2 Vials, 2 Liters, 2 Steps?

[PDevlin75]

Greetings, folks!

Okay, so here's the situation: I'm aiming to brew a 5.5 gal batch of tripel this weekend. So far, I suspect that the OG ought to be about 1.083.

I bought 2 vials of yeast, and added them to a 2 L starter (calc said I'd hit my pitch rate with 2 steps, in a 2L with 2 vials). It started out slow with minimal-to-no foaming after sitting on a stir plate overnight. I had let it keep going while I was at work, and came home to a little bit of spill over. Smelled great, seeing good krausen! All is well!

I was figuring that I'd decant in the fridge tonight, and step it up with another 2 L starter tomorrow night

My questions are:

1) if I'm getting krausen now, should I really decant, or let it keep going until the krausen falls? And....

2) Am I really hitting my pitch rate, or am I possibly growing more yeast in the vial than can feed off of the wort? Is it getting more crowded in there than the food source allows for continued growth?

I figured that it works for stepping up 1 vial in a 1 liter, why not 2 vials in a 2 liter? Or is it just not that simple?

Thanks,
Pete

 

[trentm]

Greetings, folks!

Okay, so here's the situation: I'm aiming to brew a 5.5 gal batch of tripel this weekend. So far, I suspect that the OG ought to be about 1.083.

I bought 2 vials of yeast, and added them to a 2 L starter (calc said I'd hit my pitch rate with 2 steps, in a 2L with 2 vials). It started out slow with minimal-to-no foaming after sitting on a stir plate overnight. I had let it keep going while I was at work, and came home to a little bit of spill over. Smelled great, seeing good krausen! All is well!

I was figuring that I'd decant in the fridge tonight, and step it up with another 2 L starter tomorrow night

My questions are:

1) if I'm getting krausen now, should I really decant, or let it keep going until the krausen falls? And....

2) Am I really hitting my pitch rate, or am I possibly growing more yeast in the vial than can feed off of the wort? Is it getting more crowded in there than the food source allows for continued growth?

I figured that it works for stepping up 1 vial in a 1 liter, why not 2 vials in a 2 liter? Or is it just not that simple?

Thanks,
Pete

1) It has been recommended not to decant until you have cold crashed or in some way allowed the yeast to drop out of suspension. The reason is the cells still in suspension are the least flocculant and therefore probably the most attenuative. In other words, your fermentation needs these guys.

2) While there is some debate on this forum on the effects of inoculation rate of a starter, actually the science is in and there is a tremendous effect. Chris White outlines this well in his book. Assuming the vials had 100% viability (poor assumption) you pitched 100 million cells per ml in your first inoculation and in a non-stirred starter you would expect, according to White, ~150 million cells per ml at finish or 300 billion cells total in your 2l starter. Now if you pitch those 300 billion cells into another 2l starter you will be pitching 150 million cells per ml and this time extrapolating from White (he doesn't give an example at this rate), this may result in ~190 million cells per ml or 380 billion total at completion. As you can see there are fewer new cells created with increased inoculation rates, just as you expected.

Now a couple of things to keep in mind are: 1) These data are from a non-stirred starter experiment. You are using a stirred starter and as with inoculation rates, there is debate on how much advantage you get by stirring a starter (at least on this forum). My experience say this advantage can be significant depending on how vigorous the agitation. 2) The data above are base on 100% viability of the vials. We know this is not realistic.

 

[PDevlin75]

Right on! Thanks for the info!

And to clarify (as I probably should have worded it better the first time), I didn't intend to decant without cold-crashing first... But thank you for the warning, just the same! Yeah, I wasn't sure if I should have waited for the krausen to die down before cold-crashing them. (That would have been the better phrasing).

Well, whatever the cell count, they're in the wort now, and fermenting voraciously! Seriously, I have this thing with a blow-off tube into a one gallon glass carboy in my upstairs hallway closet... I can hear the bubbling from downstairs!

Thanks again!