Oxygen is the enemy of wine. This is well understood. Leave the cork out of a bottle, or the bung out of a barrel, for long enough and even the most stalwart wine will sour and decay.
And yet oxygen exposure during fermentation and élevage is essential to produce a stable and long-lasting wine. This is especially true for red wines, where its presence can help elongate tannins (which renders them more texturally smooth) and stabilize color, among other things. But as with ancient King Mithridates, who regularly consumed small amounts of poison to become immune to its fatal effects, wine must be fed oxygen in carefully controlled doses, lest the cure become the cancer.
There are several ways to introduce oxygen to a fermenting or aging wine, and some of the more common methods are defined below. But first we must define oxidation, as it is a term with two meanings. In the wine industry, we think of oxidation as a flaw; a wine is “oxidized” when it tastes tired, either through faulty handling or old age. Sometimes, wines are deliberately oxidized, such as with Tawny Port or certain types of Sherry, but in general it is a quality to be avoided. Yet from a chemical perspective, oxidation is simply one half of a “redox” reaction (the other half being reduction), wherein electrons are exchanged in the production of stable molecular bonds. A compound or element is “oxidized” when it donates electrons to a bond, and is “reduced” when it gains electrons. Oxygen doesn’t actually need to be present for this to occur, but oxygen ions are by far the most famous oxidizers, as they need to donate two electrons to become stable (hence the reason they bond with two hydrogen ions to form water).
Pumping over and punching down are the two primary ways to keep caps wet, circulate wine, and introduce oxygen during red wine fermentation. Pumpovers occur when a wine is pumped from the bottom of a tank to the top. This can be done anaerobically (i.e., within a closed tank) or aerobically, with the wine shot through the air onto the cap as if through a firehose. Punching down, also known as pigéage, is the manual submersion of the cap beneath the surface of the wine. This can be done using a plunger or the human body, or via automation.
Each approach has its attributes, and both have their nuances. Pumpovers are helpful in that they can circulate the entire volume of a tank, which will evenly disperse the yeast and make for a uniform temperature distribution. Punchdowns are rarely as thorough, and can range from gentle to violent (i.e., with splashing), which affects the amount of oxygen exposure and the level of color and tannin extraction.
Délestage happens when the juice in a fermenting or macerating tank is drained completely off its skins, and then added back in. It can be thought of as a more dramatic pumpover.
Micro-oxygenation refers to the steady addition of small amounts of oxygen into a tank of wine. This is generally administered via a type of IV, which runs from an oxygen tank to a porous plate placed at the bottom of a tank.
The most common, and most important, method of oxygen addition to red wine is barrel aging. Oxygen is introduced slowly to the wine through the oak’s pores and bung. The amount of oxygen depends on the type and age of the oak, with new oak boasting larger, less clogged pores and therefore offering the greatest oxygen exchange. French oak is also more porous than American, as American oak’s thicker grain makes for a denser, less porous barrel.
A red wine is racked when it is drained from a barrel and placed into either another barrel or a tank. The purpose of racking is often to remove a wine from its gross lees (a heavy sediment composed of yeast cells, protein, and particulate grape matter that remains after fermentation), but often a wine is racked simply to introduce oxygen. This is commonly employed if a barrel starts to exhibit reductive aromas. Careful racking is also often used by those who don’t want to fine or filter their wine.
For this article, I interviewed five winemakers on their approaches to oxygen during red wine making. These winemakers are Louis Barruol of Château de Sainte Cosme in Gigondas and Forge Cellars in the Finger Lakes, Thomas Savre of Lingua Franca in Oregon, Yiannis Paraskevopoulos of Gaia Wines in Nemea and Santorini, Christian Sepúlveda of Bouchon Family Wines in Chile’s Maule Valley, and Carlos López de Lacalle from Artadi in Rioja and Alicante.
Clockwise from top left: Carlos López de Lacalle, Thomas Savre, Louis Barruol, Yiannis Paraskevopoulos, and Christian Sepúlveda.
Kelli White: What are your thoughts on punching down versus pumping over?
Louis Barruol: It depends on the wine, terroir, level of ripening, and whether we destemmed or not. It is always difficult to judge a technique out of a system. But let’s say that pumping over is a softer technique than punching down. But this is a very general statement.
