Stepping up a starter

[Hwk-I-St8]

I'm brewing a big stout this coming weekend with an OG that should be in the 1.113 range (if I can hit 60% brewhouse efficiency). I kicked off a 1.5L starter in my 2L flask Saturday and crashed it last night.

Tonight I need to take the next step but I'm not sure the best way to proceed. As the yeast cell count increases, does the volume of starter wort need to increase? I can't really run bigger than 1.5L and I've had issues with that overflowing before.

The options I've thought of:
1) Create another 1.5L wort, chill and add to the flash after decanting.
2) Decant, save half the slurry and do a starter with the other half and repeat with the saved half.

I've run a couple calculators the the results vary. One asks for the size of the flask so that it won't exceed the size, then calls for a 2nd and third step with 2L of wort in a 2L flask.

Any advice here?

 

[chris000]

yeah, you cannot redo the same size forever. at some point, you will have too many existing cells and they will metabolize the available nutrients too fast.
before I got a bigger flask, I have run the second generation in multiple 2l starters in parallel. if you cannot do that, you could split the "crop" from the 1st starter and only use a portion to seed the following starter while saving the reminder.

 

[mredge73]

I vote for #2.

Your objective is to create more cells; so you need lots of oxygen.
The problem with #1 is that with such a small flask it will be difficult to get every cell to divide after eating; it will be difficult to deliver them enough oxygen.
This is easier with fewer starting cells or if you have access to a bottle of pure O2.

 

[balrog]

I too, vote 2. If you have ANYTHING else like a clean, sanitizable mayo jar, gallon jug, heck even a mixing bowl would work. Split the decanted first starter results and split 1.5L or 2L between them. I also like hitting it with O2.

 

[Hwk-I-St8]

I only have one stir plate and one flask, but I have a ton of other containers and I have time. Here's my proposed process.

Decant and split the initial starter tonight. Store half in one of my 50ml tubes if it will fit. If not, store in a small canning jar (sanitized, of course). Make a new 1.5L starter with the other half. When it's done, cold crash and save the resulting slurry.

Now do the same with the stored half. Combine and pitch the two secondary starter flurries.

I think I should get about 600B cells from this starting worth a fresh packet of yeast.

Spying good?

 

[paneubert]

With only one main flask and one stir plate, I would do one on the plate (like you have been doing) alongside a few others in containers that you shake as often as you can. Like really shake hard and try to get it to really froth up. Decant, save most to fridge, use remainder to make more starters.

Is 600B cells what you need? That should not be hard to grow between now and this weekend. Even if you just used your one flask and plate. Just decant and remove about half the yeast every 24 hours and replace the wort each time you decant. Most of the growth is done within the first 12-18 hours, so letting the starter spin longer than that is not really that helpful. The replication time is something like 90 minutes if I recall correctly. So it doesn't take more than a few hours to have massive exponential growth.

As an example, I just made a 2 step starter starting with a ridiculously small 5mL of slurry that took me about 48 hours and ended up with around 150mL of slurry in a 2 liter vessel. I just put my 5 mL into about 250 mL of wort, then dumped it into about 1.5 liters after 24 hours. 24 after that I had my 150 mL. If you are working with larger starting volumes of yeast, you should be good to go.

 

[homebrewer_99]

When I step up I decant the first beer and add new wort to the remaining yeast.

Since I "can" my wort all I have to do is open up a jar and pour it on the yeast.

I also do this in a gallon jug. A stirplate is also not necessary.