This is the last part of a 4 part series. Part 1 went over the importance of knowing when to harvest. Part 2 covered how to take the readings from the grapes and what they mean. Part 3 went over what kind of readings to expect.
What's One To Do?
Unless you have some high-dollar real estate in California wine country, it's not likely you will hit the best Brix, pH and TA readings all at the same time. Some years the climate will just not cooperate, and you will most likely need to make compromises.
Of course, you can get lucky in a particular year with just the right weather at the right time, but counting on getting lucky is a fool's bet. You must learn to make the best out of the meteorological cards you are being dealt.
A good rule of thumb is to try to harvest when the ratio of Brix to TA is between 31:1 and 34:1. This will always get you a good compromise between alcohol content and tartness.
As an example, lets say you do a titration and discover that the TA is .85--still a little high--and your refractometers Brix reading is 23. This gives you a Brix to TA ratio of about 27:1. You get this by taking the Brix and dividing it by the TA (23/.85). Not time to harvest.
Two weeks later you take another reading with your titration kit and get a TA of .73 and your refractometers reading says a Brix of 24. These readings get you a ratio of about 33:1. Time to harvest.
The only exception to this general rule has to do with pH. If the pH looks like it is going to go out of ideal range, then go ahead and harvest right away. This means for Whites, if it looks like it's going to go higher than of pH 3.3 then harvest. For Reds, if it goes higher than 3.5.
pH always trumps Brix and TA simply because you can't directly adjust pH later on without effecting the tartness of the wine, but you can directly adjust Brix and TA without effecting the pH too much.
The Gravity Hydrometer
In part one of this four part series I mentioned that a gravity hydrometer should be purchased, just as a way of double-checking your refractometers reading before actually harvesting the grapes.
So it's late in the season. You've been taking all your readings, and all the numbers have finely come into alignment, and you have come to the conclusion that its time to harvest. Stop! Now should be the time to take a reading with your hydrometer just as a means of making sure it is time to pick.
To do this you will need to crush up a couple of handfuls of grapes taken randomly throughout the vineyard and extract the juice. You need enough juice to get the hydrometer to float. A hydrometer jar is good in this regard because it is tall and slender and does not require a large amount of grape juice to get the gravity hydrometer off the bottom.
If your gravity hydrometer's reading matches your refractometers reading, then you're ready to harvest. Get to pickin' and crushin'.