Harvested Yeast from Commercial Bottles (Bells Winter White), concerned about contamination.

[sixwinds]

One of my homebrewing goals this year is to get more involved in yeast handling. I've started harvesting yeast from my batches and saving them in the fridge for future use.

Last weekend I decided to attempt to harvest some yeast out of some commercial bottles. I went for a six pack of Bells Winter White ale which is unpasteurized and apparently uses a hybrid yeast (cross between 3711 and hefe).

To harvest I poured almost all of the beer out of three bottles, then the dregs were swirled and poured into a sanitized and sealed mason jar. I let the jar warm to room temp over a few hours and then made a starter.

I messed up the volume on the starter and created a 500ml starter using 100 grams of DME, instead of the 1L starter I was planning for, oh well.

I pitched the dregs into the starter, covered it with foil, and let it sit on the counter. Absolutely nothing happened for about 3 and a half days. I was ready to toss it and call the experiment ruined, but then I noticed some activity.

This morning the starter was bubbling happily and appears to look like any other yeast starter I've made.

My concern is with possible contamination due to the starter wort sitting out on the counter for almost a week with just foil covering it. Since the yeast too so long to get going could there be anything else growing in there with them? If so could that something else be dangerous and how can I make sure nothing bad is going to show up if I use this starter in a 5 gallon batch?

Thanks!

 

[LLBeanJ]

Anytime you're working with fermentables contamination is possible. Whether your starter is contaminated or not is hard to say. My approach is to assume it's fine until something suggests to me it's not (smell, taste, or visual). One thing that would concern me is the density of your starter wort, which, according to my math, is in the neighborhood of 1.080. When bottle harvesting, you're starting with a small amount of likely low viability yeast, so to grow those cells into a larger colony, the first step is normally with a small volume of low (1.020-ish) gravity wort, so that the cells are not stressed as they're brought back to life. Now, with that said, all of my starters, including bottle harvested ones are done with 1.040 wort and I've never had an issue. Starting them off with 1.080 wort, however, would definitely cause the little buggers a bit of stress, I would think, so if you have any concerns at all, that's where they should lie. Nevertheless, once your starter is finished, I'd give it a smell, and if it smells okay, cold crash it and decant the starter "beer" and give that a taste. If it tastes like vinegar or is noticeably sour, it's probably contaminated. If it doesn't have any weird or offensive flavors, I'd brew something with it and see how it comes out.

 

[cegan09]

There's a ton of variables. How long the yeast has been sitting in that bottle, size of the starter, how the beer was handled before you got it, etc. Some of my bottle harvests have taken off fast, some lagged a few days.

I'll agree with the above though, if it was much above 1.05 you likely stressed them out a lot. May be worth redoing with a lower first step.

as far as infection, does it smell bad? Taste bad? if not, probably fine. It's not going to smell amazing since it's not temp controlled and it was likely a stressful environment, but normal yeast smell and infection smell differently.

 

[sixwinds]

Awesome, thanks for the advice! I think I'll let the current one ride and see how it turns out, and try again with another batch and lower gravity starter.