Testing the Chenin Blanc Grape Juice

The two bunches of Chenin Blanc grapes that I harvested for taking the Vital Statistics sat in the refrigerator for a few days. Then, I had an idea to take one more reading. First, I assembled the following: a ziplock bag into which I put the two clusters, a clean glass, and some pH strips that I had around for testing the pH of canned salsa.

First, I squashed as much of the juice out of the two bunches that I could and then I put the juice into the glass. I took the pH strip and dipped it into the juice and got the result that you see to the right.
The color is somewhere in between the first indicator, which is 2.8 and the second indicator which is 3.2. This is really not very precise at all but something that I could do. This juice has some acidity!
I then put the cup of juice into the refrigerator to simulate cold settling that we would do to settle out the grape solids. The juice turned a little brown in the refrigerator, indicating the conversion of caftaric acid, one of the most abundant phenolic compounds in white grapes, into the quinone form by the enzyme polyphenol oxidase (PPO).

Polyphenol oxidase is the same enzyme that turns a freshly cut apple brown. This reaction occurs in the presence of oxygen and can be beneficial in the process of making a white wine, although the presence of too much oxygen can lead to a process known as Hyperoxidation, and that process is not necessarily something that is desired in winemaking.
A close inspection of the photo on the right where the juice has turned brown, shows that the gross lees have indeed settled out. My husband and I tasted the juice and it was sweet with a punch of acidity. Our thoughts are turning to how to make wine from the 320 netted clusters in the vineyard. Stay tuned.