermentation. For this reason, ML may complete very promptly, even during the primary fermentation. In this case, do you wish for a period of micro-oxygenation to occur before SO2 is added? If so, how long should one wait to add SO2?
Thierry: We think that having very prompt ML is perhaps expedient for practical reasons and to feel comfortable that it is complete, but it doesn=t make any sense regarding the maturation aspects. However, if the ML occurs, it can be interesting to delay a little the sulfur addition, but it can result in other problems. In any case the idea is at least to bring fairly big amounts of O2 ASAP without O2 accumulation. This can be monitored by SO2 analysis, as it shouldn=t result in an unusual depletion.
Clark: If one Aguesses@ the correct amount of O2 to add, are there other ways to tell that too much O2 is being used, which are useful prior to completion of ML?
Thierry: Prior completion of ML, we still don=t know what Atoo much@ means. What we can say is that there=s no need to accumulate tremendous amounts of aldehyde, to the extent that it results in remaining aldehyde after ML, which doesn=t seem to be a good idea.
Clark: From some old literature on microbullage we were given by Bill Dyer, we got a chart proposing treatments 0.5 to 2.5 ml/L/mo from A - E based in degree of dilution and vegetative character. This seems like a useful document to work from in developing an English language guide. Do you like this approach?
Thierry: The levels to start in red wines much be much more than 0.5 to 2.5 ml/l/mo. If it=s prior to ML, the starting point would be 10 minimum for a weak wine and 60 or more for a strong dark extract. The level has to be then adjusted in function of aldehyde perception. Measurement would be helpful but it=s not very easy to conduct because it=s not very stable. If should be measured in tank.
Clark: I=m confused. Is the 10 - 60 ml/L/mo recommendation only for before SO2 is added (you keep saying Apre ML@, but I think you mean Apre SO2" n=est-ce pas?). What is desirable aldehyde perception? Faintly evident, not strong? If they measure it, what is a good level? What do you mean by measurement in tank - headspace GC?
Thierry: The chart is OK as a model. The doses are old fashioned. It has not a lot of sense to speak of dose like that without specifying precisely when it=s delivered. I would widen the range after ML from 0.5 to 10 ml/l/mo. 10 to 60 is OK prior to ML.
I keep saying ML (but it may change one day) because, due to the CO2 production (maybe) or due to a metabolism of the bacteria (maybe) the ML is a very effective period for consuming the extra aldehyde. It=s safer to play (to Asurf@) the aldehyde before ML than later.
At this stage of our understanding, the desirable aldehyde perception to maintain is so far more related to the winemaker=s personal degree of concern than the actual wine=s need. It=s really important to find a way of measuring the aldehyde production and the aldehyde consumption ability and to put figures behind it. So far, our position is rather simplistic: if we can slightly find it, that means that there=s some available for further reactions. Some people go further and the wine is really aldehydic. The last thing I have to add is that we never had any bad experience of having even a lot of aldehyde in the early age of the wine. Later, it=s another question.
Clark: What is the best cellar temperature for the treatment? If this cannot be controlled, what are your recommendations?
Thierry: The best range is between 59 and 650F (after ML). If it cannot be controlled, then it=s safe to keep the level of oxygenation under the curve we presented. If you don=t have it, I=ll send it as a file (ppt).
Clark: Many people are asking for scientific papers to read concerning this technique. Can you give us some good references?
Thierry: That=s a problematic question because the only >scientific= papers we have are from INRA and are quite old (>95). There=s a bunch of articles treating of Microx which are all practical and not scientific. We are planning for the next vintage to set some simple and precise protocols for writing something. Michel MOUTOUNET will be our consultant. We will set a trial for Australian Magazine in Languedoc and Spain. There=s a trial going on at ASTI. And hopefully, we=ll do something with DAVIS, FRESNO, etc?....
Clark: Most California wine is sent to barrels, and we are at this stage promoting this technique as a preconditioning prior to barreling down. Is it reasonable to say that once the harmonization phase has begun (the wine begins to soften) that this is a good time to barrel?
Thierry: No. The good time to barrel can be much earlier than the harmonization. It=s difficult to answer precisely because it could be the subject of a specific trial. The most important thing is to stabilize as many free anthocyanins as possible at the beginning. Then the further constructions may occur slowly (structuration phase) which can take place in barrels.
Clark: Will August vacation be a problem for supply?
Thierry: August vacations shouldn=t be a problem because we don=t close nor do our suppliers either. The stocks of parts have been felt before. However, the problem might be an acceleration of orders. I=m particularly concerned by some last minute orders in Italy.
Clark: What advice do you have on the correct grade of O2? Can we use welding grade, or must it be hospital grade?
Thierry: In France we can find Food Grade oxygen. I guess it exists in the USA. If not, hospital should be reasonable. It=s actually the same gas. Only the protocol of cylinder conditioning (rinsing, filtering...) is different.
Clark: Is there an influence of pH on the treatment?
Thierry: The pH is certainly important in the oxidation reactions. The higher the pH, the more phenolate form you find versus phenol. It results in a stronger reactivity of the phenols to give semi quinonic radicals. However there=s no direct consequence in the way we apply microx. The only thing is that the higher is the pH, the more careful we will be, especially regarding the Brettanomyces problems.
Home | WineQuality Enhancement | The State-of-the-Art Estate Winery | Services at our Facility | Winemaking Fundamentals | CostSavings | Vineyard Enology | International Services | About Us | Contact Us | International Links