Hello, I bought a Hefeweizen kit 2 weeks ago and did open today. I did know I was supposed to refrigerate the liquid yeast. It has been in cold dark garage however. Can I still use it or do I need to order more?
Should be fine unless the yeast underwent several rounds of freezing. If the temps stayed above freezing in a cool space, it's probaby not much different from storing the packet in the fridge.
If you have any suspicion temperatures reached freezing over that time period I would try making a starter and see if there is viable fermentation. If you don't have the ability to make a starter or a few days to see if the starter takes off, might as well buy fresh yeast.
Hefeweizen yeast are hardy yeast so outside of freezing I wouldn't be too concerned.
I did pretty much the same thing... left in basement in the mid-60s for a couple of weeks. Mine was fine. Mashpaddled's suggestion on making a starter is a good one.
If it's close to the "expiration date," or when in doubt about her health, make a yeast starter, if you can.
Aside from growing more cells, and rejuvenating the existing ones, it proves viability.