Harvest Time is Here Again

It is hard to believe, dear Brigade that a full year has passed since we last convened to discuss harvest.  The pleasant musing of callow youth and inexperience offered up romantic incantations to the wise, old farmer, squeezing a single berry betwixt a dirt-stained thumb and forefinger, proclaiming harvest time had come.  Harvest was ordained (cue trumpets and archangels), so we hopped the next Southwest flight to San Francisco to hand sort our fruit.  Apparently, I had it all wrong.  Now having completed the first two courses towards my UC Davis enology certificate, I’ve been taught the gauzy visions are just that, poetic garbage begging to be balanced by the cold, hard facts- numbers and data.  UC Davis tells us in no uncertain terms that “none of the flavor and aroma compounds [in the grape berries] are directly correlated with sugar and acidity (Bisson).”  In other words, one can’t reliably predict the amount of sugar and acid in a grape by taste test alone- you need to measure it. Many parameters can be used to assess berry ripeness, but the most common triad is °Brix, pH, and TA (“titratable acid”).  Degrees brix measures the soluble solids in the grape juice.  Even at its ripest, a grape is still 80% water by weight, but rounding out that last 20% is sugar.  Over the course of the growing season, the leaves hang out in the sunshine, working the spring and summer photosynthesis, generating sugar to transport to the fruit.  As the berries accumulate more and more sugar, they sweeten up until they’re ready for picking.  We can use a tool, called a hydrometer, to measure how much glucose and fructose resides inside the grape, and that value is the °Brix.  For red wines, harvest ready fruit ranges from 24-27 °Brix.  I give a range, since °Brix varies with temperature, vine location, sunlight, and across innumerable, individual vineyard practices.  The “right” number is also dictated by the desired wine style.  Even still, we can make some interesting generalizations about °Brix.  Usually, fruit with higher brix results in wine with more varietal character, which taste testers prefer in blind trials.  Ann Noble studied this.  She made 3 different Zinfandels: low, medium, and high alcohol wines, made from grapes with low, medium, and high °Brix.  Here is what she found.  In all rated attributes, the high alcohol wines from the ripest grapes were ranked first.  The highest alcohol wines manifest greater intensity of bitterness, berry and black pepper flavors, and greater viscosity.  Thus in Zinfandel wines, the flavor attributes that comprise varietal character are strongly correlated with sugar accumulation.  It would appear that more sugar=better wine, but first the caveats must be disclosed.  Grape berries don’t hoard sugar indefinitely; eventually berry sugar peaks, and then even drops.  By that point, you’ve missed the optimal window for harvest, and fruit quality declines.  As the fruit ripens, berry flavors transform from green vegetal tones into red fruit (strawberry, cranberry, apple) to black fruit (blackberry, plum, cassis) and finally to jammy date/raisin.  You’re aiming for the sweet spot, before it’s reduced to Gerber’s pureed prune.  Secondly, the more sugar in the berries, the harder the yeast must work to churn it into alcohol.  When the sugar is too high, sometimes the yeast hit the wall and just crap out.  They die, and you’re left with sweet dreck, which is not only stylistically unacceptable for our wine portfolio but also drastically increases the likelihood of bacterial spoilage.

The next two parameters are closely intertwined: pH and TA.  Both contribute to the tartness of the finished product, which gives the wine lively zestiness and focus, qualities of supreme importance when pairing wine with food.  Dear Brigade, acid is good.  Low acid wines are bland and flabby and age poorly.  Low acid wines are also more susceptible to microbial infestation and spoilage.  Grape berries begin their lives as small, hard, green acid balls- think sour patch kids.  Over summer, sugar increases and acid drops.  This is due to respiration (the berries metabolize their malic acid for energy) and dilution (the berries get bigger and acid is tamed by water).  In the real hot spots, like California’s Central Valley, the poor, scorching berries respire their malic acid a lot faster, so acid levels are much lower overall, and pH is higher.  These grapes have high sugar (from abundant sun) and low acid; they’re used to make bulk wine.  Generally, the increase in sugar parallels the rise in pH (as acid drops).  When we harvest our fruit, we like to see our acid (“TA”) at 7 ½- 8 g/L and pH=3.2-3.5.  There are even fancy formulas that try to combine the TA, pH, and brix into one equation to generate one optimal ripeness parameter, like brix x (pH)2 , brix/TA, and brix x pH.  Unfortunately, none perfectly or reliable predicts the optimal date for harvest.  They are simply more tools to help guide these decisions.  Compressing the complexity of berry ripeness into a single variable for selection/ prediction of an optimal harvest date is not only incredibly reductive but also inconclusive.  Consider for a moment an over cropped vine- one with too many uncontrolled berry clusters.  Since all of those berries will share the same finite amount of sugar, the amount of sugar per berry is low, but so it the acid.  Plug your numbers into the equation and the ratio is acceptable, but you’ll still make mediocre wine.  Or return to those Central Valley grapes.  “Optimal ripeness” is achieved well before the maximal °Brix, since the longer the berries hang on the vine, the more the acid drops.  You see, harvest is the final chain that ties viticulture to enology.  Once picked, you’ve sealed their fate.  The berries are delivered from the farmer to the enologist, with all of the fruity essence and flavor that ultimately shapes the finished wine.  While vintners can adjust acid levels and correct for defects in the laboratory, a grape deficient in berry flavors will never generate a berry flavored wine.  And while a farmer cannot control the weather or predict an onslaught of unwanted pests, harvest date can be selected and controlled. 

We had planned to pick the first of our Sonoma Coast grapes on 9/15.  Our numbers looked good, and the berries tasted ripe and fruity.  Unfortunately, fifteen hours of preharvest rain quelched that idea really fast.  A forecast for cool weather promised the brix would hold steady while the berries dried; harvest was delayed until 9/20.  On 9/16 we got word the block of 667 clone was green-lighted for 9/19 instead.  So we hand sorted our fruit yesterday.

We still have more pinot clones, and two other vineyards to go.  So the next time I show you something like this, you’ll know what I’m blathering about!  


2009 - Split Rock - Pinot Noir has updated harvest information-

Here are the most recent measurements taken from your vineyard block- Brix: 25.50 pH: 3.35 TA: 7.50


Works Cited

A. C. Noble and Mark Shannon Profiling Zinfandel Wines by Sensory and Chemical Analyses, Am. J. Enol. Vitic., Mar 1987; 38: 1 - 5.

 Bisson, L, Syllabus UC Davis Extension – Wine Production for Distance Learners, The Regents of the University of California 2005.