Oxidation is widely recognized as one of the causes of wine deterioration. When a bottle is opened and the wine becomes more exposed to oxygen, this chemical reaction progresses more noticeably. For this reason, oxygen is generally considered to be the cause of oxidation.
However, there are two types of wine oxidation: enzymatic oxidation, which does not directly involve oxygen, and non-enzymatic oxidation, in which oxygen is the direct cause. Most of the oxidation we experience as wine deterioration is caused by a chemical reaction called enzymatic oxidation. In this reaction process, enzymes play a more important role than oxygen. In other words, oxygen is not as important a direct cause as is generally believed.
In recent years, with the rise of natural wines and changes in winemakers' attitudes, approaches to wine oxidation have become more diverse. Within this trend, a foundation has been forming to accept mild oxidation as part of a wine's character. On the other hand, excessive oxidation that can be called deterioration continues to be something that should be avoided. And regardless of how oxidation is handled, oxygen remains the central focus when considering this topic.
This article examines the possibilities for preventing wine oxidation while also considering the nature of wine as natural wine.
Exploring Natural Methods to Suppress Wine Oxidation
One effective means of preventing wine oxidation is the appropriate addition of sulfur dioxide (SO2), known as an antioxidant.
However, against the backdrop of the recent natural wine boom, many negative opinions have been expressed by both consumers and producers regarding the addition of sulfites to wine. When sulfites are added, there is an increasing trend to reduce them to the minimum necessary level, or even below that. The misconception that sulfites in wine cause headaches when drinking wine also continues to be strongly believed.
To respond to the philosophy and demands of adding as little sulfite as possible, methods are needed to sufficiently protect wine from oxidation without relying on sulfites. Many winemaking techniques aimed at reducing changes in wine due to oxidation have been researched, and multiple methods have been put into practical use. However, most of these techniques involve mechanical processing. This does not align with the natural philosophy of avoiding human intervention in winemaking as much as possible, making adoption difficult in winemaking settings.
In this context, there exists one oxidation suppression method that is extremely well-suited to natural philosophy: using wine lees.
The Relationship Between Lees and Oxidation Prevention
When considering wine oxidation, there are three elements that play important roles: enzymes, phenolic compounds, and oxygen.
In enzymatic oxidation, which accounts for most wine oxidation, the center of the reaction is enzymes and phenolic compounds. However, this does not mean that the presence of oxygen can be ignored. There is no doubt that as the amount of oxygen in wine increases, the risk of wine oxidation increases. These three elements exist in one continuous cycle. This indicates that acting on any one of these three elements will, to a greater or lesser extent, affect the overall oxidation action of the wine.
Sulfur dioxide acts primarily on enzymes and phenolic compounds, as well as compounds produced in oxidation reactions. In contrast, wine lees—more specifically, the yeast that is the main component of lees—act on the oxygen in the wine. Yeast cells can adsorb dissolved oxygen in the wine.
When oxygen is removed from wine by yeast, or lees, one of the three important elements related to wine oxidation is lost. This suppresses wine oxidation.
Do Cloudy Wines Not Oxidize?
One of the styles that represents natural wine is unfiltered finishing. In unfiltered finishing, where wine is not filtered when bottling, depending on the production method, wine is bottled in a strongly cloudy state. Recently, there has been a trend favoring such cloudy wines, and a considerable number of cloudy wines are displayed on wine store shelves. The main cause of such cloudiness is lees.
If lees reduce the amount of dissolved oxygen in wine and consequently protect wine from oxidation, it can be considered that cloudy wines have relatively high resistance to oxidation. And if wine has high oxidation resistance, the need to add antioxidants decreases. As a result, it seems correct that wines without added sulfites should have a cloudier finish.
If finishing wine unfiltered and leaving strong cloudiness can suppress both the addition of antioxidants and wine oxidation, nothing could be more convenient for aiming to make natural wine. Among wines called natural wines, some seem not to change in taste even after being left for several weeks or more after opening. These wines appear to be completely unaffected by oxidation.
After hearing that lees adsorb dissolved oxygen in wine, when drinking such wines, one might think that it is all because the lees in the bottle are protecting it from oxidation. Unfortunately, this is not the case. Even if lees are present, wine oxidizes.
Why Does It Taste Better After Opening for a While?
Many cloudy wines feel more delicious several hours, or even several days, after opening the bottle rather than immediately after opening. There are multiple possible reasons for this, one of which is recovery from a reduced state caused by lees.
