I had my girlfriend pick up my list of brew stuff the other day and when I checked the date on the Wyeast London Ale 1028 smack pack it was 9/20/2014. I just pitched this yesterday. I see that the wort burped a bit into the airlock but no other airlock activity since cleaning it out. Will an almost 4 month old pack of yeast still be viable, if it was kept refrigerated in the LHBS? How long should I wait to pop the lid and see if anything is happening before I pitch more?