When making one’s own wine, few producers have never hesitated over the choice of whether to ferment with active dry yeast or to rely on indigenous microorganisms—so-called “wild” yeasts—present on grapes and in the winery.
If the priority is fermentation reliability and operational safety, choosing fermentation with active dry yeast is the most dependable option. With active dry yeast, fermentation kinetics are relatively reproducible, and alcoholic fermentation can usually be brought to completion with fewer unexpected deviations.
By contrast, spontaneous fermentation driven by wild yeasts increases uncertainty in microbial succession and metabolic behavior during fermentation. It is well known that this heightened uncertainty raises the risk of incomplete fermentations, including sluggish or stuck fermentations. It has also been pointed out that spontaneous fermentation can increase the likelihood of forming compounds responsible for off-flavors, thereby elevating the risk of sensory faults in aroma and taste.
Despite these risks, an increasing number of producers in recent years have avoided active dry yeast and have chosen spontaneous fermentation using indigenous microorganisms associated with their grapes or winery. Behind this choice is not only a desire to move away from an “industrial” image, but also the idea that spontaneous fermentation may reflect local terroir more directly and may yield more complex sensory profiles. In this view, commercially available active dry yeasts—because they are widely distributed and used by anyone—are seen as limited in their ability to express the individuality of a given place.
At the same time, fermentation problems can be fatal for a winery. For that reason, long before the development and widespread use of active dry yeast, substantial effort was devoted to stabilizing fermentation. One traditional technique developed and used in this context is Pied de Cuve.
This article explains Pied de Cuve as a method for achieving a more stable form of spontaneous fermentation in winemaking.
Pied de Cuve as a Winemaking Method
Preparation and use of Pied de Cuve begins before the main fermentation. The key concept is to run a preliminary fermentation prior to the main fermentation.
A small quantity of grapes is harvested before the main harvest, and the juice obtained from this early harvest is fermented. The fermenting juice is then inoculated into the juice intended for the main fermentation. Through this addition, yeast cells are transferred from the actively fermenting juice into the main must, where they act as a starter and promote fermentation. In this context, “Pied de Cuve” refers to the fermenting juice prepared as a starter to initiate fermentation in the main must.
In general practice, Pied de Cuve is prepared without active dry yeast, and fermentation is initiated by wild yeasts. In a broader sense, however, some sources also refer to a pre-culture prepared with active dry yeast as Pied de Cuve. In this article, Pied de Cuve is defined specifically as a starter prepared through spontaneous fermentation by wild yeasts.
Pied de Cuve literally means “the bottom of the barrel.” As the etymology suggests, it was named after the observation that adding fresh juice onto yeast sediment at the bottom of a barrel can trigger rapid fermentation. In sparkling-wine production, particularly in Champagne where a secondary in-bottle fermentation is carried out, Pied de Cuve has traditionally been used as a technique to promote yeast growth and adaptation to the environment, thereby supporting a more reliable secondary fermentation.
A similar approach is known as back-sloping. Both methods share the principle of obtaining yeast from a fermented juice and using it for the main fermentation. The difference lies in the timing of yeast collection. In back-sloping, yeast is collected when fermentation is nearly complete, whereas in Pied de Cuve, yeast is obtained during the early to mid stages of fermentation, when activity remains high.
Two Advantages of Pied de Cuve
Reducing Risk by Shortening the Waiting Time Before Fermentation Starts
One benefit often attributed to Pied de Cuve is that, in some cases, it can reduce the waiting time before the main fermentation begins to nearly zero.
Grape must typically requires a waiting period of several hours to several days before fermentation starts. This is because the yeasts responsible for fermentation must first multiply in the must, increasing their population, and only then begin to metabolize the sugars in the juice at a rate that manifests as active fermentation. In other words, the “waiting time” before fermentation begins corresponds to the yeast growth phase: it becomes shorter when yeast growth is rapid, and longer when growth is slow.
Pied de Cuve functions as a fermentation starter. Because it already contains a high yeast cell density, adding it to the main must can trigger fermentation after only a short delay. In some cases, fermentation may begin with virtually no observable waiting time.
Why, then, is this behavior a major advantage of Pied de Cuve?
Certainly, eliminating the waiting time can shorten the overall production timeline by several days. More importantly, however, the value is not the time savings themselves, but their consequences. A long delay before fermentation begins is a major factor associated with subsequent fermentation problems and sensory faults. By shortening this waiting time, Pied de Cuve can reduce the risk of such negative outcomes, and this risk reduction is a key practical advantage of the method.