When bottled wine contains a lot of lees, there is a possibility that the wine is in a more reductive state through the oxygen adsorption action of the lees. In wine in a reductive state, a characteristic odor called reduction can be felt, and this odor sometimes gives a negative impression to the wine. While severe reduction is difficult to remove, mild reduction can be removed by swirling, decanting, or simply letting the wine sit after opening.
There are multiple other possible reasons why wine feels more delicious after opening for a while—the so-called "opened" state. Also, wine containing lees is not necessarily in a reduced state. However, it is also true that bottles containing a lot of lees have a relatively higher possibility of being in such a state. In such bottles, there is a possibility that the reductive state of the wine is resolved through contact with oxygen, and the wine becomes more enjoyable as the unpleasant odor is no longer felt.
Reference video: YouTube channel "Thinking About Wine with Nagi" Let's Think with Winemakers: What Does It Mean for Wine to Open?
Lees Suppress but Do Not Prevent Oxidation
Lees certainly adsorb dissolved oxygen in wine and protect wine from oxidation through such behavior. However, through many studies, it has become clear that there is very large and unpredictable variation in the dissolved oxygen adsorption effect by yeast cells.
For example, if yeast cells adsorb oxygen, it would seem that more cells would adsorb more oxygen. In other words, it would seem that wine with stronger cloudiness would have higher oxidation resistance.
This seems correct at first glance, but it is actually wrong.
Studies to date have not been able to identify factors that affect the amount of oxygen adsorption. This means that even if the amount of lees is large, the amount of oxygen adsorption is not necessarily large. There is no proportional relationship between the number of yeast cells and the amount of oxygen adsorption. Also, while it is known that the type of yeast strain also makes a difference in the amount of oxygen adsorption, variation in study results is large even on this point, and clear differentiation by strain type has not been established.
Most importantly, lees do not adsorb 100% of the dissolved oxygen in wine. Even in bottles containing lees, oxygen always remains. And that oxygen affects the oxidation reaction of wine. While the presence of lees may make wine less likely to oxidize, it does not completely prevent oxidation.
Is Oxidation Prevention Through Cloudiness Beneficial?
Even if cloudiness is left in the bottle, wine oxidation cannot be completely stopped. However, on the other hand, the reaction can be suppressed and its progress can be slowed somewhat. Even if oxidation cannot be completely prevented, if it can be made to progress slowly, depending on one's way of thinking, this can be a reason not to add antioxidants.
In the first place, if we think within the framework of natural wine, both adding sulfites and filtering are considered acts that should be avoided. Within that framework, being able to avoid adding sulfites through bottle cloudiness resulting from not filtering is superficially a very convenient development.
However, in reality, things do not work out quite so conveniently. This is because handling lees is very difficult. Even looking only from the perspective of oxidation prevention, it is not a simple matter of just leaving it cloudy.
What adsorbs dissolved oxygen in wine are yeast cells. In other words, unless the main component of the lees is yeast cells, no matter how cloudy the wine is, oxidation prevention effects cannot be expected. While it is often thought that lees are naturally made of yeast residue, in reality their composition varies. Depending on the environment in which the winery or fermentation vessel is placed, lees can also be caused by microorganisms completely unrelated to yeast.
Additionally, it is important to note that lees often contain components that promote wine oxidation. Lees are not made of a single component but are always a mixture of multiple components. Among these components, it is not uncommon for substances with contradictory effects and influences to be present simultaneously. Even if one component has an oxidation-preventing effect, another component may simultaneously be promoting oxidation. When components with multiple different directional effects are present simultaneously, the resulting outcome varies depending on the magnitude of each component's influence. For example, even if an oxidation prevention effect is strongly manifested at a certain point in a certain environment, it is entirely possible that an oxidation promotion effect will be strongly manifested at a different point in a different environment.
Not limited to the perspective of oxidation prevention, cloudiness does not necessarily guarantee the expected effects. Rather, the presence of lees introduces more uncertain factors into the bottle and glass. For this reason, it is necessary to operate on the assumption that the lees in the bottle may have some negative effect on the wine, and that this possibility is not low.
To more effectively utilize wine cloudiness from an oxidation prevention perspective, it is necessary to know what kind of properties the components of that cloudiness have. However, in winemaking environments without human intervention, such as spontaneous fermentation with wild yeast, the constituent components of lees can change greatly each time. Certainly, cloudiness left in bottles may sometimes suppress wine oxidation and become an effective means to achieve non-addition of SO2. However, given the instability of the effect itself and considering other effects that lees may have on wine, expecting wine cloudiness as a means of oxidation prevention can be said to be a high-risk endeavor.
