Is my starter ready?

Hey everyone,

I washed some wyeast 1084 about 4 weeks ago and stored the yeast in the fridge up until yesterday. I decided that it would be a good idea to make a starter to check if the yeasties are still viable. I used 2 cups of water to 1/4 cup Light DME. I cooled the mini wort and pitched ontop of the washed yeast in the growler. I shook it really well for a couple of minutes and topped the growler with some sanitized plastic wrap. A couple of hours after I aerated, A mini krausen formed. It wasn't that big so I don't know if it was just from me shaking the starter or if it was the yeast top fermenting. It's been about 18 hrs and I still don't see and vigorous bubbling. Is this because the yeast are still replicating and haven't started fermenting the sugars yet? I plan on brewing within the next few hours. What would you do? Posted is a pic.

I personally would have let it go longer, but I'm sure that it is fine to use as long as the original yeast wasn't incredibly old.

thanks. The yeast is about a month old from brew date. I didn't record the manufacturing date, so who knows...

If the starter is showing signs of a krausen then its probably not done. Usually the starter will begin to "bubble", a krausen will form, and the wort will change from a darker brown to a lighter brown color. Then the krausen will fall back into the beer. Afterwards the yeast will settle into a nice little "cake" at the bottom your starter.