The Reality That Spontaneous Fermentation Often Has a Long Waiting Time
As a baseline, when spontaneous fermentation is carried out without adding active dry yeast, the waiting time before fermentation begins tends to be relatively long. During this extended period, non-Saccharomyces yeasts frequently become active.
The Relationship Between Saccharomyces and Non-Saccharomyces Yeasts
Even in spontaneous fermentation, the primary drivers of alcoholic fermentation are, in most cases, yeasts of the genus Saccharomyces. Among them, Saccharomyces cerevisiae is particularly important. Most active dry yeasts currently on the market also belong to Saccharomyces.
Many non-Saccharomyces yeasts are less well adapted to the winemaking environment than Saccharomyces yeasts and are unable to carry fermentation through to completion. Their overall fermentative capacity also tends to be weaker than that of Saccharomyces. Regardless of whether active dry yeast is added, wines that have fermented to near-zero residual sugar are in most cases the result of fermentation dominated by Saccharomyces yeasts.
This means that even when spontaneous fermentation is chosen, a robust onset of alcoholic fermentation requires waiting for Saccharomyces yeasts to multiply. However, many non-Saccharomyces yeasts grow faster than Saccharomyces and can, at times, inhibit Saccharomyces growth.
Why Spontaneous Fermentation Starts Late and Why Faults Are More Likely
Such microbial competition can extend the period during which non-Saccharomyces yeasts remain active and delay the onset of fermentation driven by Saccharomyces. If Saccharomyces growth is strongly inhibited, the outcome may escalate to major problems such as sluggish fermentation or a complete arrest.
Another characteristic of non-Saccharomyces yeasts is that their metabolism often differs from that of Saccharomyces. They can produce large amounts of compounds that Saccharomyces would not produce, or would produce only in trace amounts. Some of these compounds may contribute to complexity in wine. At the same time, others can lower wine quality, including ethyl acetate and acetic acid.
While there is great diversity among non-Saccharomyces yeasts, certain lineages are known to occur at relatively high frequency on grape skins. It is also understood that some of these yeasts tend to produce comparatively large amounts of compound classes that negatively affect wine quality, such as volatile acidity.
The longer non-Saccharomyces yeasts remain active—that is, the longer the waiting time before fermentation— the higher these risks become. For this reason, the use of Pied de Cuve, which can shorten or nearly eliminate the waiting time even within spontaneous fermentation, is regarded as an effective approach.
Selecting Yeasts
The second advantage of Pied de Cuve is the selection of suitable yeasts and their adaptation to the fermentation environment.
Roughly 2,000 yeast species have been identified to date, but it is considered likely that more than 100 times that number may exist in reality. Among this vast diversity, it is unclear how many strains exert beneficial effects on wine. Nevertheless, maintaining or improving wine quality requires selecting yeasts that are more suitable for winemaking.
When spontaneous fermentation is used, the strains responsible for fermentation cannot be chosen in advance. Moreover, in spontaneous fermentation, the reproducibility of yeast dynamics remains low not only between vintages but even between batches within the same vintage. Even if one vintage yields favorable results, there is no guarantee that the next vintage will behave similarly. Spontaneous fermentation is often said to reflect terroir, but in practice the reproducibility of the yeast community is not part of what is reliably “reflected.”
In other words, it is impossible to know in advance which yeasts will dominate in a given tank, and it is also impossible to control them precisely. Given the diversity of yeasts in nature, this represents a substantial risk. This is one reason why Pied de Cuve was developed as a fermentation management technique.
With Pied de Cuve, it is possible—through several operational choices, including whether or not to add the prepared starter to the main fermentation—to select, to some extent, the yeasts that will be involved in the main fermentation. This selection is not as strict as the strain-level control achieved with active dry yeast. Rather, it is a coarser selection at the community level. Even so, community-level selection can suppress a wide range of fermentation risks to a considerable degree.
Preparing Pied de Cuve and Selecting Yeasts
There are two ways to apply selection through Pied de Cuve preparation. One approach is to prepare multiple Pied de Cuve batches simultaneously and choose the one that exhibits more desirable characteristics. The other approach is to prepare a single Pied de Cuve in multiple stages.
The first approach is more commonly used in practice. Because a starter can be selected from among multiple candidates, it allows the producer to use a Pied de Cuve that more closely matches the desired characteristics. However, as a drawback, batches that are not selected are generally discarded, which increases material loss.
