Les Differents Roles De L'oxygene

DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN, 1

THE DIVERSE FUNCTIONS OF OXYGEN – FIRST PART

Dominique DELTEIL. Scientific Director, ICV1

¾ To stabilize and develop the taste and aroma of ripe berries. ¾ To control a complete and smooth alcoholic fermentation. ¾ To limit the occurrence of sulphur aromas (odours of garlic, onion, rubber, tin can, etc.) These are three key objectives of a well devised and properly realized Mediterranean vinification. Oxygen plays a direct role in each one of these objectives. Sometimes positively, and sometimes negatively. Some practical facts in order to prevent certain winemaking mistakes: ¾ Oxygen is soluble in must and wine. It is always present in the air, which surrounds the tanks, the pipes, the connections between pipes, the presses. Oxygen is always more concentrated in the air than in must and tank filled wines: Therefore, it will always tend to dissolve therein. This is also true for a carbon dioxide saturated must during vigorous alcoholic fermentation. This dissolution is extremely fast: the must in the receiving trays of a pneumatic press is already completely saturated with oxygen. Oxygen always abounds in winery air, even when the latter is enriched witch carbon dioxide. ¾ An air or oxygen bubble, which bursts on the surface of must or wine means gas, which escapes from the liquid: this bubble has transferred little or no oxygen to the liquid. The colder musts and wines are, the more oxygen they can dissolve: up to approximately 10 mg/l. ¾ When must and wine are in movement and in thin layers, the oxygen dissolution is faster. It is a voluntary Venturi effect when a stainless steel coupler with a frit is used or when the pipe couplers are slightly loosened. It is an involuntary Venturi effect when the valve of a pump is worn or when the thread of pipe couplers is damaged. Whether voluntary or involuntary, the result is the same. An open stream of wine, which sprays into a tub during pumping over, dissolves oxygen quite well, and even more if the drop is considerable. For about ten years, the ICV has studied different techniques for oxygen protection, or, on the contrary, techniques for oxygen addition under Mediterranean conditions. These techniques are reviewed below.

Protecting the grapes and musts during the pre-fermentation stages The Mediterranean grapes have characteristics, which render them particularly sensitive towards oxidation reactions and browning. These characteristics are the increased cellular maturity of the pulp, with a high concentration of oxidisable phenolic acids and high pH values. Until the onset of fermentation, these musts and grapes have to be protected against oxidation. Oxygen does not react directly with SO2. Thus, SO2 does not influence the dissolution of oxygen in the must. SO2 is effective since, from the beginning, it prevents the chain reactions, which create brown compounds and destroy the majority of varietal aromas. It is an error to believe that any contact of grapes and musts with air could be avoided in the winery. However, homogenous and successive sulphite additions to the must have to constantly ensure a minimal and efficient presence of SO2. This is called the “internal” protection of the must. In case of mechanical harvest, this protection has to begin in the receiving bin of the harvester. The addition of CO2 to the grapes and the must, and the covering of the must by CO2 are effective complements to SO2: they make SO2 more efficient by limiting the contact with air. This is the “external” protection. It can not replace the internal protection, but completes it.

Supplying oxygen to yeasts JM Sablayrolles of INRA in Montpellier has shown that oxygen added to fermenting must was used by yeasts, and that different enological yeasts could have varying needs. Added at 14.8°Brix, the oxygen assists yeasts to produce survival factors, and thus, better resist the difficult conditions present at the end of fermentation. Since 1991, ICV has integrated this oxygen addition in its fermentation recommendations. Looking back, it can be said that this is a key factor for ensuring a smooth and complete fermentation. This is true for both white and red wines. The optimum quantity is between 5 and 10 mg/l. The technical solutions: pumping over the entire must with a fritted stainless steel coupler, a precise injection of pure oxygen with a diffuser, or pumping over the entire must after spraying into an open tub. The last solution, often not quite as effective, requires two additions: either on the same day, or a pumping over on two successive days. Stirring up the tank content with an aeration pipe does not add enough oxygen. The pipe produces big bubbles intended to stir up the liquid. The re-suspension of yeast is always interesting at this stage, but the yeast won’t produce survival factors. In white and rosé winemaking, this addition is not in contradiction to the pre-fermentation protection from oxygen, if applied at the right time. Fully fermenting yeast would consume the oxygen added almost instantly. Thus, it would not participate in oxidative reactions, even if no active SO2 were left in the fermenting must. The fragile varietal aromas are perfectly preserved, and even better expressed, since oxygen additions limit unpleasant sulphur aromas. These oxygen additions are all the more necessary for the yeast given that the other fermentation parameters are difficult. Amongst these parameters, some are typical for white and red Mediterranean musts: low yeast available nitrogen and high sugar concentrations. Others are due to the technology: highly clarified musts without addition of fine sediments, low temperatures, no yeast stirring at the tank bottom. After the 1994 vintage, the ICV has emphasized the advantages of an additional and earlier oxygenation, at around 19.4°Brix. In highly clarified musts with high sugar concentrations (over 13% potential alcohol), which are fermented under 17°C, this oxygenation helps to reduce the risk of volatile acidity development with certain yeasts.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N. 4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN, 3 Oxygen addition during alcoholic maceration in red winemaking

