Will added yeast overpower wild yeast?

I'm making a basic Pilsner for the summer. Since I finally got myself a house, and it came with an extra fridge, I decided to try a cold fermenting lager. I prepared the wort and added tap water to top it off at 5 gallons. I then set it aside at 70 degrees for a few days while I prepared the fridge and got the temperature right.

2 Days later, I go to add my yeast, and find it already fermenting. There was a mild froth, and fairly active airlock. I'm assuming a wild yeast in the tap water?

I added the yeast anyway, WLP800. I didn't bother with a starter, as it'd just give the wild yeast an even further head start while it prepared. So I'm assuming there's a yeast war in my bottle. Any chance the WLP800 will overpower and kill the wild yeast?

That's one hell of an impressive wild yeast if it can build its numbers up fast enough to show activity in a few days. Sure you didn't just have some protein bubbles and air lock activity from temperature changes?

If you have something wild in their, it has a foothold and will continue to grow. The 800 might get the upper hand, but it won't kill the wild.

A good point. Regular yeast seems to take 24 hours before visibly fermenting, and that's with millions introduced in visible amounts. A few microscopic yeasts shouldn't be able to reach a population that shows activity for much longer. The temperature change is self explanatory, but can you explain the protein bubbles?

If you don't hear from me again, come looking for me. This yeast is wild!

The one thing in your favor might be temperature. Depending on what it is you've got in there, the lager yeast (bred for cool fermentation) might eventually out-compete it (it would never actually kill the other yeast, just multiply faster).

Whatever happens, it should be interesting.

"A few days at 70 degrees" before pitching the yeast is plenty long enough for wild yeast or bacteria to take hold and ruin the batch.

Yooper said:

"A few days at 70 degrees" before pitching the yeast is plenty long enough for wild yeast or bacteria to take hold and ruin the batch.

Click to expand...

I agree. I had this happen to some batches lately and generally the wild yeast will produce some terrible flavors that the other yeast will not be able to get rid of. What I experienced were bandaid smell and horrid plastic taste. One batch I even dry hopped quite a bit since it was an IIPA, but I could still taste the off flavors in the background and it just got worse as the hops aged out. These flavors don't seem to really age out either. In a clean pilsner there would really be nowhere to hide the off flavors.

Yooper said:

"A few days at 70 degrees" before pitching the yeast is plenty long enough for wild yeast or bacteria to take hold and ruin the batch.

Click to expand...

^this^

I doubt your pitch would 'overpower' whatever has started fermenting your wort, seeing as it's already taken hold.

Paniller said:

A good point. Regular yeast seems to take 24 hours before visibly fermenting, and that's with millions introduced in visible amounts. A few microscopic yeasts shouldn't be able to reach a population that shows activity for much longer. The temperature change is self explanatory, but can you explain the protein bubbles?

Click to expand...

Probably not the correct term, but just normal bubbles that the proteins and what not of the beer allow to form. Just because they are there does not mean that they are their from yeast activity. Not saying that its not a possibilty, but a few wild yeast cells growing enough to cause a krausen to form in a few days would surprise me. If it is wild yeast, you will likely have a ruined beer, unless you get lucky and they make pleasent flavors and you will have a nice wild brew on your hands sometime next year.