Thomas Savre: Punching down and pumping over will have different consequences and impact on the extraction. Pumping over is more gentle on the grapes; I like to do different types of pumpovers, with air or no air depending on where we are in the fermentation. Toward the end of the fermentation, we use a few punchdowns for several reasons. At this time, we would assess the level of extraction by taste and choose between doing a gentle extraction, such as a pumpover, or a light punchdown. Punching down will allow us to release the sugar trapped in the intact berries and will give fermentation a natural temperature boost.
Yiannis Paraskevopoulos: I prefer pumping over to punching down when I’m aiming to produce a fruity red with low concentration in structural tannins—a red for a rather rapid consumption, if you will. I also avoid punching down when a proportion of berries are not crushed. It works the other way around when a long-aging-potential red is the goal.
Christian Sepúlveda: Punching down is good because you don’t use pumps, and it’s supposed to be a soft extraction, but I think you extract a lot. It also depends if you are doing manual or mechanical punchdowns. The problem for me is that you can’t get as much oxygen in the fermentation as with a pumpover, and the wine needs to be in an open tank. Pumping over is more used because it can take place in an open or a closed tank, and it can be aggressive or soft. In general, I think it’s more versatile.
Carlos López de Lacalle: We do short punchdowns with our feet to get a light extraction, and we use pumpovers to control the temperature. These are of a very short time, maximum 15 minutes.
KW: Does your approach change for different varieties? Why or why not?
YP: Well, yes. Take the example of a Syrah. Although the desired result is a red wine with a long aging potential, punching down would be a poor choice because of the bitterness that would result. In this case, a combination of pumping over with délestage (while softly breaking and rearranging the cap with rods) seems to be my weapon of choice. In addition to Syrah, I avoid punching down on varieties that have a thin skin, because doing so would lead to the production of a great amount of debris. Clarification of the young wine would then be challenging.
CS: In general, I use punchdowns for Pinot Noir and some País in open tanks. For the rest, I pump over. In the case of Pinot Noir and País, I don’t pump over because they are sensitive to over-extraction. In general, my approach varies more by soil than variety. For example, with granitic soil, I only make one short, anaerobic pumpover per day, but when the wine reaches a density of 1070° (17.66 Brix), I change to one aerobic pumpover a day. With clay soil, I make two pumpovers of one-quarter of the volume of the tank each time. My approach also depends on the year. In 2017, the tannins were a little bit more rough, versus 2018 that, for me, has more soft tannins.
CL: We do not really change our approach depending the different varieties, but we do vary timings and amount of pumpovers or punchdowns. For example, Tempranillo has a better resistance to oxidation and has thicker skins than Garnacha, so we can do maybe one or two more punchdowns per day.
KW: Does your approach change according to the stage of fermentation? Why or why not?
LB: Yes. Yeast needs a lot of oxygen at around 1060 density (15.48 Brix), [about one-third of the way through fermentation], to multiply.
TS: In the juice phase, we only pump over, with no air to protect from any oxidation. When fermentation starts, we like to introduce more air to help the yeast develop. At mid-fermentation, we gently pump over and adjust depending on the level of whole cluster. Finally, at the end of fermentation, around 0 Brix, I like to do [a] few punchdowns, and this will dictate our extraction level.
YP: As a general rule, we pump over near the beginning of the fermentation, which enhances fruit expression, and punch down toward the end of the fermentation, which promotes extraction of structural tannins. Also, if the potential ABV is expected to be higher than 14%, late pumping over can lead to high losses of alcohol and fruit character.
CS: Yes, at the beginning, I extract more than [at] the end, so the idea is not to introduce oxygen early on. In the beginning, I use punchdowns or anaerobic pumpovers, and when the yeast is fully developed (in terms of population), I start to make aerobic pumpovers. The thinking here is that the oxygen will help the yeast finish fermentation and help to start to make tannin-anthocyanin bridges with ethanol (oxidation of the alcohol), so you get more stable color. Tannins will also polymerize. Oxygen helps the short chains of tannin become larger and therefore softer.
CL: Yes, we use slightly longer pumpovers when the momentum of the fermentation is at its peak, as it generates more temperature, then we go shorter.