In red winemaking, yeast have particularly high oxygen requirements. The must conditions are difficult: low nitrogen content and high sugar concentrations. Temperature peaks above 28°C strongly affect yeast survival and the completion of the fermentation. This is true no matter when the temperature peak occurs.

During maceration, oxygen also participates in complex reactions. It contributes to colour stabilization and chemical modifications of tannins. These modifications generate more stable and also rounder tannins. Must aeration during maceration reduces the development of malodorous sulphur compounds. These compounds also cause bitterness and aggressive tannins. In order to control the colour quality, the tannins, and the purity of the grape aromas, it is necessary to establish the correct extent and schedule of aerations. Please refer to the experimental results, below. There are different methods available for aeration of a red wine tank during maceration: pumping over the entire must volume with an open tub, pure oxygen injection into the tank under the cap, or complete delestage of the entire tank. The latter would be accompanied either by injection of pure oxygen to the separated liquid phase, drainage (by spraying) of the entire tank into an open tub, or by pumping the must back into the tank using a fritted stainless steel coupler. Cap punching (“pigeage”, mechanical cap submersion) is a good method for maceration, but it does not oxygenate the must during the fermentation.

In the case of vintages rich in tannins, with rather thick and hard skins, these tannins would thus have to be stabilized and smoothened during maceration in order to avoid gustative harshness. This harshness is commonly encountered with such skins.

A customized aeration program starts early on, that is, as soon as the cap has formed. For macerations shorter than 6 days, it is advisable to aerate every day. For long macerations, it is suitable to aerate every day during the active phase of fermentation. Afterwards, the schedule has to be adapted according to the results of tastings. With Botrytis affected grapes, it is desirable to macerate only briefly (2 to 3 days) with concurrent aerations. These aerations finish upon devatting and as long as the laccase remains active: negative browning test of the wine. As long as the aerations take place during macerations which do not exceed 4 days, there are only positive effects: more vivid and stable colour, less earthy or mouldy odours.

Protecting white and rosé wines after fermentation.

Regular oxygen additions to red wines during ageing. In the second part of “The diverse functions of oxygen”, which will be published shortly.

An experimental demonstration The Syrah harvest was distributed evenly in two identical vats. ¾ Vinification protocol: Destemming – crushing – addition of selected enzymes (1 g/hl) – sulphiting (5 g/hl) – yeast addition (20 g/hl, strain ICV-GRE) – maximum temperature 28°C – cap punching once daily – devatting 6 days after cap formation, and thus, after 6 cap punchings – drainage and pressing, blending first pressings – aerated racking 24 h after devatting – second aerated racking, 48 hours after the first racking – direct inoculation of selected lactic acid bacteria – aerated racking 24 hours after completion of malolactic fermentation – sulphiting (3 g/hl). Bottling in December.

The first tank was oxygenated 5 times on the day it reached 14.8°Brix. Each addition occurred by injection of 10 mg/l. VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N. 4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN, 4

The second tank was oxygenated once every day for 5 days by injection of 10 mg/l.

5 oxygenations on one day 5 oxygenations during 5 days

51.5 50 48.7 48.1 46.2 46.1 34.2 35.8 Relative scale

0 End of AF End of MLF After 4 months After 4 years

Study carried out by the R&D department of the ICV Jointly financed by ICV, ONIVINS, Conseil Régional Rhône Alpes within the framework of the state/regional contract plan, enological experimentation Figure 1: Effect of the aeration schedule on polyphenols in red Syrah wine.

