Duchess of Oldenburg is a popular early-season apple, primarily used as a cooking apple although it can be eaten fresh when fully ripe. It is often known simply as "Duchess".
The apples should be ripe in early / mid August.
The key to its success in the kitchen is its tart acidic flavor which holds up well in cooking. Slices usually lose their shape during cooking, making Duchess of Oldenburg best suited for recipes that require apple sauce.
Duchess of Oldenburg is a reliable variety, easy to grow, and produces apples from a young age. It is very winter-hardy and a great choice for the northern states. Disease-resistance is also excellent - except for fireblight, to which it is susceptible.
Advice on fruit tree pollination.
Duchess of Oldenburg originated in Russia in the early 18th century. It was introduced to the USA in the early 19th century, and quickly became popular in the northern states on account of its excellent winter hardiness. It was a mainstay of the University of Minnesota cold-hardy apple breeding program of the early 20th century, and features in the ancestry of many of the university's modern varieties - including Honeycrisp.