© Max Straeten, Belgium
Bumbleberries are not a type of berry; in fact, they don’t really exist.
It’s a made-up word to describe a random mix of berries used in a dish, such as a pie. It’s usually a mixture of berries that are in season (ones that you might “bumble” upon), and so happen to be the berries most in need of using up at that point in time.
You can even use frozen berries to create a Bumbleberry mixture.
For a bumbleberry pie, you need roughly 750 g / 25 oz (5 cups in volume) of fruit — it doesn’t even have to be all berries. Bumbleberry pies, in fact, usually include other fruit as well, such as rhubarb and / or apple.