KW: Does your approach change according to the ripeness of the grapes? Why or why not?
LB: Yes. Manipulating unripe grapes is dangerous. You can get green characters.
YP: Indirectly. Low ripeness and punching down makes no sense, because the tannins are still green and harsh, thus a technique that would boost their extraction doesn’t sound right. The wines that would result would be aggressive and would remain as such over time. Strangely enough, punching down doesn’t work on overripe grapes either. Over-ripening makes skins more brittle, which would totally “decompose” to a muddy deposit. Not a good idea either. In short, go punching down when ripeness is just right!
CS: Yes. In general, with green or unripe fruit I try to extract the least that I can, wetting the cap once a day.
CL: Not really, but we tend to do fewer punchdowns with the feet when the maturity is not at its peak.
KW: How do you feel about automated versus manual punchdowns?
LB: If you use automated punchdowns, you don’t really feel anything and you don’t really know what you do. I prefer manual.
TS: Automated puncheons are very efficient and do a great job, but to me, as I am learning more and more about our vineyards and site, I want to have a feel for the fruit in the tanks. So we do manual punchdowns, and if we feel like it, I even prefer to do foot stomping.
YP: What a question! I fail to see the advantage of a manual punchdown over an automated one (unless you enjoy terrorizing your employees or because a gym isn’t nearby), but even if I did, the size of the fermenter and subsequently the size of the cap is a limiting factor. Try to punch down manually—in an effective way, that is—the cap on a 100-hectoliter fermenter and then we can discuss advantages!
CL: We prefer to use manual punchdowns with the feet. They allow you to feel the cap and see how far you can go or not.
KW: Does your choice of fermentation vessel (open or closed top; made of steel, wood, clay, concrete, or plastic) have anything to do with managing oxidation or reduction? If so, how does this vary by variety?
LB: Yes, it does since those materials are all different and they leave different levels of dissolved oxygen.
TS: At Lingua Franca, we only work with Pinot Noir. We work with stainless steel open-top tanks of different sizes, and also concrete. This is the first year I am using our concrete tanks for Lingua Franca, and we are still trying to understand the impact of each of the vessels on the wines. But I can tell you there are some significant differences. We [saw] on our yearly post-malolactic tasting [in early March] with Dominique Lafon and Larry Stone that we have excellent results with both types. Interestingly, I found less reduction with concrete than with steel. People think that concrete is porous, but [it] is not. There is a slight release of oxygen due to a chemical reaction between tartaric acid in the wine and concrete paste.
YP: Open versus closed fermenters is the first [question], where the material of choice is the second one. Obviously, both questions have a common ground, which is the huge subject of oxygen management. I’m afraid that in many cases, marketing was the answer to the choice of the fermenter (those wooden or clay ones look so sexy…!).
Oxygen can be a friend or a foe, depending on how well one manages it. In any case, you have to manage it. Open fermenters are a no, a straight and unconditional no, unless you are into Vegas fun. Gambling isn’t my style. Open fermenters allow no oxygen management, are an open gate to any microorganism passing by, lead to aroma and alcohol losses, [and] do not allow long post-fermentation extractions—unless vinegar is your final destination. But open fermenters are “old style,” thus romantic, thus traditional, thus of higher marketing value!
As far as material goes, put aside the sexiness of wood, clay, and concrete, and ask yourself three questions. One, how much oxygen [do] you need during fermentation, and at which moment? Two, do you need a rapid uptake of ellagitannins? Three, how does temperature inertia affect your fermenting must? My approach is simple. Wooden tanks work great with varieties that have an anthocyanin richness and a tannin deficit, i.e., a case in which you need a rapid formation of tannin-anthocyanin complexes, and with varieties that have a predisposition for reductiveness, such as Syrah. Stainless steel allows you total control on the amounts of oxygen that you choose to add to your fermenting must and to this extent are the ideal vessels, particularly if you simultaneously run alcoholic and malolactic fermentations. Clay and concrete are somewhere in between as far as oxygen uptake goes, but offer a better temperature inertia, if that interests you for a strange reason at this point of the process. The bottom line is that being able to answer those three question is the key for choosing your fermenter.
