Tuesday, May 29, 2007

A study on vodka filtration

We've had a few comments recently on our vodka filtration process and how often we change our filter. For those just tuning in, all of our vodka infusion experiments make use of bottom-shelf Vladimir vodka, which we cycle through a Pur water filter to remove the impurities, a method developed by the scienticians at Oh My God It Burns!. Though others have repeated this experiment with mixed results, we find that by cycling the Vladimir through the filter five times, we can upgrade it to a fairly smooth and crisp middle-shelf equivalent (think Absolut, not Ketel One). Since any remaining impurity is usually masked well by our infusions, this is sufficient for our purposes.

We replace our filter on a monthly basis. At one infusion per week, Scottes from Scottes' Rum Pages rightly determined that we subject each filter to roughly 4 gallons of use (5 filtrations per infusion * 25.4oz per bottle * 4 infusions per month = 508 ounces). In contrast, Pur and Brita filters are rated for up to 40 gallons of tap water.

Keep in mind, however, that we also repeat some infusions to replenish our supplies. These repeat infusions are not always reported on the site. Though Wayland and I have cut back our drinking a bit since starting Infusions of Grandeur (gasp!), there are a few staple flavors we go through somewhat regularly. In addition, the practice of using some of our vodkae (particularly garlic and jalapeño) as a marinade has become somewhat common. I estimate that these repeats increase the filter usage to 6 or 8 gallons per month, depending on whether we throw a party in any given month.

This still seems to be a small amount, based on the filters' official ratings. However, we do notice a slight drop in quality as we approach the end of a month. In fact, we were overdue to change the filter during our disastrous second batch of strawberry, which may well have contributed to the unfortunate results.

Tap water filters contain activated carbon, which adsorbs impurities but does not bind to water or alcohol. (Note that adsorption is not the same as absorption.) Vladimir vodka is pretty vile stuff, and we presume it has a higher concentration of impurities than average tap water. As a result, the surface area of the activated carbon becomes saturated at a much faster rate.

If we were filtering a higher quality vodka, it is likely we could get nearly as much use from the filters as we might with tap water; but when using a low-quality vodka such as Vladimir (and that's when you really need the filter anyway), the filter must be replaced on a much more regular basis.

Addendum: I've been informed that the fine scienticians at MythBusters have attempted vodka filtration and declared it a myth. I haven't seen the episode in question, so I cannot evaluate the methodology they used. However, I can say from our experience at the Infusions lab that it does improve the quality of bad vodka to a tremendous extent. Again, however, it takes about five filtrations to do so, and it's still not top-shelf caliber.


annechen67 said...

Interesting that your strawberry infusion was the least forgiving. I have used over-ripe berries in melomel production (the term i was taught for "mead with fruit in") and gotten marvelous results, but the process is closer to jam-making than infusion. Thanks for the information on the filtering!

Mel said...

Thanks for all the info on the filters. Also, the Mythbusters thing *did* show that it improves the taste of vodka, though won't turn it into top-shelf. http://kwc.org/mythbusters/2006/04/episode_50_bullets_fired_up_vo.html

Scottes said...

Good analysis - as usual - on the filtering. As I mentioned before, I always change the filter when the filtering process slows down - as do you guys. Your comments about Vladimir having "higher concentration of impurities than average tap water" hit home. I'd hate to drink that stuff straight!

Keep up the good work guys!

Jimmy said...

Have you tested the pre/post alcohol content to verify it is the same?

Brendan said...

Unfortunately, our laboratory is not equipped with a hydrometer (yet), so we cannot determine the post-filtration alcohol content scientifically. Nor can we test it based on its intoxicating effects, because we're not willing to drink enough unfiltered Vladimir to get drunk. However, all of our research has assured us that ethyl alcohol passes through the activated carbon as easily as water. The carbon only binds to the solid impurities. Therefore, there is no reason that the filtered vodka would be a lower proof than unfiltered.

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