Prevent Nightmare Bottling Days with Filterability Testing
Last Updated: 3/2023
Applies to: wineries that have filtered their wine prior to bottling day and are using an in-line sterile membrane as the final filter before the bottling line.
A clogged membrane filter can bring bottling to a halt, causing costly and frustrating delays. Even if wine has been filtered (pad, lenticular, crossflow), it may still clog the membrane filter on bottling day. Read on to learn more about how filterability testing can save you from unnecessary headaches.
What causes membrane filters to clog?
There are two main types of compounds in wine that can clog membrane filters:
- Particulate matter and suspended solids: large, often visible compounds including tartrate crystals, polyphenolic precipitates, microbial hazes etc.
- Colloids: small complexes formed when particles in wine are assembled by intermolecular forces. These compounds include those naturally present in wine like polysaccharides, proteins, mannoproteins, and phenolics, as well as fining agents like carboxymethylcellulose (CMC) or gum arabic.
Particulate matter/suspended solids are often effectively removed by pad filtration, lenticular filtration, or crossflow filtration. Colloids, on the other hand, may not be removed (or may be distrupted) by these types of filtration and can be difficult to identify and quantify. For this reason, they are usually the main cause of a clogged membrane filter on bottling day.
What is filterability testing and how can it help?
Filterability testing is a simple way to identify wines that have the potential to clog membrane filters. Filterability testing can be run in-house with specialized equipment or can be sent out to external laboratories like ETS. Testing should be conducted as close as possible to bottling.
Filterability testing uses a sample of the wine that will be bottled in conjunction with the same membrane material that will be used in the final filter. A sample of wine is pressurized as it passes through a 25 mm membrane filter disc (provided by the manufacturer and made of the same material as the membrane filter). The test measures the weight of wine filtered (grams) over time (seconds) and returns a filterability index value.
Interpreting the results:
- If FI > 20, filtration problems may occur
- If FI ≤ 20, no filtration problems are expected
- If FI ≈ FIm and ≤ 20, no filtration problems are expected
- If FI << FIm, filtration problems may occur, especially as filtration progresses
- If FI >> FIm and ≤ 20, no filtration problems are expected
Note: filterability testing is not fully representative of what happens on the packaging line, and filtration can be impacted by factors such as the volume of wine to be filtered, membrane and pre-membrane condition, etc. For example, extremely large volumes of wine with moderate FI measurements could still clog membranes.
Beware of turbidity measurements as a tool to predict filterability
Turbidity is a measurement of light scattering and provides a rough estimate of particles in the sample that are large enough to deflect light (particulate matter and suspended solids). High turbidity can indicate that a wine will clog a membrane filter. However, turbidity does not measure complexes that are too small to deflect light, including many colloids that can still clog membranes. Therefore, turbidity should not be relied upon alone to determine filterability. Filterability testing is the only way to assess whether both particulate matter and colloids in a given wine will clog the membrane filter
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