5 oxygenations on one day 5 oxygenations during 5 days e

3 s scal ysi

2 y anal

ASDQ ICV 1 ve sensor ti a l e

R 0 Herbaceous Jam Volume Tannic intensity Bitterness

Figure 2: Effect of the aeration schedule on the sensory profile of red Syrah wine after 4 years bottle ageing.

Comments The two tanks received exactly the same overall oxygen quantity. In this vinification, the mature grapes, the shape of the tank and the cap punching operations have optimized the diffusion of stable colour and tannins. The regular distribution of oxygen additions led to a better stability of the polyphenols compared with carrying out the additions on one single day, as shown by the measurements realized over time in Figure 1. After 4 years, this increased chemical stability translates into significant sensory differences: Figure 2. The wine produced by regular oxygen additions during maceration is fruity and intense, with smooth tannins: strong aromas of red fruit jam, big volume, strong tannic intensity without bitterness. This is the typical profile of a commercially well-positioned red wine in the mid range. The wine produced with a concentrated addition of oxygen displays a less Mediterranean profile, with vegetal characters and appears more diluted and aggressive in the mouth.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N. 4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN. 2ND PART, 1

THE DIVERSE FUNCTIONS OF OXYGEN – 2ND PART

Dominique DELTEIL. Scientific Director ICV1

Protecting white and rosé wines from the last quarter of the alcoholic fermentation onwards

White musts and wines from the Mediterranean are very susceptible to pinking, particularly the 1998, 1999 and 2000 vintages. The pinking is attributable to oxidation of small polyphenols of white grapes. These small polyphenols are naturally colourless. They are soluble in the must and later the wine. When properly protected, they remain colourless during the entire process. The best prevention is to avoid their participation in oxidative reactions and thus, their colourisation.

• The continuous external protection of the fermenting must by CO2 is the first preventive action.

Yeast continuously produce large amounts of CO2 during active fermentations. Caution is required from the last quarter of the alcoholic fermentation (from 7.6° - 5.1°Brix) onwards. The headspace above the must has to be saturated with CO2. In the case of clarified musts, which are rich in sugars and fermented at low temperatures, the risks of a sluggish end of fermentation are high, and so are the risks of pinking. In order to assess the risk after reaching 5.1°Brix, a 0.25 litre sample is introduced into a flint bottle. When the risk is high, the sample will change colour within hours compared with the must in the tank. In such a situation, the external protection of the must has to be more carefully supervised as long as the fermentation continues. Sulphiting must with fermenting yeast would be a serious mistake. At this stage, it is completely inefficient to prevent pinking. Also, the yeast will react by producing acetaldehyde and other SO2-binding compounds. When colourless, the small polyphenols responsible for pinking are virtually unaffected by bentonite or casein finings. A must, which was treated with these compounds during clarification or fermentation, remains susceptible to pinking. By way of contrast, preventive treatment of fermenting must with PVPP is the only efficient way to complete the protection against oxidation. Note: In view of the hygienic regulations, please remember to ask the distributor to provide a certificate of conformity with the current regulations, notably the RCEE 1622/2000.

The internal protection of the wine has to be initiated as soon as the alcoholic fermentation is complete. This is valid when the malolactic fermentation is undesired. • The first protective sulphite addition is carried out in the fermentation tank, as soon as the sugars are depleted.

The addition has to be sufficient in order for some free SO2 to remain during several weeks. For this initial sulphiting, between 5 and 7 g/hl of SO2 are added considering the usual pH values of Mediterranean wines, but the exact addition has to be adjusted depending on the other analytical parameters.

1 Institut Coopératif du Vin, la Jasse de Maurin, 34970 LATTES, France E-mail : [email protected] : internet home page: http://www.icv.fr VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N°4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN. 2ND PART, 2 The addition of ascorbic acid can complete the efficiency of SO2 for certain wines. When all the other parameters have been adequately considered, a 5 g/hl addition will perfectly serve its purpose.

• The homogenous sulphite addition is a key parameter of winemaking.

• It is crucial to achieve the desired SO2 concentration in the entire tank, particularly in the yeast sediment at the tank bottom. • Afterwards, white wines have to be racked off within 24 h following sulphite addition, while completely avoiding contact with air. Before the wine is pumped, the pipes and the bottom (up to 1 meter height) of the receiving tank should be saturated with CO2, the pump valves should be in good condition and the pipefittings undamaged. The wine should remain under the CO2 blanket during the pumping. Numerous studies have shown that sulphite addition to wines in the fermentation tank led to the production of unpleasant sulphur odours (rotten egg, onion, garlic, etc.). This is the case when the wine is left unstirred on the yeast lees for several days.

