To Filter or Not?

To date, with the few wine kits I have made, I have never filtered the wine before bottling.  Most of the wine kit instructions recommend filtering because it supposedly enhances the clarity of the wine, and removes some of the residual yeast cells that are still floating around.  With my valpolicella kit, the store gave me a coupon for a half day filter rental, so I decided to go ahead and try filtering this wine before bottling.  The store gave me a "Buon Vino Mini Jet" electric filter for the afternoon:  http://www.buonvino.com/minijet.html

The wine filter consisted of a pump connected to an arrangement of plates that force the wine to pass through a sequence of three filter pads, and then through an outlet to a long piece of tubing that carries the wine to a carboy for storage until bottling. The edges of the filter pads are exposed, which allows some wine to escape.  This is probably good for the pump, because if the filter pads get clogged, wine can escape through the sides, which prevents the pressure from building up.  Any overflow wine is collected in a drip tray which drains to a holding container via a length of tubing.

My valpolicella wine had been sitting for some time after clarification, and there was an inch of precipitate at the bottom of the carboy.  So, before starting, I racked the wine into a clean carboy.  This way, I didn't have to worry about the fine solids clogging up the filter pads.  I noticed that the racked wine was already pretty clear.

After the somewhat fussy process of sterilizing the pump and tubing, rinsing with cold water, and flushing water through the filter pads, I began filtering.  I was pleased with the filtration rate, which was a lot faster than what I usually get when I siphon wine from one container to another.  When the carboy of unfiltered wine was empty, I filtered the two litres of overflow wine.

The filtered wine was 'agitated'.  That is, there was a fine foam on the surface, which is meant to be the result of carbon dioxide out-gassing from all the mechanical agitation that happens during filtration.  It took a few hours for the foam to disappear.  As per the instructions, prior to bottling, I let the filtered wine stand overnight in a carboy fitted with an airlock.

Bottling was uneventful, and a sample of the wine tasted much like it did when I first tested it.

30 bottles of filtered Valpolicella

So, was filtration worth the effort?   Filtration seems like a really good way to degas the wine if there is any excess carbon dioxide or sulfur dioxide present.  It is probably a good way to remove any of the finings that are left in the wine after racking, but this only applies to instances of sloppy racking.  If you are careful with racking, your wine should be very clear and may not even need to be filtered.

I personally found it to be a fussy process that creates a number of opportunities to contaminate the wine (e.g. sterilizing and rinsing the wine filter is not easy because of all the little grooves and small parts).  Plus, the whole process is clearly a very good way to aerate the wine: the wine is squeezed through filter pads with high surface area (in air); the overflow wine sits in an open drip tray before flowing into an overflow container; the filtered wine flows at a high rate from the outlet tubing, and this created a sort of waterfall effect in the final carboy, mixing up the wine with lots of little air bubbles.  Basically, there was a lot of aeration.

Would I do this again?  On balance, probably not.