Re using a yeast cake
 

I've had a batch in the fridge for the last couple of weeks to clear and am planing on bottling it tomorrow.... can I reuse the lees? would the cold have caused the yeast to die out or will it just take some time to restart?

Obviously I will have to use new juice e.c.t.

the yeast should wake up after coming back to room temp. yeast can be reused over and over. Guinness claims to use the original yeast they started with!

I have done this and it definitely works, fermentation started back up within a day after getting out of the fridge and having fresh juice on it.

What is the process to using this?

If I wanted to do a back to back cider, do I need to clean the lees out of the last batch or can I just re-add the fresh juice to the carboy?

If you just racked off the lees, then you can add the new juice immediately.

If you keep reusing the yeast, does autolysis eventually become a problem?

Yes, as does yeast mutation. There is a sticky somewhere in the beer forum (fermentation & yeast I think) about yeast washing which is a safe way to separate the viable yeast from the dead cells.

Well after racking I thought why not give it a go.... as I had 2 batches I had racked I combined the lees (bothe the same yeast from the same batch) added more juice (all my leftovers e.c.t) some more sugar a good old dollop of nutrants and air locked it.... twas away within an hour the fastest ferment I've ever had.... few days later ferment has slowed I will give it a couple more weeks and then see what my yeasty beasty is like.