I pitched a packet of safale us-05 seven days ago into a wort with an O.G of 1.050. Today the S.G. is 1.020. Fermentor has been sitting in a room with an ambient temp of about 70 d F. I was going to wait a few days and recheck a gravity reading. In the meantime I was curious if it was okay to give the fermentor a shake in order to rouse the yeast back into suspension. Is this a no-no? Is oxygen still okay at this point in the process?