Stepping starter via dilution instead of decanting?

[MagicMatt]

Hi all,

I was wondering if I could dilute my 2nd step into my 1st step without decanting, and thus save some time from needing to cold crash between the 2 steps.

Typically when I have a 2-step starter it looks like this:

0-24 hrs: Create 1st step (say 0.5L)
24-48 hrs: Cold crash
48-72 hrs: Decant, add 2nd step (say 2.5L)
72-96 hrs: Cold crash

Sometimes I'm running short on time and don't think about it 96 hours in advance. So I was looking for a way to shave some time off, namely the 24 hours cold crashing the 1st step.

The goal of the 2nd step is have it be 'X' volume of ~1.040 wort - but what if I used the volume of fermented liquid (i.e. stale beer) from the 1st step as part of the volume of the 2nd step? Doing this would negate the need to crash the 1st step.

Basically the idea is to add a given concentration/volume of wort such that when mixed with the volume already in the flask, will yield the desired 2nd step volume of 1.040 wort. Obviously the wort from the 1st step will have some residual sugars left depending on the yeast strain, but I was thinking for calculations I can just assume the yeast will attenuate to the median of the range given by manufacturer.

Example:
Step 1: 0.5L of 1.040 wort
Step 2: 2.5L of 1.040 wort

Let's say it's WY1272, which attenuates between 72-76%, and so we'll assume 74%. 74% attenuation of 1.040 wort should yield a finishing gravity of ~1.010. Thus, I'll have 0.5L of 1.010 wort after the 1st step, which is 20% of the total 2nd step volume of 2.5L.

To get to 2.5L of 1.040 wort, I'd need to add 2L of 1.0475 wort:

(20% x 10pts) + (80% x 47.5pts) = 40pts == 2.5L of 1.040 wort


So, my main question is if there is any downside to this? It seems like it would work in theory but I'm not sure how the yeast would respond. Thanks to anyone who can give some input or feedback!

 

[Stand]

I step up starters from frozen stocks, and I dilute using the calculations from BrewUnited: http://www.brewunited.com/yeast_calculator.php

I assumed I didn't need to decant between steps, but that's only an assumption. I've had success stepping up starters by diluting, but that's anecdotal. There are some insanely well-informed yeast-wranglers on these forums that are better suited to answer your question.

I'm interested in hearing from them.

 

[IslandLizard]

Absolutely! Keep doing it as long as your starter vessel can contain the liquid and still function.
That's the method I occasionally use too.

You gain speed in propagation not just due to time lost while cold crashing. The yeast won't go totally "deep" dormant, she's ready to go.

The only downside is you're building up alcohol, but by adding 4x the volume of fresh starter wort, the alcohol % is cut by a factor 5. So drops from 4% to 0.8% by adding the wort, and rather insignificant at that level.

 

[MagicMatt]

Excellent! Yes I had considered the alcohol content but came to the same conclusion as you, that it would be about 4% diluted to <1%. I'd only do this to a maximum of a 3rd step, but likely only 2 steps 99% of the time.

Thanks for the quick replies guys!

 

[Vale71]

Any extract left in the spent wort is unfermentable and should be completely ignored in the calculations since it will provide 0 nourishment for the next step. Just consider the volume of the previous step as if it were dilution water.

The only downside has already been mentioned and it's the residual alcohol that will affect yeast vitality.

 

[IslandLizard]

Any extract left in the spent wort is unfermentable and should be completely ignored in the calculations since it will provide 0 nourishment for the next step. Just consider the volume of the previous step as if it were dilution water.

It's really good to point that out, yes.
Thank you!