Enzyme Precipitation - Ammonium Sulfate or Acetone?

I am working in the production of cellulase from fungus (molds) like Aspergillus niger, but I have problems with the precipitation with ammonium sulfate. I don't see any precipitation in the different fractions, neither after centrifugation at 14,000 rpm for 10 min. To produce the enzymes, I use solid state fermentation and for the extraction sodium phosphate buffer 50mM ph=6. I don't see precipitation yet, even at 70% concentration of ammonium sulfate.

I tried precipitation with acetone with good results, but in some cases the protein loses the activity or became insoluble.

I tried different protocols to precipitation with ammonium sulfate but I don't see good results. The concentration of protein in my crude extracts are about 0.05 mg/ml to 0.5 mg/ml (bradford method).