For Mediterranean white and rosé wines, sulphite addition to the fermentation tank upon sugar depletion, and 24 hours before racking allows to: • implement an efficient internal protection during a stage which is very prone to involuntary Venturi effects: the racking • avoid the production of unpleasant sulphur odours by stirring the yeast twice: once during sulphite addition, and the second time during racking (for those, which have not sedimented).

For rosé wines, the reasons for oxidations during slow final stages of fermentations or during rackings are the same. However, the consequences are different: a loss of the vivid rose hues results, with appearance of more yellowish tones. The preventive measures are the same as for white wines.

Regular addition of oxygen to red wines during ageing: • Before and after malolactic fermentation

As soon as the wine has been devatted, 5 factors have to be considered together for the further procedure since they strongly interfere with each other. It is not possible to consider only one of these factors without taking into account the others. 1. The wine polyphenol and polysaccharide composition, and the nature of the cap management 2. The wine yeast lees: their quantity but also their composition 3. Wine and yeast lees stirrings 4. The oak, when barrel ageing is carried out, and obviously 5. The oxygen

How can all these factors be managed and a practical line of action be defined for any wine type? Certain procedures have organizational priority, notably the rackings. Racking leads to oxygen additions and stirring of yeast. When the racking program is planned, its impacts on other factors are assessed: oxygen and yeast stirring. Afterwards, a further addition can be envisaged, if the oxygen contribution through racking was not sufficient, or if the yeast were not sufficiently stirred.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N°4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN. 2ND PART, 3

Two examples:

Example 1. A wine whose alcoholic fermentation finished during maceration. Devatting, pressing, and blending of the free-run and first pressings. Completion of two rackings (24 hours and 72 after devatting) with aeration. Afterwards, inoculation with lactic acid bacteria in order to complete malolactic fermentation within 10 to 15 days after devatting. Comments: Since the wine takes up oxygen during the pumpings, dissolved oxygen is supplied twice in the 3 days following devatting. At this stage of the vinification, this practice is consistent with the elimination of large grape particles from the wine, the yeast residue, and the objective of avoiding vegetal aromas and sulphur odours. Normally, there is no need for further oxygen additions. In wineries where such rackings are easier to perform in closed systems, 2 mg/l of oxygen have to be dissolved in the receiving tank instead, for example with a diffuser. Afterwards, the fast implementation of the malolactic fermentation will maintain the yeast in solution thanks to the CO2 produced by the bacteria. Because of the oxygen additions made during maceration (compare first part), and then during the pre-MLF rackings, the wine polyphenolic system (polyphenols and polysaccharides) will be in such a state that it will continue its positive evolution during the 8 to 10 days of MLF at 20°C. The bacterial polysaccharides will also positively participate in the evolution of the system. After malic acid depletion, a racking followed by a homogenous sulphite addition will establish appropriate microbiological stability and allow promoting the aromatic and gustative development of the wine. Microoxygenation of the wine can be initiated at the time of inoculation with lactic acid bacteria for certain wines with very high polyphenol concentrations. For these wines, the regular stirring of the residual yeast cells (particularly with an immersed food grade pump) will allow to develop the polyphenol and polysaccharide system even better during MLF.

Example 2. A short maceration (5 days at 26°C). Devatting, pressing, and blending of the free-run juice and first pressings at 5.1°Brix. One aerated racking 24 hours after devatting. Completion of alcoholic fermentation at 24°C. Inoculation with lactic acid bacteria to complete MLF within two weeks following devatting.

Comments: The two aerations caused by the devatting and the first racking have stirred up the yeasts and contributed dissolved oxygen twice; the grape sediments have equally been removed. However, during the 5 to 6 days required to complete alcoholic fermentation after devatting, the must does not receive additional oxygen. Thus, it is necessary to add 2 mg/l of oxygen daily, for example with a diffuser. If the diffuser is placed at the bottom of the tank, the addition will also positively contribute to yeast stirring. As soon as the fermentation is complete, the wine is racked with aeration. 48 hours after this racking step, the wine is racked again and inoculated with lactic acid bacteria. If these rackings are easier to perform with closed systems, approximately 2 mg/l of oxygen have to be added to the receiving tank every time, for example with a diffuser. Such as the wine in example 1, this wine will progress in its positive aromatic and gustative evolution during the fast MLF, without oxygen additions or stirrings generally being necessary.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N°4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN. 2ND PART, 4 After the depletion of malic acid, the wine is racked and sulphite is added for the same reasons as given in example 1.