CS: For reds in general, I prefer concrete, because I get less reduction and the tannins finish softer. Last year, I fermented the same variety (picked the same day) in both concrete and steel, and with the steel, the tannins were a little bit rough, and there was also more reduction. During the last stages of fermentation (when the yeast is not producing a lot of heat), concrete does a better job of retaining that heat. In steel, you can lose that heat very easily.
CL: Not really. We always work with grapes that are sensitive to oxidation, so the use of steel tanks does not affect us as much as with grapes such as Syrah. Regarding open versus closed, as we do manual punchdowns, we always use open tanks.
KW: How do you respond to signs of oxidation or reduction in a fermenting must? An aging barrel?
LB: Oxidation never really happens during fermentation. Reduction is quite rare at this stage, but if it happens, the answer is oxygen supply.
TS: We were lucky to have never seen signs of oxidation in our Pinot Noir, but if there is any reduction, we rack and take the lees out, then allow the wine to breathe. In 2016, we found maybe 30% of the lots needed to be racked; this year, it will only be 10%.
YP: Oxidation in a fermenting must is a strange bird! During fermentation, must is protected by the CO2 produced. If signs of oxidation are already apparent, they probably derived before even fermentation had stated. In any case, you need now to wait until fermentation finishes before you apply any anti-oxidation measures, such as the addition of those beloved sulfites. Reduction during fermentation, on the other hand, is a clear sign that the yeast is struggling to survive because of lack of nitrogen in a form that it can assimilate. An addition of some grams of inorganic nitrogen (DAP) will do the job on the spot.
CS: For must reduction, I use air during fermentation. Must oxidation is more complicated, but if the wine goes through malolactic, then the bacteria will “eat” the ethanol. If the oxidation is not too heavy, specifically in whites without malo, you can use some proteins to take out the phenols that are oxidized, but you start to lose quality. If an aging barrel is reduced, I rack and separate the wine from its heavy lees. If an aging barrel shows signs of oxidation, you have two major problems, depending on the intensity. One is organoleptic, i.e., how the wine tastes. The other is that when the oxidation is heavy, all the added SO2 becomes combined, and so there is no free SO2 (more specifically, molecular SO2) left to protect the wine from oxidation and microbes. So when it’s that heavy, you blend or dismiss the wine.
CL: It is very difficult to get oxidation in a must that is fermenting. As you know, by definition, a fermentation happens in a very reductive environment. Regarding reduction, we do not have much of those problems as we work with grapes that are sensitive to oxidation. We could suffer from oxidation in the post-fermentation maceration, but we do not give enough time for this to happen. Our whole process never goes longer than 18 days since the grapes are harvested.
KW: Are certain varieties more prone to oxidation/reduction? How is this managed?
LB: [Of the grapes we work with,] Grenache is oxidative, not the others.
YP: The answer to the question is governed by two factors: polyphenolic composition and pH of the must. The more a variety is rich in polyphenols, the more resistant it is to oxidation (polyphenols act as oxygen receivers), thus it is more likely to develop a reductive character. Syrah being the typical example of this case. The second factor is pH. A lower pH means a higher percentage of SO2 will be in a molecular form, and therefore the wine will be better protected against oxidation. It has to be made clear that pH level is not only a varietal attribute but is also due (mainly) to soil, soil nutrients, and grape maturity at harvest.
CS: This is a big discussion these days. Here, most of the winemakers say that Grenache is an oxidative variety, but I have a lot of Spanish friends that say this is because of the clone or selection that we use. For me, low acidity, high pH, and low levels of tannin make a variety more sensitive to oxidation. For me, Syrah and Pinot Noir are more sensitive to reduction, but this often depends on the style of fermentations. In these cases, I try to go to barrel with more clean wine, so I will not need to rack later.
KW: Do you ever stir the lees of your red barrels? Why or why not?
TS: We don't. I am not convinced of a gain in aromas for Oregon Pinot, or of a gain in complexity. But in the winery I worked with in France, there is an interest in working with lees in the context of longer aging and more new oak. But I keep my lees in case I need them for some specific matter.
YP: I used to do so. I have stopped. I do age my reds in barrels on their lees and, since it’s a rather long process, I prefer the slow autolysis assured through time rather than an accelerated one via stirring that could result in a higher risk of oxidation.
