I saved some dregs from a lager I brewed last fall in a sanitized growler. Been in the fridge for at least 9 mos. I made a starter last night and pitched the sediment. Today there’s a nice krausen on top and it smells like yeast- not cidery or anything else concerning. I was kinda surprised how quickly this got going and that makes me concerned about its purity. Is there a reliable way to be reasonably sure I’m ok with this yeast before I pitch it into 10 gallons of helles next weekend? I’m not brewing for another 10 days so I’ve got plenty of time to build a nice big starter. Thanks.