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 4
Welcome to week 4 of the Midwest Wine Grape Berry Composition Report!
was able to visit several vineyards during harvest since our last report. Some of those locations were machine-harvested, and others were harvested by hand. One of the items that always impresses me with properly adjusted machine harvesters is the number of green/unripe berries that remain on the clusters and do not end up being harvested (see photo on the right).
One common topic brought up in some of these visits was that, in general, the reds have a lot of within-cluster variation. Some of this could be crop load-related, weather-related, or cultivar-related. Petite Pearl, Marechal Foch, and Frontenac seem to have some within-cluster variation so far. Our high temperatures could have limited anthocyanin production in some situations. Previous work (Spayd et al. 2002) indicated that Merlot berries in the sun can be more than 20 degrees warmer than the air temperature. That same work showed that anthocyanin production was inhibited by the number of hours the berry temperature exceeded 95F. So, it’s possible some berry pigmentation could have been impacted, given our air temperatures recently (and forecast for next week) have been quite warm.
Berry Report Comments/Highlights
Brianna:
- Most of the sites have been harvested.
Edelweiss:
- Half of the sites have been harvested.
- TA has been dropping 4-5 g/L each week over the last couple of weeks.
Plocher red cultivars (Crimson Pearl, Petite Pearl, Verona)
- The TA on nearly all of these is 10 g/L or less. This is something that growers appreciate about these cultivars and why they have had increasing interest.
Frontenacs
- The TA has dropped to ~15g/L or less at all sites.
- There have been visual reports of shriveling, and the berry weights have been stable to slightly decreasing.
La Crescent
- The TA has dropped to ~15g/L or less at all sites.
- Several sites have been harvested.
Marechal Foch
- The pH at all sites is higher than 3.
Marquette
- The TA at all sites is 14 g/L or less.
- Some growers have harvested Marquette, and others are considering harvesting soon.
Please don’t hesitate to contact us with suggestions with how to improve our report!
References:
Spayd, SE, JM Tarara, DL Mee, and JC Ferguson. 2002. Separation of Sunlight and Temperature Effects on the Composition of Vitis vinifera cv. Merlot Berries. Am. J. Enol. Vitic. 53:3
Commercial Fruit Crops Field Specialist
Iowa State University Extension & Outreach