How to Ensure Wines are Microbially Stable.

For packaged wine to be successfully bottled, it must be microbiologically stable, visually clear, and free of particulates. Let's explore the three stages of filtration that take place in the winery before wine reaches your glass.

Coarse Filtration

This initial clarification step occurs after fermentation when the wine is cloudy but translucent. The aim is to remove larger particles, such as yeast cells, tartaric acid crystals, or wine fining agents. Traditionally, diatomaceous earth filtration or filter sheets were used, but advancements now include lenticular/stacked disc solutions, cross-flow filtration, and cartridge filtration.

Standardisation During Coarse Filtration

The standardisation or pre-stabilisation process addresses microbial stabilisation, clarity, and potential filter blockage before final packaging. This step ensures stability during transport, protects the wine’s essential characteristics, and reduces the levels of sulfur dioxide required.

Filterability Index (FI) Testing

Packaging facilities often perform Filterability Index (FI) testing to assess the wine’s filter-blocking potential before offloading it from road tankers. FI testing involves passing wine through a 0.45μm filter disc at 2 barg pressure, measuring filtration times for 200ml and 400ml. A low FI value (<20) indicates low blocking potential, while a high FI value (>20) signals likely blockage issues.

Why It Matters

Coarse filtration safeguards the wine’s quality by removing particulates and setting the foundation for subsequent filtration stages. This step is crucial in ensuring wine stability and maintaining its sensory appeal.

Fine Filtration

At this stage, the wine is clear and bright. The focus is on reducing yeasts and bacteria while preparing the wine for sterile filtration.

Key Benefits of Fine Filtration: 

1. Clarity Enhancement: Fine filtration achieves the brilliance and clarity that enhances the wine’s visual appeal.
2. Prefilters for Particle Retention: Prefilters capture fine particulate matter and protect final membrane filters. While polypropylene (PP) filters work well for particle retention, glass fibre (GF) filters are often preferred due to their natural charge and finer fibre diameters, extending membrane filter life.
3. Microbial Retention: In some cases, prefilters also demonstrate microbial retention, ensuring additional protection for the wine.

Fine filtration is about more than achieving clarity; it is essential for protecting the wine’s integrity and enhancing its quality. Proper prefiltration ensures cost-efficient and reliable filtration processes, preparing the wine for the final step.

Sterile Filtration

The final stage of filtration ensures microbial stability just before bottling. Membrane filtration securely removes spoilage organisms that could cause turbidity, off-flavours, or microbiological issues post-bottling.

Red vs. White Wine Filtration

• Red Wine: Naturally higher tannin levels and lower sugar content make it less susceptible to microbial contamination. A 0.65μm membrane filter is typically sufficient.
• White Wine: Due to higher contamination risks, a finer 0.45μm membrane filter is recommended.

Validation and Integrity Testing

Membrane filters must:

• Retain spoilage organisms (e.g., Saccharomyces, Brettanomyces, Acetobacter, Oenococcus).
• Preserve wine characteristics such as sweetness, acidity, tannin, alcohol, and body.
• Be integrity testable and compatible with chemical sanitisation, hot water, or steam sterilisation.

Filters are typically made from PES, PVDF, or Nylon, ensuring durability, reliability, and high flow rates for efficient operations.

Why It’s Important

Sterile filtration not only ensures microbial stability but also safeguards the sensory qualities of the wine. This step guarantees the highest product quality and safety before the wine reaches the bottle.

For further information on wine filtration solutions, feel free to contact our experts. You can give us a call or send us an email - we're here to help you make the best choice for your filtration needs.

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