Meair Right now I will suggest go ahead and cash in those berries for energy. The double production week is a long way to go now and you will need only enough berries to make cakes for 7 days.
There will be more chances to save, also a double materials week in between, when you can use green rings in chamber of fortune to get quite some berries for the cakes.
Moreover you might even reach Scandinavia by then when the berries will become useless and everything changes.
So for now, go ahead and spend those, enjoy few hundred energy to play the game! 🙂