Wine filtration

Filtration is a screen. Wine goes through; yeast, haze, and bits of grape do not (or not all of them). Clarification by settling or fining makes the load smaller. Filtration is the mechanical step. It is not Pressing wine (juice leaving skins) and not a moral upgrade of “unfiltered.”

TTB labeling treats treatment with filtering equipment — and fining or sterilizing agents — as cellar practice that need not change class, provided it does not rewrite the wine’s basic composition ¹. Silicon dioxide used as a clarifier must be completely removed by filtration; PVPP used to clarify must be removed during filtration ². So some authorized finings expect a filter after them. Bentonite lees are a solids problem; filtration is one way they leave ³.

Cross-flow is a direction, not a brand #

Among authorized processes, cross-flow filtration sends wine along a membrane under pressure. The fraction smaller than the pores is permeate (filtrate); everything else stays as retentate ⁴. Ultrafiltration is listed to remove proteinaceous material from wine, to reduce harsh tannic material from white wine made from white grapes, to pull pink from blanc de noirs, to split color fractions, and to reduce alcohol — with membranes selective for molecules greater than 500 and less than 25,000 molecular weight, transmembrane pressure under 200 psi, and vinous character left intact ⁴. That protein job is the same haze family as Protein on the fining page. Reducing tannin is a structure choice; Smith still describes astringency as saliva-protein binding in what remains ⁵.

Reverse osmosis in this table is a wine process (alcohol reduction, off-flavor removal) with tighter molecular-weight and pressure limits — not the pickle-brine Osmosis process, though both use membranes and dissolved material. Nanofiltration is listed with volatile acidity and alcohol uses. Dealcoholization processes in that section have extra premises rules and plant-specific details ⁴. Sterile-filter ratings likewise depend on the membrane and the producer’s target.

Lees are what you are often trying not to bottle. Sulfur dioxide is a different microbial and oxidation lever; a filter is not a substitute for it.

What to notice #

Look: wine that was dull goes lamp-bright; a filter that blinds (flow dies) is overloaded colloids, not a virtue. Taste: a thinner, stripped wine after a tight pass is over-filtration. Smell: cardboard or hollow fruit is the same failure. Unfiltered wine can be stable if protein and microbes were handled another way; cloudy wine in the glass is a style only if it was meant — protein haze after a warm shipping day is not ³.

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