Starter With Lager Yeast

[BenTheBrewer]

I brewed a cream ale using Wyeast 2112 Cal Lager yeast. I made a 2000ml starter by using half a cup of DME and some nutrient. I boiled it for 15 mins then cooled and pitched the yeast. I let the starter sit for 4 days covered in foil. I smelled it on brew day and it didn't smell right. Almost sour. I pitched it anyway along with another smack pack of 2112. I'm fermenting at 67°-68° F. The air lock smells a little sour. I hope it's just the lager yeast, but it could be infection. I know that the only way I will know for sure is to let it ferment out and taste it, but I don't want to ferment for 2 weeks and lager for 4 weeks to find out that it is sour. Any thoughts?

[Quin]

You should be able to taste the sourness after fermentation stops. Check your gravity and then taste the sample. You'll know if it's sour or just the sulfur from the lager yeast.