Controlling Runaway Sugars & Harvest Date With Irrigation

At times I feel like an airplane captain charged with bringing this commercial flight in with the smoothest possible landing, especially after last year's fiasco when it was more like a jet fighter landing on an aircraft carrier at night slamming down the tail hook and almost skidding off the deck. I had already made an announcement to the passengers that this was the last chance to get up and stretch their legs as we would soon be preparing for landing (while our pilot friends in Napa Valley, far to the north of here, are just getting round to serving cocktails on their flight). The weather turned warm 9 days ago and as expected the sugars in the then purple grapes began to rise. It was time to check how much. I took a representative sample of 20 berries from each block measuring the juice with a refractometer. The results (as of 8 p.m. Aug. 20):

Tempranillo: 19.5 brix
Zinfandel: 21.5 brix
Petit Sirah: 16.0 brix

The shocker was the Zin, because the Tempranillo started and finished veraison before the Zin, and I was planning to harvest the Tempranillo first. In addition, I've been consistently irrigating the Zin with more water this year than last (when a heat wave struck this time last year sending the Zin sugars to 28 brix while the acid was still high).

I tasted the Zin grape juice, and sure enough, my mouth puckered at the tartness and extremely high acid. "Ladies and gentlemen this is the Captain. The good news is we're ahead of schedule, but on the ground there's a plane stuck in our gate. Air Traffic Control has put the Zin flight into a holding pattern." In other words, we're turning up the water (or in this case, planning to give it its normal irrigation). So, this morning (Aug 21) I watered the Tempranillo and Petit Sirah for 45 minutes (except for the 2 longest and most fruitful rows of PS which got none); the Grenache for 1 hour and the Zin for 2 hours.

If you're concerned about our precious water resources, the Blue-Merle's water usage in July was 43 HCF (31% less than our allocation) with a cost of $157 for 1,150 vines plus alpha (alpha being the "family fruit trees" avocados, macadamias, olives, figs, peaches, oranges, tangelos, lemons, limes, persimmons, kumquats, pomplemousse, etc. and the 47 Canary Island Palm trees the Queen purchased with our last savings at the start of the recession which are now worth more than our house).

For the record, the small block of Durif (aka Petit Sirah) vines at the bottom of the hill are done: the sugars taste perfect, the berries are wrinkled. These are always the first to budbreak in the Spring and the first to ripen. We'll let them go ... it's only a couple of gallons of juice at most and at harvest their over-ripeness will contribute rich flavors to the overall Petit Sirah harvest.

Seasonal warm weather is forecast for the next week with the Tempranillo and Petit Sirah flights preparing for smooth landings in September. I wonder how turbulent the Zinfandel approach will be and if the Captain's actions will deliver a harvest with perfect sugars, acid and pH?

Update as of August 28th:

Zinfandel: 23 brix; pH=3.15; TA = 1.35
Tempranillo: 22 brix; pH=3.6; TA = .94

Watered Zin last Saturday (full watering, about 1.5 hrs) and Tempranillo (about 45 minutes); watered Zin again on Tuesday in middle of heat wave; watered Zin today (Sat. 8/28) for one hour. No water for Tempranillo. Temperatures of turned seasonably cool today for end of August. Let's see what next week brings.) Here we are, watering a drought resistant plant, in order to control sugars and ripening. This is why we're wine growers, not grape growers.