Multiple Yeast Strains During Fermentation

I was wondering the same thing. I have some slurries of US05 and Nottingham that I wanted to pitch on an oatmeal stout I'm about to brew. Was wondering if that is going to create any problems?

 

There is an article in the May/June 2013 issue of Zymurgy entitled "Multiple Personalities: Successfully Blending Yeast Strains," written by Nathan Watkins. If you are a member of the American Homebrewers Association, then I believe you can access the Zymurgy archives for free.

Now, I assume you are mostly curious about combining two different "clean" yeasts. As far as I know, it is unlikely that clean yeasts will interact in complicated ways. (In other words, one might out-compete the other and contribute more flavor, but it is unlikely that together they will create flavors that neither would create on its own.) The same can't be said for clean yeast + brettanomyces, because brett uses phenols produced by the clean yeast to produce some of its own characteristic flavors. This is one reason a mixed fermentation can (somewhat counter-intuitively) produce more "brett" character than a 100% brettanomyces fermentation. You can read a little bit about that here and here.

 

I have two experiences, born out of accidents I won't go into:

Nottingham&Windsor IPA
S-05&WLP530 Belgian Porter

In both cases, I think the flavor characters of the more flavorful yeast (Windsor, WLP530) were diluted by the neutral characters of the other yeasts. The more attenuative strains (Nottingham, S-05) seemed to lead to greater attenuation than my solo experiences with the other yeasts.

There is more to be learned, especially when considering yeast strains that have the capacity to break down maltotriose (e.g., lager strains, Brett) and do other funky things (Brett).

 

Just to add to that, AFAIK all Sacch strains (including Ale strains) can use Maltotriose, but their relative abilities to use it (i.e. how much of it they break down) varies. (This goes for Sacch lager strains too.) The big (theoretical) difference in food sources between Ale Strains and Lager Strains is Raffinose. Lager strains can use it, but Ale strains can't. This is often given as a reason for (many) lager strains having higher attenuation than (many) ale strains, but it's a red herring, because normal beer wort doesn't contain Raffinose.

 

I combine yeast strains a couple times a year. Most recently in a Imperial stout. I used WLP002 and WLP007. Now can I taste the difference with all the roast grains I used? Probably not but was shooting for a little fruity character from the 002 and the attenuation of the 007. I have also used 007 and 530 in a barly wine. This beer would not win any awards because it is out of style however it is my favorite big beer recipe and I will brew it again. I also have brewed lager strains as high as 66 degrees. No need to fear as yeast is a tough animal. Have fun!

 

Adnams use two strains and need both to get the desired attenuation and flavour. The two strains have to be in the right balance, otherwise it won't work properly. I was surprised at how complicated it was.

 

Thanks for that clarification. One thing I was thinking about recently was whether the variability in maltotriose breakdown has more to do with flocculation than enzymatic competence. By extension, lager strains don't flocc so well so they end up slowly chomping on carbs for longer stretches (just speculating; no assertion of fact intended).

 

I think the idea has some merit... i.e. different strains may tend to "give up" and flocculate at different points. Also, FWIW, I believe the enzyme for breaking down Maltotriose is the same enzyme that breaks down Maltose. But the transport mechanism (transport across the cell walls) is different. Which explains why some strains (like champagne strains) are able to eat Maltose (in a half hearted way), but can't eat Maltotriose at all, because it can't get inside the yeast cell.