Types of Filtration
- Coarse filtration (pad/sheet) — removes larger particles using cellulose pads of varying porosity. Used for initial clarification after racking
- Membrane (sterile) filtration — passes wine through a 0.45-micron membrane that removes virtually all yeast and bacteria. Ensures microbiological stability before bottling
- Cross-flow filtration — wine flows tangentially across a membrane, reducing clogging and allowing continuous processing. Increasingly popular in modern wineries
- Diatomaceous earth (DE) — wine passes through a layer of fossilised algae that traps particles. Traditional and effective but being replaced by newer methods
The Filtration Debate
The question of whether to filter is one of the most contentious in modern winemaking:
- Pro-filtration — ensures visual clarity (consumers expect bright wines), prevents refermentation in bottle, removes potential spoilage organisms, and guarantees stability for shipping and storage
- Anti-filtration — natural winemakers and many premium estates argue that filtration removes beneficial colloids, colour compounds, and aromatic molecules that contribute to mouthfeel and complexity. Many top Burgundy, Barolo, and Rhône producers bottle unfiltered
Unfined and Unfiltered Wines
Wines labelled "unfined and unfiltered" have undergone neither fining (protein removal) nor filtration. They may appear hazy or throw sediment, which is harmless. This approach has become a badge of artisanal quality in the natural wine movement, though it requires impeccable hygiene and healthy grapes to avoid microbial issues.