lacto starter; my first yeast infection?

Ingredients
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So last week I made a couple 1.5 liter starters for two packages of Wyeast 5335 destined for two 5 gallon carboys of Berliner wort.  Lacto were pitched to ~1.025 starter wort at 95F and held at steady temp for one week.  During that week one of the starters was producing a very small amount of gas bubbles.  I didn’t think much of it.  Prior to pitching the starters, they were sampled and pH tested. Tasted nice and sour with pH of 3.5. Into the fermenters they went to fresh un-aerated wort at 1.034 and 100F.  Just a couple hours later, the carboy that received the “bubbly” starter erupted into what I can only describe as a classic, vigorous yeast fermentation. Lot’s of gas, churning beer and lot’s of krausen that blew out the foam stopper and had to be replaced with  a blowoff hose.  I decided to just clean it up and let it ride for the planned week at 100*F.  The second carboy is nice and quiet and fairly clear compared to the other, as expected.

Anyone else experience this with a packaged lacto culture?  I’m assuming I received a packet contaminated with yeast of some kind. My sanitation is solid and likely a bit over the top.  I’ve never had to dump a batch at home due to contamination.

Any thoughts on the “infected” carboy.  I made my starter of 1007 for the clean batch last night. I decided not to make the second one for the “infected” carboy as I’m pretty confident that it’s fermented out into a hot fusely mess.  I’ll do some taste tests this weekend to see where its at but I’m not terrible confident.  Oh well, at least half of the batch should turn out well.  Appreciate any thoughts or comments folks may have with similar experiences.

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Interesting.  I have not had that happen before.  I am assuming your lacto starters were not on a stir plate?  The one that you noticed gas evolution in the starter wort, did you also notice any krausen forming when you swirled it?    Just trying to see what might have happened here…

Your best bet would be to taste the one you think is “infected” with yeast and see what pH it is.  It might be sour to your surprise.  Strange that both starters were sour and 3.5 pH yet you had a raging fermentation!  I have observed some lactobacillus fermentations that were fairly vigorous, but not enough to use a blow off setup.

I am hoping you will be pleasantly surprised and that you just made a fantastic environment for your lacto to ferment the Berliner!

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How did this turn out? How do they taste so far?

I wouldn’t assume you had an infected starter just yet - lactobacillus does produce CO2 and can be very active, especially at ~100F. Also, if you were growing yeast in one of your ~95F starters, the pH drop would have been less than the other. You would also have more sediment.

Maybe one pack of lacto was newer than the other, or stored less ideally? Maybe it saw more temperature fluctuation during shipping. I think the Wyeast/WL lacto cultures are quite fussy compared to yeast.

Please update the post with your results, good or bad. It’s definitely an interesting side-by side!