How much Fresh Yeast to use?

[Dephlegmator]

I have been using fresh yeast from my local supermarket bakery, it comes in a brick but crumbles up very easily.
when I use it for a 20-25L wash, I simply put it into a stainless bowl and add about 50ml of wash to it, mix it up till it is a consistent slurry.
Sometimes I will cover the bowl with glad-wrap and leave for half an hour but find this is usually not necessary as the yeast does not need to rehydrate.
I started off using 300g of yeast per batch
Now have been using 200g
I still believe that this could be quite excessive and I could save a little money by using less per batch.
Does anyone have any recommendations with how much to use? or should I just keep trying less till I notice a change in my brew.