I have made a 1 l yeast starter for my wheat beer I plan to brew. I am using Wyeast activator 1010 American Wheat. I boiled my light DME and water, cooled it down to room temp. I had expansion of the yeast smack pack. I dumped it into the flask and put my airlock on. 24 hours later I see no bubbling in the lock and it seems that the yeast have all settled out of the solution and have collected on the bottom of the flask. If I stir it, I get vigorous bubbling for a few seconds. How can I tell if my starter is viable or not?