A quick email to John Grazziano the winemaker at Millbrook informed me the berries in question are from heat stress / sunburn. In a week or so they will dry up without any impact on the other berries. He said "this happens every few years in our hot, good vintages." (So I guess that is a prelude of what is to come from the 2012 vintage providing the weather cooperates the next two months)
I did some research on grapes and sunburn. I found that some grapes are susceptible to high light, high temperature sunburn. When this happens, the pigment changes on the skin that results in yellow, bronze or brown lesions, often associated with a loss of chlorophyll.
Like everything else, I did find a sunscreen for grapes. But is it really necessary to spray chemicals to keep the canopy cooler?