• After the malolactic fermentation From this moment onwards, the wines have a fairly low particle load. In fact, the very first racking after devatting has removed all grape sediments. The following 2 rackings both remove part of the yeasts. The post-MLF racking removes very few lactic acid bacteria because lactic acid bacteria sediment very poorly, but they constitute only a very small mass.

The wine always requires oxygen to proceed in the development of the polyphenolic and polysaccharide system. But the oxygen should not be added at similar amounts as during the previous stages.

Microoxygenation is an interesting tool for the purpose of adding small oxygen quantities regularly: Please refer to the experimental results, below. The constraints and limitations of its utilization in Mediterranean red winemaking are now widely known: Dosage, height of the liquid column in the tank, temperature. Wines, which still contain significant amounts of yeast, have to be stirred regularly by other means (specifically an immersed pump). During microoxygenation, the wine is developed homogeneously. But yeast are too heavy to be kept in solution through the weak flow caused by the microoxygenation. During tank ageing, the regular stirring of the wine (especially with an agitator or an immersed pump) also allows to develop wines favourably, specifically those, which were well supplied with oxygen during maceration and before MLF.

In barrels, the method of reference is the batonnage (yeast less stirring).

The schedule is to be adapted according to the moment of barrel filling, and thus the quantity of yeasts still in suspension, the polyphenolic and polysaccharide structure of the wine, the age and quality of the barrels, and the desired integration of wine and oak. An interesting result may serve as example: New barrels, a perfectly matured Syrah produced by long maceration, barrelled 24 hours after draining and pressing (with all the yeast from the alcoholic fermentation but without grape particles), barrel MLF, post-MLF sulphite addition, batonnage (yeast lees stirring) once per week during 6 months, then batonnage twice monthly for another 6 months, with no rackings during the 12 months. While certainly requiring a high workload and a special arrangement in the cellar (barrels limited to one level), in the end, an individual Mediterranean wine is obtained. In this example, the 5 factors cited above (wine, yeast, oak, stirring, oxygen) have been combined in a particular way, while remaining consistent with certain market objectives.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N°4 DELTEIL, THE DIVERSE FUNCTIONS OF OXYGEN. 2ND PART, 5 An experimental demonstration Corbières 1993 Study. This initial study on microoxygenation performed by the ICV under winery conditions was carried out with a red Corbières wine (Carignan, Grenache, Syrah). The wine was equally distributed into two identical tanks and held at the same temperature (16°C). A 5 ml/l/month addition of oxygen was chosen for the microoxygenation treatment. After 3 months the wines were sampled and analysed.

Q 2 Control tank Microoxygenated tank

1.5

1 ICV y analysis scale ASD 0.5

lative sensor Red fruit Candied Fruit Prunes Liquorice Pepper Animal e R

Figure 1: Effect of microoxygenation on the aroma profile. Corbières 1993

2.5 Control tank Microoxygenated tank

1.5

1 ASDQ ICV 0.5

0 Relative sensory analysis scale Volume Acidity Tannic Intensity Astringency Bitterness

Figure 2: Effect of microoxygenation on gustative profile. Corbières 1993

Experiments carried out by the ICV R&D department. Results published in “La Vigne”, n°53, 1995 Comments The base wine had neither aromatic nor gustative faults. Microoxygenation allowed developing a more mature and concentrated aroma profile: candied fruit, liquorice and pepper. During these 3 months, without stirring or aeration, the control wine developed aromas reminiscent of a fast evolution, even over-ageing (“prune” descriptor dominant), and at the same time “reduced” aromas (“animal” descriptor). Please note that in the case of this wine, the predominant “animal” character is attributable to a lack of aroma expression and not to the development of Brettanomyces yeast. In the mouth, the microoxygenated wine has more volume and tannic strength, with tannins of better quality: “astringency” and “bitterness” were lower. During this initial study in 1993, it was demonstrated that microoxygenation is an efficient and practical method to manage Mediterranean red wines.

VINIDEA.NET, WINE INTERNET TECHNICAL JOURNAL, 2004, N°4