By Erica Lundquist, Ph.D.
Former LCWC Viticulturist

To get an idea of what wineries are looking for at harvest I talked with several grower representatives. All of those I talked to were generous with their time, and I thank Frank Cabral of Sutter Homes, Skip Lovin of Kendall Jackson, and Jerry Quirk and Mike Snow of Beringer for their input on this Vineyard Note.

Because of a concern about hydrogen sulfide production in wines (causing a rotten egg smell), all of the wineries have guidelines for sulfur use. In general they want sulfur use cut-off by veraison. Fortunately, sugar contents are generally high enough by the end of veraison that powdery mildew control is no longer needed. By the time sugar content reaches 12-14% percent, old infections are inactive, and new infections of powdery mildew do not occur. Wettable or sprayable forms of sulfur may leave more sulfur residues than dusting sulfur, so some wineries request that the wettable forms be used only before bloom.

All of the winery representatives stressed the need to continue irrigation until very close to harvest, but not to overdo irrigation at the end of the season. Vines need water to continue photosynthesis, and therefore sugar production. Vines that are excessively drought stressed may defoliate and may have sunburned and dehydrated berries. Frequently dehydrated fruit will have undesirable, ‘cooked fruit’ flavors. On the other hand, excessive water availability tends to favor vegetative growth over fruit maturation, and the water may dilute the berry sugar content. Fruit from over-watered vines tends to have undesirable vegetative flavors.

Wineries are looking at several factors in determining when grapes are ready to harvest. Sugar content is often used as an indicator for when to monitor fruit maturity, however seed maturity is also important and fruit flavor is often the final determinant for the harvest date. Some wineries are monitoring juice components such as pH, titratable acidity and malic acid levels. Not surprisingly, wineries monitor all of these factors more closely in those vineyards they consider to have the highest quality fruit.

“Communication is key” was a common theme from the grower representatives. Informing wineries of problems as soon as they arise makes it possible to take corrective action in time for harvest. If growers are doing their own testing, wineries would like to know the results to back up the winery information. Scheduling deliveries and delays in deliveries are of course essential communication between growers and wineries. Almost like irrigation at the end of the season, growers need to be sure they do enough and timely communicating, but not to overdo it. Winery representatives are under tremendous time pressure at harvest.