Filtering–To Be or Not To Be (May 3, 2010)

Easily one of the hardest mental jobs in the winery is filtering.  It should be simple.  Choose the right courseness of filter pads, the right number of pads for the volume of wine, and go.  The reality is that even with all the turbidity (cloudiness and solids in the wines) information we have, it is not an exact science.  And if you get it wrong, the filter plugs up before the wine’s finished, and you’ve just added on a boatload more work.

Here are the nuts and bolts of filtering.  First of all, we filter most of the wines (the Single Vineyard wines (Black Label) are the exception) for stability.  Filtering allows us to pretty much guarantee that the wine won’t referment in the bottle or let other less desirable microbes bloom, thus producing off-flavors. And all this within the context of how the wine is stored (i.e.  the store shelf versus your private humidity and temperature-controlled wine cellar).  It’s insurance that aging the wine in a wide variety of circumstances will still give a great experience.

It takes me three hours to sterilize the equipment for filtering.   I can filter approximately 400 gallons an hour, if I’ve chosen the filter pads correctly.  But remember, the more times you filter or the more pads you use, the greater the chance for negatively impacting the quality of the wine.  So, it’s a fine line of trying to choose the right number of pads, not too many, but enough to finish so you don’t have to do it all again (and potentially screw up the wine).  See the potential stress?

Over the years I’ve gotten pretty good and choosing the right combination of pads and filtrations to retain the elegance, fruit and balance in the wines.  The experience hasn’t been without very long days (finishing at 2am, with the filter plugging (letting through only 14 gallons/hour), but it has been educational.

And until today, I thought I had this whole thing under control.  But the 2008 Cabernet Franc has thrown me for a loop.  I filtered it through a set of 3 micron pads and then a set of 0.8 micron pads.  Normally, this would be a good bet for sterile filtering the wine on the bottling line (through a 0.65 micron membrane).  The filtrations went well, and we bottled today.  But there is something that is larger than 0.65 micron and smaller than 0.8 micron in the wine that totally plugged up my bottling membrane filter.  So I had my crew of 6 standing around while I figured out how I plugged a $300 membrane filter.  I still don’t know, but it means putting another filter inline on the bottling line tomorrow, and crossing our fingers.

Even with all this, the extra work, the extra time, the extra money, etc., the one saving grace is that the wine is tasting fantastic.  And that makes it worth while.

Filtering’s complicated, and I hope this long-winded explanation helps a little (even though it touches just the tip of the iceberg).  May my next filtration go smoothly, and please don’t hesitate to ask questions in the tasting room when you see me.  I’ll definitely talk your ear off about the romantics nights alone waiting for the filtration to finish!

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