Hygiene in the Wine Cellar: The Invisible Pillar of Wine Quality

Because microbiology, cleanliness, and sanitary control determine the success — or failure — of a wine.

When we think about the factors that determine the excellence of a wine, aspects such as the quality of the grapes, the terroir , the winemaking techniques, and aging quickly come to mind. However, there is a fundamental element that rarely receives the attention it deserves from the public: hygiene in the winery. This component, although invisible to the eyes of the end consumer, can determine whether a wine with potential will become a masterpiece or a product with irreparable defects.

The False Sense of Security with Wine

As the renowned oenologist Émile Peynaud stated, wine conveys a false sense of safety and cleanliness, while in reality it is extremely susceptible to contamination. This observation, made decades ago, remains perfectly relevant today. Despite its acidic pH and alcohol content, which effectively prevent the growth of pathogenic microorganisms dangerous to human health, wine is highly susceptible to microbiological changes caused by organisms that significantly affect its organoleptic quality.

The wine industry is subject to regulations, including Good Manufacturing Practices (GMP) that establish hygiene and processing requirements, classifying wineries as food processing facilities. This classification is not merely bureaucratic, but reflects the critical importance of sanitary procedures in production.

The Invisible Enemies: Disease-Destroying Microorganisms

Throughout the winemaking process, from receiving the grapes to bottling, there are numerous stages where poor hygiene practices can cause irreparable losses in the quality of the final product. The main groups of spoilage microorganisms include:

Lactic and Acetic Bacteria

Lactic acid bacteria can break down sugars and produce increases in lactic acid, being responsible for defects such as "fatness," which gives the wine an oily consistency. These bacteria are particularly problematic during the vulnerable period between the end of alcoholic fermentation and the completion of malolactic fermentation, when sulfur dioxide levels must remain low so as not to inhibit the desirable malolactic bacteria.

Acetic acid bacteria , in turn, represent one of the most critical and easily irreversible microbiological risks in oenology. Belonging mainly to the genera Acetobacter and Gluconobacter , these bacteria are strictly aerobic, meaning they depend on the presence of oxygen to develop . Their activity is directly associated with the oxidation of ethanol into acetic acid, leading to an increase in volatile acidity—one of the most penalized defects from a legal, sensory, and commercial standpoint.

The proliferation of acetic acid bacteria is favored by:

• Excessive presence of oxygen (poorly controlled transfers, underfilled tanks, sealing failures)

• Damaged or rotten grapes

• High temperatures

• Low levels of free sulfur dioxide

• Prolonged periods of contact with contaminated coarse sludge

In addition to acetic acid, these bacteria can produce ethyl acetate in high concentrations, resulting in intense aromas of varnish or glue that quickly dominate the wine's aromatic profile. It is important to emphasize that the defect caused by acetic bacteria is cumulative and irreversible : once certain thresholds are exceeded, there is no effective technological correction without significant loss of identity and quality.

Alteration Yeasts

Among problematic yeasts, Brettanomyces bruxellensis deserves special mention. Brettanomyces is a ubiquitous spoilage yeast that can impart intense barnyard aromas to wine, especially in barrel-aged red wines. This yeast is particularly insidious due to its alcohol tolerance, ability to utilize residual nutrients, and skill in forming biofilms on equipment surfaces.

Recent scientific studies demonstrate the complexity of the problem. Investigations have revealed that hard-to-reach surfaces such as valves, taps, and wall corners show high levels of yeast contamination, indicating low hygiene levels in these critical areas. The presence of bioadhesive cells and biofilms in contact with wine results in a significant release of cells into the liquid, leading to population growth and the production of volatile phenols in concentrations exceeding the olfactory detection threshold.

Molds and Fungi

Molds can cause defects such as "brown or oxidative rot" and impart pronounced musty flavors, attacking damp containers in cellars. The genera Penicillium and Aspergillus are the main culprits behind these problems, especially in environments with high humidity and insufficient ventilation.

