2025 Post-Veraison in Pennsylvania - September 23

Report #4. Samples taken the week of September 15, 2025

This is the fourth weekly report for the third season of Post-Veraison in Pennsylvania (PVIP), a grape maturation reporting system across Pennsylvania vineyards. Reports consist of weekly grape ripening updates from cultivars that are planted widely across Pennsylvania (PA) vineyards (as based on feedback documented within Cultivars in the Commonwealth). Henceforth, PVIP reports will review the ripening patterns of some, or all, of the following cultivars: Cabernet franc, Chambourcin, Chardonnay, Riesling, and Vidal blanc. Due to the time required for grape samples to be shipped, processed, and measured, weekly reports will reflect maturation from the previous week. Participating stakeholders for the 2025 edition of PVIP manage vineyards in the following Pennsylvania counties: Chester, Erie, Fayette, Lehigh, and Snyder; thanks to these stakeholders for their participation and collaboration on this project. If you have a commercial vineyard in Pennsylvania, please let us know if you are interested in participating in a future edition of PVIP.

Note - these fruit samples are sent in from commercial vineyards; due to sampling methods and other factors, the samples may not necessarily represent the overall maturity of each cultivar across the entire block. These reports are meant to provide updates on general trends; some fluctuation from "anticipated ripening trends" in metabolites will be expected. For example, the persistently higher (and often increasing) titratable acidity values are expected to be due to the abnormally relatively dry and cool weather that has been experienced over the last several weeks. It is possible that the dry weather is concentrating the acidity (via smaller berries) while the cool weather is resulting in less acid respiration than would be experienced if overnight temperatures were warmer. Nonetheless, trends over time should give a good depiction of wine grape maturation across Pennsylvania.

Primary fruit composition: soluble solids (Brix), pH, and titratable acidity.

Samples from the week of September 15 revealed that Cabernet Franc was similarly and most advanced in maturity in Chester and Lehigh Counties. In Snyder County, Cabernet Franc had a similar composition except for a relatively higher titratable acidity (TA) (Figure 1). While Cabernet Franc in Fayette and Erie had similar Brix levels, the lower pH and greater TA in Erie showed that maturity was relatively behind at this location. Compared to the previous weeks' samples, Brix levels increased most dramatically in Chester County (+3.1) followed by Erie County (+2.1). While Brix increased similarly in Lehigh and Snyder Counties, a slight decrease in Brix was observed in Fayette County. Juice pH ranged from 3.18 to 3.22 in all counties except Erie, where juice pH remained lowest at 2.85. Relative to last week, pH increased by the greatest magnitude in Snyder (+0.18) and Lehigh (+0.13) Counties, while pH increased by a range of 0.03 to 0.09 in other counties. The lowest TA values were observed in Lehigh, Fayette, and Chester Counties, ranging from 5.55 to 6.00 g/L. In contrast, TA values were higher in Erie and Snyder Counties. Relative to last week's report, titratable acidity (TA) decreased by a large magnitude (-5.40 g/L) in Lehigh County; TA also decreased in Fayette and Chester Counties but increased in Erie and Snyder Counties (see note above about sampling errors and week-to-week fruit chemistry trends – regarding this result and other "atypical trends" throughout the report).

Note - the three counties that participated/are participating in PVIP in 2024 and 2025 are Erie, Fayette, and Snyder Counties. Average fruit composition from these counties is used to compare last year's and this year’s editions of PVIP. Relative to the fourth week's report from 2024 (samples collected during the week of September 16), last week's samples showed: lower average Brix (-2.0), lower average pH (-0.16), and higher average TA (+0.37 g/L). These differences suggest that, on average, Cabernet franc primary fruit composition in 2025 remains slightly delayed compared to the same period in 2024. In Snyder County, Brix and pH were relatively higher in last week’s samples compared to the fourth week of PVIP in 2024.

