I made a mistake while stepping up a starter. After boiling it for 10 minutes, I threw the starter wort in the freezer UNCOVERED to chill it down to pitching temp. A little while later, I realized I had forgotten it in there. When I got back to it, the wort had started to freeze. I then threw it back on the stove to bring it back up to pitching temp and poured it into the flask. I did not boil it. What are the chances I just introduced something nasty into my starter? Should I pick up a new pack of yeast and start over or am i good to go? I'd rather not waste an entire grain bill.