I just talked to a friend of a friend vintner. She is relatively small
commercial production and in the middle of her own crush. She said all
the Napa fruit is coming in with very low TA levels this year due to
the really high temps and super wet spring. She has had a 25 lb bag to
tartaric she's been working with for 4 years now, but used it up and is
almost through another 25 lb bag so far this year and she is still
crushing. I guess that makes me feel a bit better, I'll wait a few
days and maybe add 1/4 lb or so tartaric and check pH and TA again.
She said a quick back of envelope calculation would add about 1/2 lb
total, but also said to be really careful of pH and not let that go
below 3.4 to insure ML fermentation.