What kind of parents are grapevines? (Or, do higher yields mean lower quality?)

Nov 10, 2014

(PalatePress) - Last November, a pair of American economists published a working paper with the National Bureau of Economic Research stating that first children earn higher grades than kids born into more crowded families. Asking questions about family size and child success is dangerous. Bring it up in a crowded room and you’ll hear that only children are antisocial or deprived, that kids with lots of siblings don’t get enough parental attention, that first children are bossy, that first children are statistically likely to be more successful than children at the bottom of the stack, that children from big families have fewer psychological issues later in life…

 

Start asking the same questions about what kind of parents grapevines are and the barrage is just about as bad. Does a high-bearing vine with lots of clusters feed and shelter each of them just as well as one with fewer clusters? Or are grapes from low-yielding vines naturally higher in quality, like straight-A-earning only children? Like the only child/big family debate, we have statistical data. Like the only child-big family debate, the data aren’t always the last word.

Grape yield isn’t directly related to wine quality. Lower yields often do mean higher quality, but that’s not because one causes the other. It’s possible, given a whole lot of other factors, for high-quality grapes to come in big lots or in small ones. But grape yield is indirectly related to wine quality; in other words, our data say that a lot of factors often associated with yield affect quality.

Because contemporary science works on the principle of falsifiability – find one exception to the rule and you throw the rule out the window – it’s easy to throw out “lower yields mean higher quality.” A very well-respected 2004 article demonstrated that wines from heavily-pruned, low-yielding Napa cabernet sauvignon vines were more vegetal, astringent, bitter, and less pleasantly fruity than their higher-yielding counterparts. Other research has shown that lower-vigor, lower-yielding sauvignon blanc vines can have less punchy varietal flavor. And combinations of vigorous vines, lots of water, and the wrong kind of trellising can mean low-ish yields of low-ish quality fruit. So we’ve proven that principle false.

Overcropping is clearly bad. Vines have a sugar checkbook. Leaves exposed to good, plant-nourishing sunlight bring sugar in with photosynthesis; grapes are sugar storage units, like savings accounts for carbohydrates. If a vine has too few sugar generating units for its sugar storage units, those savings accounts won’t fill up very fast and grapes may not ripen to a winemaker’s specifications. But every wine drinker knows that quality isn’t just about sugars and alcohol. You can’t measure how well kids turn out just by looking at their high school grade point averages.

"Without a way to process sunlight, you won't see sugar ripening," he said. Imagine that: a warm, dry California summer leading to underripe grapes.


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