By: Denise M. Gardner

Author’s Note: Current technical information regarding the production of pétillant naturels is limited. The following information is summarized and detailed from a series of text books and personal discussions with Paul Guyard from Enartis, Daniel Granes from the ICV in Languedoc-Rousillion, whose contact comes courtesy of Gordon Specht from Lallemand, and Michael Jones from Lallemand. The author would like to thank all contributors for the following information.

The recent interest in sparkling wine production (http://bit.ly/SparklingWineTechniques) has winemakers and sommeliers talking about another trendy bubbly: Pétillant Naturels, or pét-nats when abbreviated. These bubblies are consumer friendly: less expensive than traditional Méthode Champenoise-produced wine, usually contain an enhanced fruitiness, are meant to be consumed early (i.e., no long term aging required by the consumer), and are currently trendy amongst wine professionals, bloggers and sommeliers. A quick search online can lead one to a plethora of articles indicating consumer awareness of pét-nats:

Recent food trends indicate that consumers are searching for “more natural” selections (http://fortune.com/2015/05/21/the-war-on-big-food/), and pét-nats may appear as a less intrusive winemaking approach in the eyes of consumers. Pét-nats offer a winery marketing potential, as many are highlight as being made with limited technological influence and following more traditional winemaking practices.

The concept of production is rather simple: start fermentation and bottle before it is finished fermenting to retain some residual carbon dioxide, and likely sugar, in the final product. However, production requires winemaker attention to ensure final wine quality. As David Lynch quoted one producer in his Bon Appetit article, pét-nats production can seem like “Russian roulette winemaking” from the production perspective. Although in French, a detailed diagram displaying the steps of the méthode ancestrale production practices associated with pét-nats (follow the column labeled “méthode rurale”) can be found here: http://www.wine-and-bubbles.com/maj/phototheque/photos/schema/ShemaEtTexteCv4_3.jpg

History of Pét-nats

Pét-nats are believed to be the original source of sparkling wine production in France, preceding Champagne production (Robinson and Harding 2006). It is believed that wines from naturally-cooler regions in France would undergo primary fermentation until the winter when temperatures would naturally drop and inhibit fermentation. Winemakers, unaware that the wine was not fully fermented, bottled the young wine and found that it re-fermented in the bottle when the ambient temperatures became warmer. Some of the first sparkling wines produced have been traced back to Gaillac, located in the southwest part of France, north of Toulouse, and Limoux, located in the higher mountains of the Languedoc-Roussillon region (Robinson and Harding 2006).

The term “pétillant” generally describes a sparkling wine with less retention of carbon dioxide compared to a sparkling wine like Champagne (WSET 2001). The grape variety traditionally used for pét-nat production in Gaillac and Limoux is mauzac (known locally as blanquette in Limoux), which has a distinguishable “dried-apple-skin” flavor (Robinson et al. 2014). Today, pét-nat production has exceeded the boundaries of their origins, extending through the Loire and various regions around the world.

The production method associated with of Blanquette de Limoux is often referred to as the méthode ancestrale, or as the méthode gaillacoise in Gaillac (Robinson and Harding 2006). The methods are quite similar in execution, which consists of one primary fermentation that is started in tank and finished in the bottle. This results in a cloudy wine, typically with varying concentrations of residual sugar, and retention of carbon dioxide.

Thinking of Giving Pét-Nat Production a Try?

While the production of pét-nats may seem appealing, one of the experts suggested trying to bottle condition a wine before attempting the full méthode ancestrale production technique as it involves a lot of winemaker attention. This may also be a practical alternative when current production facilities are not equipped for full-range temperature control. Bottle conditioning is typically used by homebrewers, home cider makers, and home winemakers to get carbon dioxide in bottles. You can read some of the home production literature here if you are unfamiliar with the process:

It is recommended that you use a low alcohol (≤12% alcohol v/v), low pH (<3.50) wine if you are exploring the bottle conditioning technique. Add enough sugar to generate 3-4 ATM of pressure, maximum, and bottle with a yeast addition based on the suggestions below. Bottles should be suitable to retain pressure and sealed with a crown cap.