The Triple Approach: Cleaning, Sanitizing, and Sterilizing

Proper hygiene management in a wine cellar relies on understanding three distinct but complementary concepts:

Cleaning refers to the physical removal of dirt, organic residues, tartrates, dyes, and other materials from surfaces. This is the fundamental step, as no sanitizer can work effectively on dirty surfaces. It is not possible to sanitize something that is not clean; therefore, a combination of surfactants, detergents, and mechanical action is essential.

Sanitization involves reducing the microbial load to safe levels through chemical or physical agents. The main agents used include:

• Peracetic acid : effective against a broad spectrum of microorganisms, leaves no residue and requires no final rinsing.

• Sulfur dioxide : traditional in oenology, especially effective when in molecular form.

• Hot water : temperatures above 80°C are very effective; filling barrels with water at 85°C for 15 minutes is recommended.

• Nitrogen : recently gained attention for its effectiveness against microorganisms and its ability to clean without leaving residue on treated surfaces.

Sterilization is the complete elimination of all microorganisms. Although ideal, true sterility is rarely achieved in wineries; instead, microbial reduction levels are achieved that are compatible with the safety and quality of the wine.

Practical Hygiene Protocols

Implementing an effective hygiene program requires systematization and discipline. Alternating detergents is recommended: four days a week use an alkaline (caustic) detergent followed by a peracetic acid sanitizer, and on the fifth day use an acidic cleaner to remove mineral deposits.

Critical Areas of Attention

Scientific studies have identified areas that are particularly vulnerable to contamination:

1. Transfer equipment : hoses, pumps, and connections are primary vectors of cross-contamination.

2. Valves and taps : these hard-to-clean areas have yeast populations between 8×10⁻² and 6.4×10³ CFU/cm².

3. Oak barrels : some resident yeast strains can feed on cellobiose in oak wood, making the wood a persistent reservoir.

4. Floors and drains : often-neglected areas that can harbor significant microbial populations.

5. Bottling equipment : the last line of microbial defense requires special attention.

Biofilm Management

Biofilms present a particular challenge. Some microorganisms utilize nutrients from must and wine to form polymers, aggregating on surfaces and creating biofilms with protective layers resistant to many chemical cleaners. Biofilm removal generally requires physical action (brushing, high pressure) in addition to chemical treatment. One suggested treatment involves the use of caustics at 75°C for 30 minutes, followed by rinsing with citric acid.

The Role of Water in Wine Cellar Hygiene

The quality of water used in the winery is fundamental. The water used in the preparation of wine products, the sanitization of storage tanks, and the production of steam must be suitable for human consumption. Studies show that the average rate of wastewater generation in wineries has been reduced to 1.58 L per liter of wine produced, reflecting more efficient water management practices, but also highlighting the significant volume of water needed to maintain adequate hygiene standards.

Environmental Impact and Sustainability

Proper winery sanitation generates significant wastewater that requires appropriate treatment. Winery wastewater is produced in large volumes due to the need to sanitize facilities to maintain wine quality. This water is characterized by high organic content, acidic pH, and the presence of phenolic compounds that can be toxic if released into the environment without proper treatment.

The industry has been seeking more sustainable solutions. Nitrogen, for example, self-decomposes into oxygen without leaving residues, requiring no final rinsing and reducing the consumption of water and chemicals. Recent studies seek to optimize the concentrations and contact times of cleaning agents to minimize chemical inputs, aligning sanitary effectiveness with environmental responsibility.

Prevention versus Correction

Modern winery hygiene management philosophy is firmly based on prevention. As multiple studies demonstrate, it is substantially easier and more economical to prevent contamination than to correct it once it has taken hold. Brettanomyces perfectly exemplifies this principle: once established in barrels or other equipment, it is extremely difficult to eradicate.