By contrast, the second approach can be operated without generating such losses.
The second approach is also referred to as the scale-up method (SUM). In this preparation method, a small initial Pied de Cuve is increased gradually through two or three stages.
In SUM, the Pied de Cuve is typically transferred, a few days after the initial juice begins fermenting, into a new volume of juice approximately twice the original amount. Then, after several more days, it is transferred again into a volume several times larger. By repeating this operation multiple times, the Pied de Cuve is scaled up; finally, when it has been increased to roughly 5% of the main-fermentation must volume, it is used to initiate the main fermentation.
Each time the Pied de Cuve is transferred to fresh juice in SUM, the prior competitive balance among yeasts is effectively reset. At the same time, yeasts that have already begun proliferating can be carried over without a reduction in cell numbers. As the scale-up steps are repeated, selection therefore proceeds in practice around the yeasts that are already dominant.
Unlike preparing multiple batches, SUM does not allow intentional choice of which yeasts will be selected. On the other hand, it avoids juice loss associated with Pied de Cuve preparation, and the comparatively long preparation period can allow yeasts to adapt more effectively to the fermentation environment. This can be expected to stabilize fermentation behavior and to reduce the risk of sensory faults.
Conclusion: To What Extent Can Pied de Cuve Control Spontaneous Fermentation?
Within the modernization of winemaking, the use of active dry yeast has been a core technology with significant impact. Because this technology became widely adopted, wine quality improved substantially compared with earlier periods. At the same time, it has also been widely argued that the spread of active dry yeast contributed to global homogenization of wine styles.
This homogenization has, in turn, fed into the broader context of the industrialization of winemaking. As an antithesis to that trend, a preference for what is often called “natural wine” has emerged.
Although the peak of that movement has somewhat subsided compared with earlier years, wines labeled as “natural” or “naturally made” remain strongly popular. At the same time, there are no official public standards for this category, and a wide range of wines are sold under the label of natural wine.
The situation can appear to be a “whoever claims it wins” environment, but one element often regarded as important in defining this category is the use of spontaneous fermentation with wild yeasts. It is difficult to deny that the growing attention many producers now give to spontaneous fermentation has been influenced, at least in part, by the natural-wine movement and the ideas associated with it.
In recent years, global climate change and warming have increased the activity of microorganisms involved in winemaking. As a result, phenomena that were previously suppressible have become harder to control with the same methods. Unintended influences from lactic acid bacteria and Brettanomyces are typical examples.
In environments where microbial effects become more pronounced, spontaneous fermentation with no control measures brings a higher risk of microbial contamination into the cellar than in the past. Even as interest in spontaneous fermentation rises, the risks associated with that choice are, in reality, increasing.
For that reason, using methods such as Pied de Cuve to control spontaneous fermentation has gained substantial importance.
Multiple investigations support the likelihood that the use of Pied de Cuve can enable spontaneous fermentation without deterioration in wine quality. There are also reports that wines made with Pied de Cuve exhibit characteristics closer to spontaneous fermentation than wines made with active dry yeast. Pied de Cuve can therefore be considered one rational means of producing wine through spontaneous fermentation.
The Significance and Limits of Pied de Cuve
Pied de Cuve is a starter aimed at enabling more reliable fermentation, but its essence is not the strain-level management of yeast through selection. Rather, it lies in managing yeasts at the community level—preserving the meaning of spontaneous fermentation—while regulating fermentation dynamics over time.
Many reports indicate that Pied de Cuve can improve wine quality, but Pied de Cuve does not necessarily guarantee defect-free winemaking. There are reported cases in which yeast strains detected in the Pied de Cuve were no longer present in the liquid toward the end of alcoholic fermentation, indicating that Pied de Cuve does not fully determine the wine’s direction. It has also been noted that, even when Pied de Cuve is inoculated, significant delays or arrest can still occur in subsequent fermentation. Unfortunately, Pied de Cuve is not a magic wand that can fully control spontaneous fermentation.
What Pied de Cuve controls is not fermentation itself, but the adjustment of its dynamics. By using this technique, it becomes possible to modulate—within a time frame—the direction of spontaneous fermentation and the formation of the yeast community, which would otherwise be unmanageable. Even so, uncertainty in fermentation remains. To refine this adjustment further, a deeper understanding of Pied de Cuve beyond what has been discussed here is required.
What is spontaneous fermentation? What is Pied de Cuve? The essence of those answers does not stop at the simple choice of not using active dry yeast.