Bottle conditioning a wine should give you a clear indication regarding the finishing technique and style associated with pét-nats. It also acts as good practice before committing to pét-nat production.

Safety First

Since pét-nats are sparkling wine products that contain a fair amount of pressure, winemakers and cellar staff should proceed with caution during production. Use common sense: purchase appropriate bottles made to withstand pressure, double check calculations for sugar-to-pressure conversions, and use protective eye glasses. Accidents can happen, and it is best to be prepared for any hazard associated with any stage of wine production. Sanitation is a key point through production, and proper protective clothing should be worn at all times when using sanitizing agents of any kind.

Parameters to Look for in the Fruit

Pét-nat production may be applied to any grape variety, and offers a wide opportunity for winemakers to explore the production of new and unique wine products. Although there are no variety limitations, production experts caution that grapes should lack vegetal flavors in the berries.

Berry sensory analysis may be useful for winemakers to evaluate grape flavor quality and to help determine picking times. In general, ripe (non-vegetal) flavors should persist in the berry in order to encourage their development in the final wine. However, grapes should avoid “overly ripe” flavor characteristics as this may be an indication of higher pH and lower acidity values that may cause complications through the winemaking process.

Grapes are often picked with a potential alcohol of 10 – 12% v/v, and at this concentration of natural sugar, the pH should be lower (<3.50). The pH of the wine will offer microbial protection to the wine through the méthode ancestrale process and offer some protection to wine quality through vulnerable production steps.

Fruit should also be of sound quality (i.e., with limited disease pressure) to avoid detriment to flavor and overall quality of the wine. Some diseases may contribute secondary byproducts which could cause fermentation complications. Therefore, the winemaker is encouraged to use sound fruit. Cellar hygiene, or proper sanitation techniques, will be essential for quality control purposes through production. Extra sanitary care should be taken if the winemaker wants to remove the lees from bottles by traditional disgorging techniques (refer to a previous post on Sparkling Wine Production Techniques). A summary of grape parameters required for pét-nat production is shown in Figure 1.

Base Wine Production

The production method associated with pét-nats (Figure 2) is alluded to rather simply in the wine literature: the primary fermentation is started in tank, arrested before primary fermentation is completed, bottled, and finished in the bottle. The consumer can expect a slightly sweet (i.e., presence of residual sugar), cloudy, lightly bubbled wine (usually below 4 ATM pressure; Amerine et al. 1972). Winemakers should refer to the TTB for additional tax purposes associated with sparkling wines (http://www.ttb.gov/wine/wine_regs.shtml).

Grapes are crushed/destemmed (if preferred) and pressed. In France, press cycles and parameters are based on regulation. Press cycles are set to extract 100 L of juice for every 150 kg of fruit.

Some attention should be given to clarification of the juice, pre-fermentation, in the production process of pét-nats. It is recommended that juice is clarified to 30 – 80 NTUs with use of centrifugation, flotation or assistance with settling enzymes and/or fining agents.

There is some debate as to whether or not sulfur dioxide should be added to the juice during settling. In the juice-settling phase, a sulfur addition may help clarify the juice and minimize spoilage yeast and bacteria that could harm the quality of the wine. However, like with still wine production, sulfur dioxide additions should not be made to excess as too much could hinder primary fermentation. (Note: For those looking to produce a “more natural” wine, or to appeal to the “no-sulfur-added” market, it would be prudent to skip sulfur dioxide additions at this step.)

Following clarification, the juice should be racked and prepared for inoculation.