Chambourcin remained generally more mature in Chester, Fayette, and Snyder Counties compared to Erie County (Table 1). Relative to samples from last week, Brix increased at all locations, with the most pronounced increases (+2.4) observed in Fayette and Snyder Counties. Chambourcin pH also increased at all locations, but more so in Chester, Fayette, and Snyder Counties (+0.15 to +0.19 across those three counties) than in Erie County (+0.05). While Chambourcin TA increased in Erie County, it decreased in all other counties by a range of 4.05 g/L (in Snyder County) to 9.45 g/L (in Chester County). Chardonnay Brix and pH remained lower in Snyder County compared to Lehigh County, while TA was relatively lower in Lehigh County. Relative to last week's report, Brix and pH increased in both counties, while TA decreased in Lehigh County but increased in Snyder County. As indicated by the greater Brix and lower TA, Riesling maturity was more advanced in Fayette and Chester Counties relative to Erie County. Relative to last week’s report, the greatest changes in each metabolite occurred in Chester County, where progression towards maturity was observed as follows: an increase of 2.1 Brix; a pH increase of 0.19; a decrease in TA by 9.75 g/L. All metrics showed that Vidal blanc was more mature in Snyder than in Erie County. Relative to last week's samples, Brix and TA increased in both Erie County (+0.6 and +0.12, respectively) and Snyder County (+4.0 and +0.24, respectively). Vidal blanc TA increased in Erie County and modestly changed in Snyder County.

Primary amino nitrogen

Yeast assimilable nitrogen (YAN) is made up of two main components: primary amino nitrogen (PAN) and ammonium (NH₄⁺). Of these, PAN tends to be much more variable, while ammonium levels are usually more stable, averaging about 25–35 mg/L in grape must. YAN is a critical factor for healthy fermentations. If YAN is too low, fermentations can become sluggish or stuck, and the risk of producing hydrogen sulfide (H₂S) increases. As a general guideline, wines with <150 mg/L YAN are considered nitrogen-deficient and typically require nutrient additions before or during fermentation. However, the exact requirements can vary depending on the yeast strain and wine style. On the other end, excessive YAN (>250–300 mg/L) can also create problems. High nitrogen can promote the growth of spoilage organisms and has been associated with later issues such as reductive aromas.

PAN was measured in all cultivar samples across all counties during the weeks of September 1 and September 15 (data not shown). The average PAN across all cultivars during the week of September 1 was 131 mg/L, while the average during the week of September 15 decreased by 25 mg/L to 106 mg/L (data not shown). While averages across site and cultivar were unable to be determined due to incomplete replication (not all cultivars were measured at all sites), it appeared that Cabernet Franc PAN was relatively low (ranging 16-95 mg/L across both sampling dates) while Chambourcin PAN (ranging 76-268 mg/L across both sampling dates) and Vidal blanc PAN (ranging 127-233 mg/L across both sampling dates) tended be on the higher side (data not shown). Cabernet Franc PAN followed similar trends to the average across all cultivars, with values being much greater during the week of September 1 (88 mg/L) relative to the week of September 15 (47 mg/L) (Figure 2). At this stage, all fruit tested would be considered deficient in YAN. However, YAN levels are highly dynamic and can change substantially as fruit matures, influenced by factors such as vine nitrogen uptake, ripening progress, and weather conditions. For this reason, early-season measurements are not necessarily predictive of YAN levels at harvest. Further, we hypothesize that the decrease in PAN levels over time was potentially due to the continued dry weather patterns, which can result in dry soils and reduced nitrogen uptake.

Total sugars

It’s important to recognize that soluble solids (°Brix) only provide an estimate of ripeness, since they measure all dissolved compounds in the juice, not just sugars. Direct measurement of glucose and fructose gives a more accurate picture of fermentable sugar levels, which directly drive yeast activity during fermentation. Tracking total sugars, and the balance between glucose and fructose, provides a stronger tool for predicting fermentation performance and final wine style than relying on soluble solids alone.

Total sugar content (glucose and fructose) was measured in some cultivar samples across some counties during the weeks of August 25, September 1, and September 8 (data not shown). The total sugars across dates (averaged across only the cultivars measured during that time point – which wasn’t the same across dates) tended to increase over time; average total sugar values were 119 mg/mL during the week of August 25, 180 mg/mL during the week of September 1, and 204 mg/mL during the week of September 8 (data not shown). Cabernet Franc total sugars followed similar trends to the average across the cultivars measured across time points, with values increasing over time: 117 mg/mL during the week of August 25; 185 mg/mL during the week of September 1; 213 mg/mL during the week of September 8 (Figure 3).

Pennsylvania stakeholders have already reported harvest for some cultivars in the 2025 vintage, including Albariño, Aromella, Cayuga White, Chancellor, Chardonel, Chardonnay, Gruner Veltliner, Marquette, Pinot grigio, Pinot noir, Riesling, Sauvignon blanc, and Seyval blanc. If you have harvest updates you wish to be included in this report, please email them to viticulture@psu.edu.

The data in this report is possible due to the funding and support of the Pennsylvania Wine Marketing and Research Program. The authors and collaborators are grateful for the support.