Monday, September 5, 2011

Book Report -- Wine Faults: Causes, Effects, Cures

John Hudelson holds a PhD in Chemistry and has worked for decades in the wine industry.  He created this book from a PowerPoint presentation for wine judges on the difference between a flaw and a fault, but it grew bigger, eventaully becoming a very complete list indeed.

This book is not for the afficianado of wine.  It isn't for sommeliers, or most students.  It is for people with several chemistry classes under their belt who are going to make a living by making wine.  Parts of it are completely impenetrable and had me going to Wiki multiple times, and I still don't understand it!

For example, there are several chemical compounds in wine that can cause or speed up the production of volatile sulfur compounds (bad) in the absence of oxygen.  That is important because most winemakers are trying to avoid introducing oxygen into winemaking.  But there is a chart of half-reactions with their 'redox' potential expresed in volts.  It took a trip to Wiki to figure out why he is listing half-reactions and why that stuff is expressed in volts to begin with; and I never could fathom if the scale was useful or how common any of those reactions are.  Frustrating.

My big takeaway from this book is an appreciation of how complicated the winemaker's process can be.  I used to think of it as a tightrope act between, say, acid and flab, tannin and lack of structure, fruit and barrel characteristics, etc.  But it's more of a dance on a tightrope.  For example, when you start fermentation, every strain of yeast you might select works best under different conditions, conditions you cannot necessarily control.  If it's out of its sweet spot, that yeast will start producing nasty byproducts.  If it is in its sweet spot, it still might produce nasty flavors depending on all sorts of chemical factors.  So dance, motherf*%ker, and remember that nitrogen is bad in the vineyard, but vital in the fermentation tank!

Hudelson also does a great job explaining two issues in winemaking that have been eluding me, the issue of volatile acidity and the play between total acidity and pH.

Total acid is the measure all all the fixed (not volatile) acid in a wine. pH is the measure of the strength of thse acids. We don't really taste the power of acids as much as how much is there, so TA is important. A wine with 5 grams per liter of acid is fat and flabby, and at 9 grams per liter it is very sharp. pH is important for the stability of wine. 4.0 is very unstable and 3.0 is very stable.

Volatile Acidity is acid that is in gasseous form at room temperature.  All wine has a bit as a byproduct of fermentation, usually below the threshold of human perception (700mg/l).  It can seem like consumers are detecting more and more, but that isn't necessarily true.  Screwcaps and other modern closures are preventing VA from exchanging out of the wine as they would in semi-permeable cork.  So just decant or swish your glass and it'll go away.  In my classes, VA got caught up in conversations of sulfur compounds that smell similar and are indeed on the rise.  Also VA can convert to vinegar.

Consider that a pH falls, production of VA in the form of acetic acid rises.  If a high level of alcohol is present, that will convert to ethyl acetate...vinegar.  Lots of new world wines love the profile of low acids because they want a generous rich wine.  They are also picking their grapes later and later to get the most color and fruit flavors.  But picking late means more sugars which translate to more alcohol - vinegar city.

Hudelson also tells us how to get rid of vinegar precursors, but that is really really esoteric, and I think you get the idea.  Lots of information, much of it not useful to all but the hardcore.

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