Since it takes me a week to express and purify protein everytime when I need protein for crystallogenesis experiment, I am wondering if we could store the purified protein at -80C at use it later for crystallography ?

If so, what are the good conditions of storage (detergent, flash freeze, slow or flash unfreeze ?)

For information, my protein is a lipase and its pI is 6,28. I tried to flash freeze in liquid nitrogen my protein at 1mg/ml which in a solution of 50 mM Phosphate Buffer Salin (Na2HPO4), 0.2 M NaCl, 2mM DTT, pH 8; then I stored them in -80C. 2 days later, I unfreezed  them at room temperature, I didn't get any precipitation; but after 10 days, I saw small precipitation in my protein stock after unfreeze at room temperature.

Thank you