Ask Wine Wizard

Fun With Wine Filtration


John Cernac — Pueblo, Colorado asks,

I make a Cabernet/Merlot blend, 92-8%. I filter with a 2-micron filter before bottling and let it age three to four months or longer, but I have fine sediment in my bottles. What do I need to do to correct this problem?

The fun of filtration! I’ll deliver the bad news to you and my readers first by telling you that really no matter how tight of a pore size you use to filter your wines, there is always the possibility of sediment developing over time. In fact, with red wines, it’s actually just about guaranteed. You see, a lot of sediment we find in wines actually forms after the wine is bottled, and is nothing that filtration can control. Even if we pass the wine through a nominally “sterile” small pore filter size of 0.45 micron (through which the smallest bacteria cells cannot pass), over time phenolic substances can condense and fall out of solution, as may organic acids and other components. These all accumulate at the bottom of the bottle (or on the side, if that’s how you have it stored) as a fine sediment. In white wines, this is typically seen as the fine crystals of potassium tartrate, unless the wine was intentionally cold stabilized (chilled to force crystal formation and then filtered to remove the crystals) before bottling.
Response by Alison Crowe.