No activity in starter

I made a 2L starter last night, using White Labs Cal Ale V yeast, for brewing today. I added 1/2 teaspoon yeast nutrient and oxygen for 10-15 seconds. This morning, there is no krausen and no indication that CO2 is being produced (my foil "lid" is not bulging, and no tell-tale hissing when I swirl it). The yeast started foaming when I opened the vial, so I'm pretty sure they were alive and well at that point. All of my past starters have been active and showed krausen by this point. Should I be concerned about this?

It is possible that you put so much O2 (sounds like you injected it) and sugar in the solution that the yeast have not had to make CO2 yet. Did you pitch the yeast into just boiled wort? If you can't think of anything you did wrong, then give it another 12-24 hours. Can you put an airlock on? That way you won't have to keep opening it.

pkeeler said:

It is possible that you put so much O2 (sounds like you injected it) and sugar in the solution that the yeast have not had to make CO2 yet. Did you pitch the yeast into just boiled wort? If you can't think of anything you did wrong, then give it another 12-24 hours. Can you put an airlock on? That way you won't have to keep opening it.

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I think you nailed it. I pitched into 75F wort and used an O2 stone and injected it (my first time using it with a starter).After I got back from taking my kids to school this morning, there was the slightest beginning of krausen. I swirled it and there was clearly CO2 pressure in the headspace. Thanks for your prompt and informative response.