How many times can you reuse a cake?

[Lando]

I have a cake of Safale05 that is on its second batch right now. I am guessing that the trub gets thicker and thicker every time you reuse it.
Any idea how many times you can reuse a cake before it's no good?

 

[Orfy]

rot 3..........

 

[ChshreCat]

I've heard it peaks at about the third generation and starts to go downhill about the 5th. Don't know from experience though.