Essential preventive measures include:

• Temperature management : maintaining the cellar at temperatures below 15°C significantly limits the growth of spoilage organisms.

• Sulfur dioxide control : maintaining adequate levels of molecular SO₂ is especially critical after malolactic fermentation.

• Minimizing cross-contamination : using dedicated equipment or a rigorous cleaning protocol between batches.

• Regular monitoring : test strips like Pro-Clean can quickly check for the presence of protein residue, while luminometers indicate the cleanliness of surfaces.

• Ongoing training : all staff must understand the critical importance of hygiene protocols.

An exceptional terroir, superior quality grapes, and masterful winemaking techniques can be completely compromised by failures in hygiene procedures. Conversely, exemplary hygiene practices will not create a great wine from mediocre raw material, but they are absolutely essential to allow the quality potential to fully manifest itself.

The evolution of the wine industry has seen remarkable advances in microbiological understanding, the development of more effective and sustainable cleaning agents, and the implementation of increasingly sophisticated monitoring systems. However, the foundation remains unchanged: daily discipline, meticulous attention to detail, and an unwavering commitment to sanitary excellence.

For producers who aspire to superior quality, the message is clear: investing in hygiene is not a cost, but a fundamental investment in long-term reputation and success. For consumers, understanding this invisible but crucial aspect of winemaking can deepen their appreciation of each bottle, recognizing the care and dedication that make the difference between a simply good wine and a truly exceptional one.

References:

• ADVID - Association for the Development of Viticulture in the Douro Region. (2021). Good Winery Practices Manual . PDR2020 - Rural Development Program.

• Christeyns Portugal. (2021). Hygiene in the wine industry .

• Dimopoulou, M., Longin, C., Halpin, B., Spann, B., & Masneuf-Pomarede, I. (2024). Critical areas for Brettanomyces bruxellensis contamination and biofilm formation in the cellar: On the origin of wine spoilage. OENO One

• Gabrielli, M., Fracassetti, D., Tirelli, A., & Demartin, M. (2021). Assessing the biofilm formation capacity of the wine spoilage yeast Brettanomyces bruxellensis through FTIR spectroscopy. Microorganisms , 9(3), 587.

• Le Montagner, P., Ballestra, P., Dols-Lafargue, M., & Masneuf-Pomarède, I. (2019). New advances on the Brettanomyces bruxellensis biofilm mode of life. International Journal of Food Microbiology , 318, 108464.

• Marchetti, M. G., Botondi, R., Guidi, F., & Savini, S. (2019). Minimizing the environmental impact of cleaning in winemaking industry by using ozone for cleaning-in-place (CIP) of wine bottling machine. Journal of Cleaner Production , 233, 582-589.

• Tristezza, M., Gerardi, C., Logrieco, A., & Grieco, F. (2019). Optimization of cleaning agents and best practices in a winery based on cleaning validation tests. BIO Web of Conferences , 12, 03008.

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WRITTEN BY:

Pedro Fernandes

Pedro Fernandes is a Portuguese winemaker who has been involved in viticulture since he was 11 years old, where he started making his first wines with his father and doing tasks such as pruning.

Since then he has never stopped and in 2018 he decided to dedicate himself to the wine sector, starting by doing "everything backwards". He began by taking wine specialization courses such as WSET (Direct Wine) and Wine Expertise (ISAG) in 2018/2019. Then he graduated from the University of Nebrijia in Madrid, obtaining an MBA in Oenology (2020). In 2021, at the age of 39, he decided to pursue a Bachelor's degree in Oenology (UTAD), and against all odds, he finished the course in 2024.

Along the way, he created his first personal wine brand - Chãos - and completed an internship at the prestigious Chateau Latour (in Bordeaux).

Currently, he works as a consultant in the wine sector, where he plays a role not only as an oenologist, but also in creating business strategies for wine producers, with a current vision of the market, which includes resources from Digital Marketing and Wine Tourism.