Determining Grape Fruit Maturity for Harvest
To make quality wine, it is crucial to know when to harvest. The following information details steps to sample, measure, and assess wine grapes for readiness. Use a grape maturity assessment form to record details each year.
Collect a separate sample for each block of grapes that will be harvested as a unit. A suggested sampling technique is to:
- Collect a sample of at least 100 berries to represent the block.
- Sample the berries from at least 20 clusters.
- Sample from the top, middle, and bottom of each cluster.
- Alternate between sampling from the East and West sides of the rows. Perform the instrumental measurements and the sensorial assessments from this sample.
Instrumental Measurements of Fruit Ripeness
Instrumental measurements of primary fruit chemistry for grapes usually consists of measuring the total soluble solids (in units of degrees Brix), total titratable acidity (in percentage or grams per 100ml), and pH. The must or expressed juice from a sample of berries is usually used for this evaluation.
Figure 1. Approximate target ranges for primary chemistry measurements of must at harvest (from Boulton, B., Vernon L. Singleton, Linda F. Bisson, and Ralph E. Kunkee. 1996. Principles and Practices of Winemaking. 1st ed. New York, NY: Chapman and Hall).
Sensorial Assessment of Ripeness
Do not rely on primary chemistry alone to tell you the ripeness of your fruit. Sensorial assessments and tasting berries can also tell us much about the development of flavor, varietal character, and phenolic maturity. Put the berries in your mouth and crush them, paying close attention to the flavors in the juice being released. Separate the seeds from the pulp and spit them into your hand for observation. Finally, crush the berry skin firmly between your rear molars and pay close attention to the degree of astringency, which is related to phenolic maturity.
Always pay attention to the appearance of new, desirable flavor components, as well as the disappearance of undesirable flavor components.
Use this Datasheet to record berry color, firmness, ripeness, seed color, overall acidity, and phenolic maturity of the cultivars in your vineyard. As you sample each harvesting block in your vineyard, take notes. By filling out this grape maturity assessment form, you will be able to maintain a detailed record of essential maturity components associated with the grapes in your vineyard. This will provide you with a helpful harvest reference, this year and years to come. Happy harvesting!