How to Test When Wine Grapes Are Ripe

Select a sample of grapes. Choose grapes with deep coloring, loose, but not wrinkled skin, which release easily from the stem. Pick grapes from the top, bottom and middle of each row, selecting a grape from each bunch.

Place the grapes into a piece of cheesecloth held over a bowl.

Bring the edges of the cheesecloth together to create a pouch. Twist the pouch and squeeze it between your hands to extract the sample of juice.

Lower the cheesecloth bundle with the grapes into the bowl, leaving the cheesecloth closed. Set the sample at room temperature for two hours to settle the sediment.

Remove the cheesecloth bundle and insert a thermometer into the juice. Test juice ideally as close to 68 degrees Fahrenheit.

Place the hydrometer into the grape juice and take a reading of the degrees Brix. Ripe grapes should be less than 24 degrees Brix.

Follow the directions included with your pH test kit to determine the tiratable acidity and acidity. Generally, it will require you to add a couple of drops into a container. Then, you will use a specially-treated paper that will yield a specific color indicative of the acidity levels. Ready to harvest grapes should have a tiratable acidity value between 0.58 and 0.64 and a pH level between 3.4 and 3.6.