Wednesday, November 14, 2012

Wine Faults--a fascinating seminar

I've been silent for a while, so apologies for that.  Been busy getting architects & contractors lined up to build the winery this winter.  Still not done (waiting on the architect's final plan), but I've managed to fit in a few "continuing education" experiences.  A very interesting seminar was a "wine faults" class held by the MA Farm Winery & Growers Association.  Certainly we all hope that our wine smells wonderful, but on occasion, nature throws a curve ball and we have to be able to detect off-flavors that reduce the wine value or indicate even bigger future headaches.

"Know Your Faults: A Sensory Evaluation of Wine Flaws"
Presented by Chris Gerling & Anna Katharine Mansfield from the Cornell Univeristy Enology Department.

I had actually attended a short version of this class at the Winemaker Magazine Conference earlier this year and really enjoyed it.  I went with high hopes that the full day class would be even more educational--and I was rewarded.

Now usually, I enjoy going to wine education events because you get to taste wine in the name of education, but this was the first time that I got up at 6 AM to drive 1.5 hours and spend the day evaluating bad wine!  We had 8 flights of wine that had been doctored with the chemical components responsible for the bad or unpleasant aromas in wine.

Flight 1:  Sorbate-Related Flaws in White Wine
     Sorbic acid is used to prevent re-fermentation activity in sweet wines, but ~50% of people can detect the presence of the potassium sorbate used to introduce sorbic acid to the wine.  In addition, sorbic acid eventually gets esterified by the ethanol in the wine to form ethyl sorbate, which gives a bubble-gum fruitiness to the wine.  Tolerable in fruity white wines, but not a good thing in sweet red wines.

     I learned that I'm one of the minority that can not detect ethyl sorbate.  Smells like wine to me!

Flight 2:  Oxidation in White Wine
     We had a glass of oxidized wine and 2 glasses of with low and high levels of added acetaldehyde

Flight 3:  Sulfur Dioxide (SO2) in White Wine
     Three glasses of low, medium, and high levels of free SO2.  The levels they gave us may have been over-calculated because the low level stung my nose, the medium made me gasp for air, and I couldn't even get close to the high level glass!

Flight 4:  Volatile Acidity in White Wine
     Volatile acidity is detected as a mixture of acetic acid (AcOH) and ethyl acetate (EtOAc from esterification of acetic acid and ethanol).  The low level glass was a mixture of 800 ppm AcOH/100 ppm EtOAc.  The medium glass was a mix of 1000 ppm AcOH/250 ppm EtOAc, while the high glass was 1200 ppm AcOH/500 ppm EtOAc.

     Interestingly the low level glass was immediately identifiable as vinegar (AcOH), while the medium glass was more pronounced EtOAc.  But the high level glass was pure vinegar to my nose.

Flight 5:  Trichloroanisol (TCA) in White Wine
     Low, medium, & high levels of TCA, which is the cause of "cork taint".  When fungi in the cork or other wood products in the winery come in contact with sources of chlorine (bleach or other sanitizers), they produce 2,4,6-trichloroanisol (TCA) that smells like musty cardboard at extremely low levels (3 ppt).

    This was immediately identifiable even at the low level.

Flight 6:  Sulfur Compounds in White Wine
     One glass of a high level of hydrogen sulfide (H2S) that was gagging and overpowering.
     A low & high level of dimethyl sulfide (Me2S or DMS).

     The H2S glass was simply over-doped with an overpowering smell of sewer gas.
     DMS at low levels can add earthiness or flavors like creamed corn or truffle to a wine.  At high levels, it's just rank!  These 2 glasses were simply rank to my nose.

Flight 7:  Volatile Acidity in Red Wine
     A repeat of Flight 4, but in a red wine.  Interestingly the low and medium level glasses in this flight smelled more like fingernail polish instead of vinegar, but the high level was unmistakenly vinegar.

Flight 8:  Brettanomyces in Red Wine
     This was an interesting flight.  Brett is a yeast that is usually always present in a winery.  If low levels of SO2 allow brett to flourish, then it can produce off-flavors.  At low levels, these aromas can add complexity to a wine (mushroom, forest floor, earthiness--this French wine!), but high levels result in reduced fruit flavors or added descriptors like "band-aid, burnt match, horse blanket, manure, or rubber"--not the most pleasant of smells.  :)

     Since there is no one compound solely responsible for brett-related off-aromas, the folks at Cornell have come up with a cocktail of 4 compounds that most closely replicate brett aromas:  4-ethylphenol, 4-ethylguaiacol, isovaleric acid, and guaiacol.  In this case, the low level glass smelled like a smokey campfire & mulberries.  The medium level glass tended towards band-aid, but with an interesting clove aroma.  The high level glass just smelled like strong band-aid with a sweet vinegar note. 

All in all, a very interesting class.  I thought the glass examples were a little outside of the normal levels encountered in commercial wines, but they did provide a strong signpost for future reference.  I'm pretty happy to say that these are not aromas that I have encountered in my wines, which means I'm doing something right!

The 3 best ways to avoid all of the flaws above:
1) Sanitation
2) Keep tanks/carboys/barrels topped off
3) Maintain SO2 levels


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