You can pick them before the frost and infuse the fresh berries in water over night and then change the water before cooking them into a jam or jelly. This will remove much of the bitter taste (but also some of the vitamins).
These berries are also good as a chutney (goes well with venison
) in which case you throw away the water after boiling them.
In Bavarian they are called Vogelbeeren = bird berries
Around here the jelly is also used with venison (and game).
Oh, and: Frost also reduces the vitamin-content.