How Ripe Are My Grapes?

Or,

"How do I know when to pick my grapes?"

There are many aspects of grape maturity that are available to the grower to be taken into account to determine the best time to harvest wine grapes. Some of these a quantitative and can be determined to a high degree of numerical accuracy, and others are qualitative and are more subjective.

Qualitative indicators of grape maturity include color of the skins, stems and seeds, appearance of the vine and leaves. Current and expected weather conditions play a large roll in weighing the decision to pick today or let them mature a bit longer.

Quantitative indicators include measurements of the actual chemistry of the grape itself. These include, but are not limited to, sugar content (brix), pH, and titratable acid (sometimes referred to as total acid).

This page focuses on the quantitative measures and uses applies some simple rules or guidelines that can be used to give an indication of both grape maturity and, more importantly, indications of appropriateness for the current harvest to making the type of wine the vintner chooses.

Reading Brix pH TA (g/l) Date(mm/dd/yyyy) Notes
1
2
3
4
5
6
Reading Brix pH TA Brix*pH^2 Ratio
1
2
3
4
5
6

Target Values

Brix pH TA(g/l) Brix*pH^2 Ratio (brix/TA) TA is in %
Low (<)
High (>)

Notes:

TA is expressed in g/l, (not %). To covert % to g/l, multiply by 10 (e.g. 0.75% = 7.5 g/l)

Brix*pH^2 is a concept put forward in Jeff Cox's excellent book, From "Vines to Wines" and is the brix reading times the pH squared. Jeff Cox indicates that this may me a "probably more accurate, measure of harvestability" (Vines to Wines, page 104). He recommends harvesting white wine grapes when this metric reaches 200 and red wine grapes when it reaches 260.

Ratio is also from Jeff Cox's (did I mention excellent) book that states that states: "Researchers at the University of California at Davis have found that wines are most in balance when the Brix:TA ratio is between 30:1 and 35:1. Here, he is referring to the ratio of brix and TA% (not g/l)

Disclaimer:

These are only guidelines put forward in various literature and an attempt by the web site author to provide an mechanism to easily gate your values.

I assume no responsibility for a premature or late harvest based on the results of these pages.

Tim Beauchamp