I brewed a belgian triple last week. I was making a starter using white labs trapist yeast, but it didn't take off; must have been a bad vial. So, I picked up a packet of wyeast trapist yeast and pitched that into the same starter to get it going. In the meantime the batch was sitting in the carboy waiting for yeast.

Problem is: while the starter was getting going, and before I pitched any yeast into the carboy, the cooled wort in the fermentor started to ferment. It didn't get going too hard before I pitched a good size starter into it.

Question is: What is going to be the effect of whatever got in to the batch to start it fermenting? And, since I pitched a really healthy starter that made fermentation take off, will the yeast I pitched take over and still make a good tripel?

EDIT: for clarification: When my first starter didn't take off, I added more yeast to it (wyeast). In the meantime, while waiting for the wyeast starter to get going the carboy of wort started to ferment on its own.

  • How many days was it between the two yeast pitches?
    – nbushnell
    May 10, 2011 at 21:46
  • Timeline: sun pitched white labs into starter. monday brewed the batch. tues pitched the wyeast into the starter. wednesday morning the carboy was foaming slightly and the airlock had a little bubbling so i pitched that starter on wed night
    – Bullet86
    May 10, 2011 at 22:10
  • UPDATE: Just transferred to secondary. I know it isn't necessary but with how cloudy the beer still is I have decided to let it sit another couple of weeks and wanted it off of the giant wild yeast cake. The beer smells, well, like beer and the FG came out at 1.13 as opposed to the expected 1.16
    – Bullet86
    May 17, 2011 at 17:23

3 Answers 3


There's a strong likelihood that the "wild yeast" that started fermenting your wort is residual yeast in the carboy (or other equipment) from your last batch. Something wasn't properly cleaned and sanitized, and the microorganism in highest abundance is generally your last yeast, so that's what has the best odds of survival.

If this is the case, though, the yeast may or may not bear strong resemblance to the last yeast. Because the colony has repopulated from a relatively small sample, with unknown origins and health, I would expect the aroma and flavor to resemble the parent yeast, but with possible profile differences due to the means that the yeast were "selected" and the limited base for the genome.

You could make observations about the character of the fermentation, krausen, trub, aroma, and flocculation (and later, the flavor) - these would not only hint as to whether these yeast are the children of those you recently used, but might suggest where the contamination came from - for instance, if this yeast is exactly like your last yeast except more flocculent, then it would be possible that the colony started from yeast cells on the bottom of your carboy which were the first to flocculate in the last batch.

  • Nice point about the last yeast being the the microbe with highest abundance.
    – brewchez
    May 12, 2011 at 1:19
  • I see what you are saying. Here is my thought on it. I feel I have very good cleaning techniques. That being said, if there were residual yeast it would have had to be such a small amount that I wouldn't have seen it, and would that small of an amount started fermentation after three days?
    – Bullet86
    May 12, 2011 at 4:22
  • If your cleaning is so thorough, then why did your wort ferment before you pitched yeast? ;) And obviously whatever got in there was in trace quantities regardless of its origin.
    – Brandon
    May 13, 2011 at 1:03
  • Touche. I had figured on something getting in between cooling and racking into the carboy. Good call on anything that got in being in minute quantities.
    – Bullet86
    May 13, 2011 at 16:33

Unless something bad happened I think the slight foaming you saw on Wednesday was the original yeast and not wild yeast. Perhaps the wort was too hot or too cool when you pitched the first time and it took a while to kick in or as you said a bad/old vial. The wyeast trapist yeast (what little bit grew) and the white labs trapist yeast will both be active for the fermentation. The beer will be just fine.

  • 1
    Let me correct you. I had the white labs and the wyeast in a flask on a stir plate. I never pitched yeast into the wort. The wort started fermenting without me pitching anything into it.
    – Bullet86
    May 10, 2011 at 23:18

Well your beer will definitely be a "wild brew" so there's nothing else to do but sit and around and see what happens. And I do mean "sit" because you'll probably need to wait 5-6 months to make sure the wild yeasts have done their thing to completion before you bottle.

I'm glad you pitched the Wyeast instead of chucking the whole thing. All you can do now is give it time. You might want to do a little research on how safe the final product is. Since its not primarily fermented with Saccharomyces Cerevisiae, there could theoretically be a danger in drinking it, although probably not. If the beer smells like "beer", then you are all good and it wasn't wild yeasts! Drink up!

The Mad Fermentationist recently experimented with wild yeasts as primary yeasts and he's prob got some good info, so google him and read his blog.

I'll say that probably the beer will be pretty nasty in the end, but you never know. Could be wonderful. Scratch this, sounds like it will all be fine.

  • Can you elaborate further on on the danger in drinking it?
    – roto
    May 11, 2011 at 15:59
  • I can't, and that's the danger. Sugary wort fermented with normal beers yeast is always safe to drink, but since any number of fungi, molds, and bacteria got in there, we don't know what organisms are present in the final product. I'm just pointing out that this beverage is outside of the normal "beer" range, and therefor we can't just assume its safe to drink. If it smells like alcohol or vinegar or some combo of the two, then its probably safe, but if it smells like puke or rotting meat, then its a different story.
    – GHP
    May 11, 2011 at 20:43
  • As of now (one week in carboy) it has mostly fermented out. I have yet to take a reading but the krausen is gone, no film on top, and I notice no horrible odors coming out of it (I actually think is smells better than a wheat extract beer, those always smell funny to me when young)
    – Bullet86
    May 11, 2011 at 22:37
  • I was under the impression that all beer was safe to drink, just not always enjoyable. May 16, 2011 at 20:03
  • Nathan, "beer" is a grain based beverage fermented with yeast. If you leave a bucket of wort out in the open to ferment wild, it will collect non-yeast organisms as well as normal (albeit wild) yeast. The molds and fungi that can set up shop in a wild fermented beer are not necessarily safe. As an experiment, drain off the last pint from your next batch and leave it exposed in a jar outside. What you will find there, after a day or two, is most certainly NOT "beer."
    – GHP
    May 17, 2011 at 12:30

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