CS: No, because you lose the CO2 from the fermentation or malo, which protects the wine from oxidation naturally.
CL: We do not! Once the malolactic is finished we rack and incorporate the lees. They could be very reductive and have negative effect on the wine.
KW: Do you employ micro-oxygenation? What are the benefits of this, and what are the risks?
LB: No, I don’t. I tried. I don’t like it; it is nonsense. Oxygen is, in general, an enemy. So to bring it constantly is nonsense.
TS: We don't employ micro-oxygenation. Micro-oxygenation, if well employed, can help in some specific varieties to bind phenolics and enhance mouthfeel. This is not widely used in Pinot Noir, but I would be curious to see the results if some people do use it.
YP: Very little. Nevertheless, the fact that most people speak about micro-oxygenation and practically never about macro-oxygenation, has always puzzled me! In our winery, it’s macro-ox that we go crazy about. Macro-oxygenation is a technique that demands additions of oxygen to the fermenting must from 30 to even 100 times more than micro-oxygenating! Obviously, the goal is different. Micro is nice when you have either harsh tannins that you want to soften (polymerize) rapidly or when you are trying to get rid of undesired reductive aromas. Micro is applied on young wines, not fermenting musts, and mostly when you have cleared the malolactic phase. In our case, [with] Agiorgitiko, micro-oxygenation would be a rather bad idea, since those already soft tannins would be at risk to be demolished, and the wines would lose their structure. Macro-ox, on the other hand, during fermentation and extraction seems to be the ideal tool for convincing our soft, not-so-plentiful, and not-so-reactive tannins to rapidly react with anthocyanins, forming stable complexes, thus stabilizing color. As a bonus, yeasts are very happy and fruit is more expressive since no reductive odors are there to block the way. But one needs to have a soft touch when applying some six to eight milligrams of oxygen per liter per day for a good number of days—things can go seriously wrong!
CL: We do not use them. We have very round tannins, so this is not necessary for our wines. Micro-oxygenation also modifies the aromatic profile of the wine and does not help to maintain the typicity of each terroir.
KW: Do you ever employ délestage? Why or why not?
TS: Of course. We do employ délestage if the ferment gets a little stinky and reductive. So it is [a] tank-by-tank decision.
YP: Yes. Only with Syrah, to avoid bitterness, since punching down leads to bitterness in this case.
CS: In general, I don’t use délestage because it is too difficult to control the extraction that you will get, and too easy to over-extract. I think it can be a good tool if you want to extract fast, but not in my case.
CL: We never use délestage. We believe that this is a very strong intervention. You can damage a lot of the skins of the berries and over-extract, hiding the personality of terroir.
KW: Do you ever barrel down a wine before the fermentation is complete? Why or why not?
LB: Yes, sometimes. Finishing a red fermentation in barrel is interesting, more because of how the wine clarifies less than because of its relation to wood. I ferment all my whites in old barrels.
YP: Have never done it. I’m trying to see the interest of such an action…
CS: No, I prefer to finish the fermentation on the skins and then go to barrel.
CL: No, we have never done it.
KW: What are your approaches to pre- and post-fermentation macerations and why?
LB: I don’t go for technology. Pre- or cold fermentation goes against terroir.
TS: We don't do cold soaks; I personally don't see the advantage in the finished wines yet. We harvest by night and minimize the time between the harvest and the processing, so the fruit is consequently cool. We let the fermentation go naturally with no yeast addition. Post fermentation, we judge the quality of the tannins and will fine-tune by adding a pumpover or just not touching it while keeping it under a protective layer of gas.
YP: These are two fundamentally different things that need to be approached separately. Cold pre-fermentation maceration leads to better fruit expression and higher color intensity with a better, more vivid hue. Other polyphenolic indexes tend to have better values also (such as the BSA index, the polymerization HCl index, and the PVPP index), making this technique a must to practically all cases of red wine making regardless of the style of the wine. I utilize post-fermentation maceration only when the grapes are of immaculate health and impeccable phenolic maturity and I’m aiming for a long-aging, big red. It is to be avoided in all other cases.
CS: Pre-fermentation macerations are good for the extraction of color and aromas. I use post-fermentation macerations to round the structure, but you need to be very careful, because since there is alcohol, the extraction is greater. In general, I make this decision tank by tank; there is no recipe for this.
