Vineyard Management The art and science of grape harvest


Knowing when to pick means paying close attention to visual clues and flavours. By Gary Strachan


I


guess the easiest way to find out when to pick is to wait until the winemaker who is buying your grapes says it’s time to pick. On the other hand, perhaps you might be both the grower and winemaker, and you could be losing sleep over the conflicts between wanting to harvest the crop right now and wanting to make the best possible wine.


Once upon a time we used to make the decision completely on sugar content. Many varieties were cropped quite heavily and if we could pass 20 degrees Brix, we called in the pickers. There were lots of conflicts about flavours and composition and eventually the industry started to pay more attention to pH and titratable acidity (TA).


There was a pretty good chance that if the Brix and pH were a little bit higher and the TA was a little bit lower that a decent wine could be made without the aid of sugar and acidex. But that was long ago. We now know that grapes go through a hierarchy of flavour changes during the last few weeks of maturation. Flavour changes are only loosely related to the traditional analytical variables of sweetness and acidity. We also use visual cues and flavours, especially flavours.


I learned this lesson during a “light bulb” moment over 20 years ago. In the B.C. grape and wine industry we had been searching for a composition standard that could be used as a basis for grower bonuses. During a seminar, one of the top California winemakers said he had examined all of these variables and given them up. He said the only provision in his grower contracts was “You pick when I tell you to.” It wasn’t arrogance. It was a practical recognition there is no universal composition that will assure the presence of optimal flavour in


grapes.


The first level of assessment are the visual cues. When grape vines reach fruit maturity they also start hardening off for winter. The lowest leaves on each cane become pale and then yellow. The canes turn brown at the base and then the lignification gradually moves upward along the canes.


There is a threshold composition that should be attained for any given style of wine. For example, lighter styles of wine benefit from being harvested before the sugar is higher than, say, 22 Brix. In order to safeguard the fruity flavours, it is also beneficial to harvest while the pH is still at a moderate level, of, say, under 3.5.


Don’t forget that analytical variables are a continuous function, thus there is no hard endpoint beyond which you must not go. Within these limits of composition, there can still be wide variation in flavour, dependent on vine


British Columbia FRUIT GROWER • Fall 2012


The fresh fruit portion of the wine aroma wheel. Oxidized and fully mature flavours increase in the


lower portion of this list. With permission, Ann Noble, University of California, Davis."


vigour, variety, and the balance of vegetation to crop level.


Flavour development in grapes follows an interesting sequence. Depending on the variety, the typical pre-harvest flavours are vegetal, typically described as grassy, asparagus, or bell pepper. From there the flavours evolve according to whether the grapes are red or white. Red varieties tend toward red berry flavours and white varieties tend toward tree fruit or white berry flavours. As berries mature, they follow the groups presented on the flavour wheel on the outside tier between noon and six o’clock.


As you move downward on the 21


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