By Dr. Aude Watrelot –
Petite Pearl is a cross between MN 1094 and E.S. 4-7-26 with Vitis species such as V. vinifera, V. riparia and V. labrusca among others. Tom Plocher in Hugo, Minnesota bred Petite Pearl in 1996 and the release of it wasn’t until 2010. Petite Pearl can resist to temperatures as low as -32°F. This cold-hardy grape variety is highly resistant to powdery and downy mildew, to black and bunch rot. Based on a report from the Northern grape project (Gomez et al., 2016), Petite Pearl does not seem to be susceptible or injured by copper-fungicide and sulfur-fungicide when applied in Wisconsin.
Bud break is late spring and it is a late-ripening variety with a range of GDD between 1350 to 1500 C (Plocher & Vines). The grape berries of Petite Pearl are black, weighing 2 g, compact and the clusters are very dense.
In a recent study, Scharfetter et al. (2019) measured the effect of leaf removal on polyphenols of cold-hardy grape varieties including Petite Pearl. The vines were planted in 2011 and were trained to a high cordon system. The harvest times varied from October 2nd in 2015 to September 12th in 2016. The yield was between 11.7 to 6.2 kg/vine at the respective harvest dates and the Ravaz index was 13.7 and 5.0 kg fruit/kg pruning, respectively.
The harvest parameters were between 18.4 to 20.8 °Brix, with a titratable acidity (TA) between 8.9 to 11.0 g/L tartaric acid equivalent and a pH between 3.30 and 3.45 in 2015 and 2017, respectively.
In 2017 one-week postfermentation wine, the °Brix was 7.3, the TA was 7.77 g/L tartaric acid equivalent and the pH was at 3.62. The total phenolic concentration measured by a modified Folin-Ciocalteu method, was 1439 mg/L gallic equivalent in the control and significantly higher in wine made from leaf-removal treatment grapes. The concentration of monomeric anthocyanins and polymeric pigments were significantly higher in wine made from leaf-removal treatment grapes.
Petite Pearl has a lower acidity and seems to be rich in tannins compared with other cold-hardy grape varieties, however no research has been carried out on tannin content and structure of this new cold-hardy grape, yet.
For in-depth information:
Gomez, M., Kananizadeh, S., & Oh, D. (2016). Cost of Production in Cold Hardy Grapes. 11.
Plocher, T., & Vines, P. (n.d.). Petite Pearl Culture and Winetasting. 15. https://cdn.ymaws.com/www.mngrapes.org/resource/resmgr/CCC_17_presentations/Eno_Sat_4_Petite_Pearl_Tasti.pdf
Scharfetter, J., Workmaster, B. A., & Atucha, A. (2019). Preveraison Leaf Removal Changes Fruit Zone Microclimate and Phenolics in Cold Climate Interspecific Hybrid Grapes Grown under Cool Climate Conditions. American Journal of Enology and Viticulture, 70(3), 297–307. https://doi.org/10.5344/ajev.2019.18052