Danube sweet-tart cherries
These are often listed as tart cherries, but are actually a cross between tart and sweet cherries and exhibit characteristics of both. The Erdi cultivars originated from a breeding program in Hungary. Amy Lezzoni, a cherry breeder and researcher at Michigan State University, brought them to the U.S. several years ago.
Shared characteristics observed at Carandale Farm
The ripening period is intermediate between sweet (P. avium) and tart (P. cerasus) cherries, as is the brix level (sweetness). These firm cherries pick with a dry stem scar and can be stored and eaten out of hand like a sweet cherry. But they have enough tartness for processing into pies, wine, jam, cordials, etc.
Fruit bud hardiness, chilling requirements and pest resistance also seem to be between sweet and tart cherries. Both Erdi cultivars are vigorous, semi-dwarf trees that produce at least some fruit annually (unlike the sweet cherry cultivars), but they have never produced what could be called an abundant crop at Carandale Farm. Both were purchased from Northwoods Nursery (see One Green World) and are grafted onto Colt rootstock. Both cultivars are considered cold hardy to at least -25 degrees F, and are said to be self-fertile.
Tart cherry juice has been found to reduce inflammation and related pain in a study of long-distance runners (Kuehl et al., 2010).
Cultivar-specific observations at Carandale Farm
Danube sweet-tart cherry tree in bloom
‘Danube’ (Erdi Botermo cv) has a spreading tree form reminiscent of its tart cherry heritage, but an earlier bloom time characteristic of the sweet cherry. Fruit color is bright, red similar to most tart cherries, with pigmentation throughout the flesh, making it a ‘Morello’-type (though lighter colored than most). On the other hand, it is the sweeter of the two with up to 23 brix. Although it blooms earlier than its sister cultivar (‘Jubileum’), it ripens about the same time or somewhat later. Fruit quality and good shelf life make this a good selection for retail and direct market. ‘Danube’ has a high anthocyanin content (Kim et al., 2005). This is a good cultivar in nearly every respect except for yield, and perhaps that could be improved with a different rootstock selection.
Jubileum sweet-tart cherry tree in bud
‘Jubileum’ (Erdi jubileum cv) has a more upright tree form similar to most sweet cherry cultivars, but it blooms later than ‘Danube’ despite the fact that it ripens earlier. The accompanying photographs taken on the same day show ‘Danube’ in full bloom when ‘Jubileum’ is just coming into bloom. Ripening time can be deceiving. ‘Jubileum’ is such a black-red fruit that it can appear ripe even when it should be left on the tree for a week or so longer for optimum sweetness. The fruit is large and remains firm for a long time. Fruit and juice are dark red. It has a high anthocyanin content (Kallay, et al). Fruit quality is excellent, but yields have been disappointing. It has been less fruitful than ‘Danube’.
‘Balaton’ is also from Hungary, introduced to the U.S. by Amy Lezzoni at Michigan State University. It is not the result of an intentional breeding program but rather a superior selection identified from a large amount of plant material collected throughout Hungary. It was first released as a commercial variety in Hungary in 1970. After years of testing at MSU under the name ‘Balaton’, it was introduced in the U.S. Half of the tree royalty (25 cents) is returned to Hungary.
‘Balaton’ is considered to be a true tart cherry (Prunus cerasus) of the ‘Morello’-type, though it is somewhat sweeter than the typical tart cherry and behaves more like some sweet cherry varieties in regard to winter injury. This cultivar has been gaining in popularity because of its red juice and associated nutraceutical benefits, but its lack of winter hardiness may limit adaptability. It was added to the test plot in 2010, so observations are limited. It does appear to be quite precocious because it had some bloom (though no fruit set) in 2012. Plants were purchased from St. Lawrence Nurseries.
One Green World
Kuehl, KS, ET Perrier, DL Elliot and JC Chesnutt. 2010. “Efficacy of tart cherry juice in reducing muscle pain during running: a randomized controlled trial.” Journal of the International Society of Sports Nutrition 2010 7:17. <http://www.biomedcentral.com/content/pdf/1550-2783-7-17.pdf>, accessed 6/27/13.
Kim, D, HJ Heo, YJ Kim, HS Yang, and CY Lee. 2005. “Sweet and Sour Cherry Phenolics and Their Protective Effects on Neuronal Cells. J. Agric. Food Chem 53 (26): 9921-9927. <http://pubs.acs.org/doi/pdf/10.1021/jf0518599>, accessed 6/27/13.
Kallay, E, M Steger-Mate, M Mester-Ficzek, G Sandor, G Bujdoso, and M Toth. 2008. “Changes of polyphenol, anthocyanin and rutin content in sour cherry varieties during ripening.” Acta Biologica Szegediensis 52(1): 217-219. <http://www2.sci.u-szeged.hu/ABS/2008/Acta%20HP/52217.pdf>, accessed 6/27/13.
Michigan State University Department of Horticulture information on Sweet-Tart Cherry