Can bad yeast affect/damage good yeast? WLP002

[Alex4mula]

Hi. I brewed this pumpkin latte 10 days ago with all grain recipe. OG was supposed to be 1.062 but with my process not being too efficient yet I got 1.49. FG was supposed to be 1.016. When I got the pack of WLP002 it didn't look as good as others I have used from them. Looked kind of dark and expiration was next Sept 30. So not wanting to risk anything I got a new fresh pack of WP002 with expiration of Jan 3 2020 that looked right. At the end I pitched the new one and just in case half of the other one. Beer fermentation started in about 12-15hrs and seemed to ferment quickly with Krausen rising and dropping in about 3 days. Today I took a gravity measurement and it was 1.20. Usually my beers FG get to expected FG and most common 1-3 points lower. I think probably all is ok but not sure. Since many pitch new yeast when one doesn't work I don't think the high FG is because of the not looking good yeast that I added. What do you think? It fermented at 65F up to today. Today I added a heater to get it to 70F to see if it waked up some yeast and drops FG a little.

Grain bill:
6.5 lbs 2 Row Malt - Malteurop
1 lbs Coffee Kiln Malt
0.5 lbs Biscuit Malt
1 lbs Cara Vienna
0.5 lbs Chocolate Malt
0.5 lbs Roasted Barley (300)

 

[RPh_Guy]

Did you add pumpkin?

 

[Alex4mula]

Did you add pumpkin?

No. Only the pumpkin spice bag it came with.

 

[RPh_Guy]

Hmm how about lactose? Otherwise why is it called "latte"?

 

[Alex4mula]

Hmm how about lactose? Otherwise why is it called "latte"?

Ops! Yes. It also got 1lb of Lactose at -5min.

 

[RPh_Guy]

Lactose doesn't ferment. -> Higher FG.

 

[Gnomebrewer]

You mean, are they bad or are they just hanging out with the wrong crowd???

Lactose is a dry sugar that gives 46ppg. One pound in 5 gallons is about 9 points. That's 9 points added to OG and FG. So, ignoring the lactose, your 1.020FG beer is at 1.011 which is reasonable for WLP002.

So, in this case, the good guys won!

 

[Vale71]

LOL. I just got an image of a gang of tough looking yeast cells hanging out in a liquor store parking lot...

 

[Alex4mula]

Left is the old yeast. Right is the new one. I think you can see the color difference. The left somehow got to about 78°F on trip home. Never happened before. I think it was maybe warm to begin with. I put it in the fridge as soon as I got home. Next day I bought the right one to be sure. On brew day then both were brought up to 70°F before pitching per instructions.

 

[Vale71]

Color differences can happen with different batches, it's nothing to worry about per se.

But now to seriously answer your question as a sort of apology for my previous facetiousness. No, old yeast will not directly affect the new yeast in any way. What can happen however is that the old yeast could be not completely dead and could to some degree take part in the fermentation and could, as a result of its somewhat compromised state, produce off-flavors and byproducts at higher levels than the healthy yeast, which may or may not end up appreciably affecting the beer's quality.

 

[Alex4mula]

Color differences can happen with different batches, it's nothing to worry about per se.

But now to seriously answer your question as a sort of apology for my previous facetiousness. No, old yeast will not directly affect the new yeast in any way. What can happen however is that the old yeast could be not completely dead and could to some degree take part in the fermentation and could, as a result of its somewhat compromised state, produce off-flavors and byproducts at higher levels than the healthy yeast, which may or may not end up appreciably affecting the beer's quality.

Cool. Thanks!