Starting Fermentation

Yeast selections (Table 1) should be based on the winemaker’s preference, but there are some tips that have been provided by wine supply companies:

Use low-sulfur dioxide-producing yeast strains

Select yeasts for secondary aroma potential

Supply yeasts with proper hydration and fermentation nutrient additions

Use yeasts that grow optimally in cool temperatures, 14-16°C (~57-60°F)

If the winemaker is going to remove lees (e., disgorging) before selling the product, and is only going to undergo one fermentation without a second inoculation, choose a yeast strain that is recommended for Méthode Champenoise sparkling wine production

Use a hydration nutrient (e.g., GoFerm Protect Evolution, Enartis Ferm Arom Plus) properly at inoculation. Depending on the winemaker’s preferred techniques or the perceived difficulty of alcoholic fermentation, oxygen additions can be made to activate the fermentation. Some winemakers choose oxygen ingress through the use of micro-ox, and base dosage rates [of oxygen] on sensorial perceptions.

Use of temperature control is essential for producing pét-nats. If you need more information and suggestions regarding how to integrate temperature control into your winery operation, please visit this report here: http://bit.ly/LowTempFerm.

Fermentation should proceed at 14-16°C (~57-60°F). At about +/- 3% v/v from the target alcohol, winemakers should chill the wine down to 8°C (~46°F) to hinder the fermentation. The act of cooling will also clarify the wine and minimize the transfer of lees. Too much lees transfer will result in a “yeasty” flavored wine, which is not preferred in pét-nat wines.

Finishing the Wine

Once the wine is properly chilled, it will need to be racked to remove most of the lees. It is not uncommon for winemakers to remove all of the lees by centrifugation or filtration, and later, restart the wine with a fresh culture and hydration nutrient. From a French winemaking perspective, the addition of nitrogen is usually added at racking in the pump flow (1 L of nitrogen gas for each 20 L of wine).

Winemakers may opt to blend at the racking stage as well. Blending can help elicit the production of a “house-style” pét-nat, and ensure consistency despite natural vintage year variation.

Malolactic fermentation is optional, and should be inoculated after racking, based on winemaker preference. For those that are considering malolactic fermentation, it is important to remember that there is a significant quantity of residual sugar in the wine at this stage in the process, which can lead to a series of winemaking problems:

Consider the wine’s pH before undergoing malolactic fermentation. Malolactic bacteria have a higher risk of producing more acetic acid during malolactic fermentation if the wine pH is greater than 3.50. Great attention and care must be given to a pét-nat undergoing malolactic fermentation with a higher pH to avoid extreme spoilage issues.

Malolactic bacteria require a warmer temperature for growth, which requires the winemaker to increase the temperature of the wine. Therefore, it is suggested that winemakers sterile filter the wine prior to inoculating for malolactic fermentation to avoid primary fermentation from re-starting and completing before the wine is bottled.

The remaining residual sugar puts the wine at risk for other microbial contaminants. Sanitation and monitoring of malolactic fermentation progression is of the utmost importance.

Tartaric acid stabilization, or cold stabilization, can progress at this stage after the wine is racked. However, it is more common for winemakers to add CMC to avoid crystallization of tartaric acid as opposed to undergoing a cold stabilization process.

At this point, the wine should be prepared to complete primary fermentation. If the wine were to go to tank and complete fermentation, then the process of completion follows a Partial Fermentation process that is used in the Asti region of Italy to produce Moscato.

To complete the méthode ancestrale technique, the base wine is bottled to complete fermentation. A second inoculation of yeast is typically required to complete primary fermentation, but it is optional to add more yeast nutrient at inoculation. Some wineries choose a second edition of a hydration nutrient (prepared during yeast hydration) and a smaller dose of a complex nutrient (e.g., Fermaid K, Nutriferm Advance). Yeast addition dosage rate is recommended at about 2 million colony forming units (CFU) per mL of living yeast. Ideally, yeast addition should be less concentrated than a “normal” inoculation to minimize biomass in the bottle and encourage a slow fermentation in the bottle. Yeast strain should be selected according to winemaker preference (see the above list, Table 1, for suggestions from Lallemand/Scott Labs and Enartis Vinquiry).