KW: Can pre- or post-fermentation macerations be taken too far? If so, what are the results?
YP: As for the pre-fermentation maceration, there is no need to exceed 48 hours. If you do, your gain will be unjustifiably low, where at the same time, the risk of a contamination with a cryophilic nasty yeast stain will go sky-high. For the post-fermentation maceration, there aren’t any musts or don’ts. Monitor your young wine. Taste it daily. You may sometimes find that although indexes such as TPI don’t really evolve that much during this period, the wine acquires complexity and depth—[though] that obviously does not mean that longer maceration is always better for the wine.
CS: Yes, during pre-fermentation macerations, the pH it will rise because of the contact with the skins. During post, it’s very easy to make a mistake on the extraction—one extra day with 14% alcohol can make a great difference. If you make long pre- and post-fermentation macerations, you will get wines with less acidity and more tannins. The problem is when winemakers make the wines by recipe, the wines lose the identity of place. It is better to decide place by place, tank by tank.
KW: How do you select the size of your barrels, the percentage of new oak, and the length of aging? How do each of these decisions relate to oxygenation?
LB: I am a fan of small barrels, as this is where the breathing works the best.
TS: We buy 228-liter barrels. The percentage of new oak is around 20%, and the wines spend 12 months in barrel. We use mostly French oak and few Hungarian barrels.
CS: New oak transpires more oxygen than a used barrel, because with time, the color and tartaric acid close the pores of the barrel, even if you clean it well. Bigger barrels offer less oak influence but also less oxygen, so the evolution will be slower. Length of barrel aging varies according to the wine, but wines with a high acidity and a high quantity of good-quality tannins we might age for two years or more.
CL: For us, aging is the redox exchange between the wine and the oxygen through the barrels. We normally age for 12 months. Anything longer would make the wine lose some of its primary aromas. Regarding the percentage of new oak, we vary depending on the structure of the wine. For example, for less complex wines we might use 20% new oak, whereas for our more complex wines we might use 70 to 80%. For Garnacha, we only use used barrels. The size of the barrels depends on how oxidative the grape variety is. We use 500-liter barrels for Monastrell and Garnacha and 225-liter barrels for Tempranillo.
KW: How often do you rack and why?
LB: I never rack [if] possible because this manipulates the wines and is never a good idea in terms of clarity. It also obliges us to use more SO2.
TS: We rack once during the 12-month élevage. We will rack a few lots sometimes if there is some potentially unpleasant reduction.
YP: Typically, we don’t rack. We will do so after having spent 12 to 14 months in 225- to 300-liter barrels, to place our blend in the second phase of its wooden maturation, which takes place in 15-hectoliter old oak foudres. Obviously, if any negative reductive aromas appear in the wine during its élevage in barrel, we rack immediately and without blinking twice. Fortunately, this is a rare scenario.
CS: In general, I rack the wines once, only when the malolactic fermentation is complete and the wine is ready to be separated from its heavy lees.
CL: We do not like to rack the wines. We only rack them once, once the malolactic happens.
I'm scratching my head, in the third paragraph, in the discussion of redox reactions. when elemental iron (Fe, oxidation state 0) "rusts" it is oxidized, with the resulting combination of Iron (II) oxide and Iron (III) oxide compounds occuring with the iron ion in a +2 and +3 oxidation state, respectively. So in the process of oxidation, the iron atom loses electrons, and in the process increases its oxidation state 0->+2 or +3. for the sake of redox reactions we alwasy assume diatomic oxygen molecules start at an oxidation state of 0 and go fully to their -2 state. so here the oxygen atoms decrease their oxidation state, and the oxygen atoms are said to be reduced. I remember the 10th grade chemistry aid "Leo goes Ger" Loess of electrons is Oxidation, gain of electrons is reduction. Okay. so this is a long way of saying that I don't understand the statement "A compound or element is “reduced” when it donates electrons to a bond, and is “oxidized” when it gains electrons" in fact i think it might be the other way around? Or perhaps I'm just misunderstanding the claim?
Hello! You are absolutely right, thank you for catching the mistake. We have made the change. My brain flipped the equation somehow. We appreciate your note.