Midwest Grape Maturity Analysis 2023 (week 6)

The MGWII has teamed up with Randall Vos (ISU Extension) to perform grape maturity analysis for multiple locations across Iowa and one site in Illinois.

Each week during the harvest season you’ll receive this email with a link to the data for multiple cultivars and the current week’s analysis of soluble solids (Brix), pH, TA and berry weights.

Please consider sampling your own vineyard as well to get an accurate picture of grape ripening. Please contact Randall (rjvos@iastate.edu) or the MGWII (wine@iastate.edu) if you have any questions, or need help to get a sampling program started.

2023 Midwest Wine Grape Berry Composition Report: Week 6

https://iowadot.gov/maps/Digital-maps/City-and-county-maps

Based on the feedback from our sampling locations, we will have two more weeks of the report. This week’s report reflects the last four weeks of sampling (Weeks 3-6)

At some locations, we see downward trends in berry weight in the Frontenacs and Marquette. The challenge is that it gives a skewed view of the berry maturity when looking only at brix values. When there is considerable berry dehydration, brix values will continue to increase. Still, some of this is due to the concentration of the sugars in the berries rather than an increase in sugar being translocated into the berries. In the figure below, I charted the brix from the last four weeks from two locations that had not harvested Frontenac before this report (Marion County=M; Webster County=W).

In the graph, the solid lines are the actual brix values from the report, and the dotted lines present a calculation of what the brix (adjusted brix) would be if the berry weight had not changed from Week 3. For example, the brix increased each week in the Marion County samples, but the adjusted brix was relatively unchanged from weeks 4 to 6. This means that the gains in brix were primarily due to the decrease in berry weight from 1.05 grams in Week 4 (8/28) to 0.96 grams in Week 6 (9/12), not due to more sugar moving into the berries.

In the Webster County samples, there were increases in brix and adjusted brix from Week 4 to 6. The brix increase was more significant than the adjusted brix. This indicates the rise in brix was due to both an increase in sugar translocated into the berries and dehydration.

I ran the numbers on several cultivars that I’ll get into more detail in my Viticulture Newsletter sent out on Sept 15.