No chlorine is involved, nor is long term autolysis as the customer has detected soapy flavours in some beers within 10 days.
Soapy flavours are associated with fatty acids, capric acid in particular. The customer uses straight oxygen for his starters and on pitching. Normally the lipid content of yeast cells is about 2-5%, however de Clerk states "The lipid content of old yeast cultures, or yeast grown under conditions of strong aeration, may be as high as 10-20%." ( A Textbook of Brewing, Vol 1, p367).
I think this is the root cause of the problem, but am curious as to others' experiences, especially with straight oxygen.
Thanks for your replies Wolfy and Mark.
Pat