Méthode ancestrale does not involve a sugar addition at the second inoculation. However, a sugar addition to manipulate the final desired concentration of pressure in the bottle is an option for winemakers at the second inoculation of yeast.

Bottle selection is important, and needs to be of high enough quality to retain the internal pressure left over from fermentation. If the expected pressure is above 4 ATM, ensure that you are using the correct bottles to retain pressure. Yeast selection should also be altered if the final preferred pressure is greater than 4 ATMs.

Although a slight detour from the méthode ancestrale process, it is possible to remove the lees after fermentation has completed in the bottle. If the winemaker would like to riddle and disgorge the yeast at the completion of primary fermentation in the bottle, a riddling agent (e.g., Adjuvant MC by Enartis Vinquiry) may be desired.

After the base wine is re-inoculated in the bottle, bottle fermentation should progress in a temperature controlled space, optimally set at 13-15°C (~55-59°F). For retention of residual sugar, chill the room to 0-2°C (32-36°F) to arrest fermentation in the bottle. [Note: When the wine is warmed up, it may continue to ferment in the bottle.]

With the minimal yeast population, minimal nutrient availability, increase pressure in the bottle, and low fermentation temperature, fermentation will progress slowly and may stop with residual sugar naturally as all of these factors put stress on the yeast. It may take several months until an appropriate amount of pressure has built up in the bottle.

Potential Disgorgement

Some winemakers choose to sell a product that is clearer than traditional pét-nats and disgorge the yeast lees using similar techniques that were previously discussed pertaining to the traditional method, Méthode Champenoise, way of making sparkling wine. Here, the lees are collected, riddled, and disgorged. If the wine was fermented to dryness, a sugar addition with a dose sulfur dioxide can minimize risk for re-fermentation when the bottle is in the hands of consumers. Furthermore, disgorgement allows a winemaker to make sensory alterations to the wine with a dosage addition. Sensory adjustments can be made using Arabic gums, inactivated yeast/polysaccharide products, or tannins that have been added to the dosage.

Traditionally, pét-nats are sealed with a crown cap.

Final Production Thoughts

Large producers of bottle conditioned cider may opt to flash bottle pasteurize hard ciders that retain some residual sugar. Flash bottle pasteurization will inactive the yeast and ensure an extra line of protection to ensure that fermentation does not continue to progress once the consumer has purchased the product.

However, part of the fun associated with pét-nats is not truly knowing the end residual sugar!

Note: Do NOT add potassium sorbate to the wine at any stage if you are trying to make a pét-nat. Potassium sorbate will inhibit the yeast from fermenting through any stage of this process.

Familiarizing Yourself with Pét-Nats

Like with any wine style, it is ideal to have a sensory library of what quality pét-nats taste like using examples from the commercial market. The practice of tasting multiple examples of a specific wine style creates a benchmark library in the mind of the winemaker, which aids in making processing decisions in relation to an end-goal for the final product. It also helps define “quality” for that wine style.

While I have not embarked on an exploration to understand pét-nat quality, the following wines have been suggested in the above-mentioned articles or from individuals that have enjoyed pét-nats in today’s market. I highly suggest that any winemaker aiming to produce pét-nats, obtain various examples to evaluate 1) their individual preference of the product, 2) the potential consumer preference of the product, and 3) the quality parameters that the winemaker will aim for during production of a pét-nat style wine.

References

Amerine, M.A., H.W. Berg, and W.V. Cruess. 1972. Technology of Wine Making, Third Edition. The AVI Publishing Company: Westport, Connecticut.

Granes, Daniel. 2015. Personal Discussion.

Guyard, Paul. 2015. Personal Discussion.

Jones, Michael. 2015. Personal Discussion.

Robinson, J. and J. Harding. 2006. The Oxford Companion to Wine. ISBN: 978-0198609902

Robinson, J., J. Harding, and J. Vouillamoz. 2014. Wine Grapes.

Wine and Spirit Education Trust (WSET). 2011. Wine and Spirits: Understanding Style and Quality. ISBN: 978-1 905819 15 7.