How many times can I re-use yeast?
 

Probably been asked hundereds of times, so apologies in advance.

I purchased a Wyeast 1728 Scottish Ale smack pack and it is currently fermenting its 7th batch. I do 14 litre batches each time.

To re-use, when I bottle straight from the primary after 3 weeks, I simply drain the yeast cake into a sterilised container and put it in the fridge. I generally use the yeast 1-2 days later.

Question - how many times can I do this? Each fermentation has been great and takes off very quick, sometimes in less than an hour. I have been hitting the FG's spot on each time with attenuation in the 80-85% range.

Guy in the local home brew shop said the yeasts can mutate. Will I get alien flavoured beer?

As long as it is turning out great keep going. I have read people using yeast into the 30th ish generation.. Preventing contamination is the key to long term success..